D.Gould Lippincott's Pocket Neuroanatomy.pdf

LIPPINCOTT’S POCKET

NEUROANATOMY

Douglas J. Gould, PhDProfessor and Vice Chair

Oakland University William Beaumont School of Medicine

Department of Biomedical Sciences

Rochester, Michigan

LIPPINCOTT’S

POCKETNEUROANATOMY

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Library of Congress Cataloging-in-Publication Data

Gould, Douglas J. Lippincott’s pocket neuroanatomy / Douglas J. Gould. p. ; cm. Pocket neuroanatomy Includes index. Summary: “Pocket Neuroanatomy, as a part of Lippincott’s Pocket Series for the anatomical sciences, is designed to serve time-crunched students. The presentation of neuroanatomy in a table format featuring labeled images efficiently streamlines study and exam preparation for this highly visual and content-rich subject. This pocket-size, quick reference book of neuroanatomical pearls is portable, practical, and necessary; even at this small size, nothing is omitted, and a large number of clinically significant facts, mnemonics, and easy-to-learn concepts are used to complement the tables and inform readers”–Provided by publisher. ISBN 978-1-4511-7612-4 I. Title. II. Title: Pocket neuroanatomy. [DNLM: 1. Nervous System–anatomy & histology–Handbooks. WL 39] QM451 611′.8–dc23 2013008263

DISCLAIMER

Care has been taken to confirm the accuracy of the information present and to describe generally accepted practices. However, the authors, editors, and publisher are not responsible for errors or omis-sions or for any consequences from application of the information in this book and make no warranty, expressed or implied, with respect to the currency, completeness, or accuracy of the contents of the publication. Application of this information in a particular situation remains the professional respon-sibility of the practitioner; the clinical treatments described and recommended may not be considered absolute and universal recommendations. The authors, editors, and publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accordance with the current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any change in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new or infrequently employed drug. Some drugs and medical devices presented in this publication have Food and Drug Administration (FDA) clearance for limited use in restricted research settings. It is the responsibility of the health care provider to ascertain the FDA status of each drug or device planned for use in their clinical practice.

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I dedicate this book to my wonderful family—Marie, Maggie, and Lulu—for all of the unconditional love, support, and

patience they offer every day of my life.

vii

Health professions curricula around the world are continually evolving: New discoveries, techniques, applications, and content areas compete for increasingly limited time with basic science top-ics. It is in this context that the foundations established in the basic sciences become increasingly important and relevant for absorbing and applying our ever-expanding knowledge of the human body. As a result of the progressively more crowded curricular landscape, students and instructors are finding new ways to maximize precious contact, preparation, and study time through more efficient, high-yield presentation and study methods.

Pocket Neuroanatomy, as a part of Lippincott’s Pocket Series for the anatomical sciences, is designed to serve time-crunched students. The presentation of neuroanatomy in a table format featuring labeled images efficiently streamlines study and exam preparation for this highly visual and content-rich subject. This pocket-size, quick refer-ence book of neuroanatomical pearls is portable, practical, and neces-sary; even at this small size, nothing is omitted, and a large number of clinically significant facts, mnemonics, and easy-to-learn concepts are used to complement the tables and inform readers.

I am confident that Pocket Neuroanatomy, along with other books in the anatomical science Pocket series, will greatly benefit all students attempting to learn clinically relevant foundational con-cepts in a variety of settings, including all graduate and professional health science programs.

PREFACE

ix

PREFACE

I would like to thank the student and faculty reviewers for their input into this book, which helped create a highly efficient learning and teaching tool. I hope that I have done you justice and created the learning tool that you need.

PREFACEACKNOWLEDGMENTS

xi

Preface viiAcknowledgments ix

CHAPTER 1 Overview of the Nervous System 1

CHAPTER 2 Sensory System 51

CHAPTER 3 Motor System 65

CHAPTER 4 Limbic System 81

CHAPTER 5 Chemical Senses 87

CHAPTER 6 Visual System 91

CHAPTER 7 Auditory and Vestibular Systems 99

CHAPTER 8 Cerebral Cortex 107

Index 111

CONTENTS

1

Overview of the Nervous System 1

ANATOMY

OrientationNeuroanatomical terms of orientation are shared with other vertebrates (e.g., fish). However, because we walk upright, when considering the spinal cord, anterior is more appropriate than ventral and posterior more appropriate than dorsal. Terminology differs at the cephalic flex-ure, at which point the brain changes orientation with regard to the spinal cord so that humans look forward rather than at the sky (FIG. 1-1).

TERMS OF ORIENTATION

Brain Spinal Cord

Anterior/rostral Anterior/ventral

Superior/dorsal Superior/rostral/cranial

Inferior/ventral Inferior/caudal

Posterior/caudal Posterior/dorsal

Anterior(rostral)

Posterior(caudal)

Superior (dorsal)

Dorsal (posterior)

Inferior (ventral) Ventral (anterior)

Rostral

Caudal

Figure 1-1. Orientation terms.

2 LIPPINCOTT’S POCKET NEUROANATOMY

Central Nervous SystemThe central nervous system (CNS) is composed of the brain and spinal cord.

The paired cerebral hemispheres are separated by the longitu-dinal fissure and falx cerebri. They are connected by a large white matter tract, the corpus callosum.

Cerebral HemispheresThe cerebral hemispheres are divided into six lobes (FIGS. 1-2 to 1-4).

DIVISIONS OF THE CENTRAL NERVOUS SYSTEM

Part Division Components

Brain

TelencephalonCerebral hemispheres

Basal nuclei

Diencephalon

Epithalamus

Dorsal thalamus

Hypothalamus

Subthalamus

Brainstem

Midbrain

Pons

Medulla

Cerebellum Anterior, posterior, and flocculonodular lobes

Spinal cord One functional unit

Ascending tracts

Descending tracts

Interneurons

Structure Description Significance

Frontal lobe

Found within the anterior cranial

fossa anterior to the central sulcus

and superior to the lateral fissure

Composed of:

Precentral gyrus

Superior, middle, and inferior

frontal gyri

Gyrus rectus and orbital gyrus

Contains cortex respon-

sible for higher mental

functions (future plan-

ning, personality, judg-

ment, social behavior)

Contains primary, supple-

mentary, and premotor

cortices

Contains Broca’s area for

motor speech

(continued)

CHAPTER 1 OVERVIEW OF THE NERVOUS SYSTEM 3


Parietal lobe

Found posterior to the central sul-

cus, superior to the temporal lobe

and lateral fissure, and anterior to

the occipital lobe

Composed of:

Postcentral gyrus

Superior and inferior parietal

lobules

Precuneus

Contains cortex respon-

sible for visual-auditory-

spatial sensory integra-

tion and orientation

Contains primary and

association sensory

cortex

Temporal lobe

Found within the middle cranial

fossa anterior to the occipital

lobe and inferior to the lateral

fissure

Composed of:

Superior, middle, and inferior

temporal gyri


secondary auditory

cortex

Contains cortex associ-

ated with comprehension

of speech: Wernicke’s

area

Occipital lobe

Found within the posterior cranial

fossa posterior to the parietal

lobe

Composed of:

Cuneate and lingual gyri


secondary visual cortex

Limbic lobe

Found on the medial aspect of the

cerebral hemispheres

Composed of:

Parts of the frontal, parietal, and

temporal lobes

Cingulate and parahippocampal

gyri

Functional area associ-

ated with memory

consolidation and

emotion

Functionally divided

into the:

Hippocampal

formation

Limbic cortex

Amygdala

complex


Superior frontal sulcus

Inferior frontal sulcus

Precentralsulcus

Central sulcus

Frontal lobe

Superior parietallobule

Inferior parietallobule

Wernicke'sarea

Occipitallobe

Superior temporalsulcus

Middle temporalsulcus

Temporal lobe

Lateral fissure

Broca's motorspeech area

Superior frontal gyrus

Orbital gyrus

Parietal lobe

Interparietalsulcus

Frontaleye field

Inferior frontal gyrus

Middle frontal g

yrus

Superior temporal gyrus

Middle temporal gyrus

Inferior temporal

gyrus

Pre

cent

ral g

yrus

Pos

tcen

tral

gyr

us

Supramarginalgyrus

Angular gyrus

Inferior frontal gyrus

Middle frontal g

yrus

Superior temporal gyrus

Middle temporal gyrus

Inferior temporal

gyrus

Pre

cent

ral g

yrus

Pos

tcen

tral

gyr

us

Supramarginalgyrus

Angular gyrus

Figure 1-2. Principal gyri and sulci.

Frontal lobe

Parietal lobe

Superiorfrontal gyrus

Frontalpole

Anteriorcommissure

Hypothalamus

Superior and inferior collilculi

MidbrainPons

Medulla

Spinal cord

CerebellumThalamus

Septum pellucidum

Corpus callosum

Cingulate gyrusPosterior commissure

Parieto-occipitalsulcus

Occipital lobe

Occipital pole

Occipital cortex

Calcarine fissure(sulcus)

Figure 1-3. Midsagittal brain.


ANTERIOR

POSTERIOR

Transverse Section

Extreme capsule1

Interventricularforamen

Anterior horn oflateral ventricle

Lateral fissure

Fornix

Pinealgland

Superiorcolliculus

Insula

Third ventricle

Stria terminalisThalamus

Putamen

Head of caudate nucleus

2

3 Globuspallidus

Lentiformnucleus

Internal capsule 1. Anterior limb 2. Genu 3. Posterior limb

Tail of caudatenucleus

Posterior horn oflateral ventricle

Corpuscallosum

Septumpellucidum

Figure 1-4. Transverse section through diencephalon.


FIBER PATHWAYS ASSOCIATED WITH THE CEREBRUM


Internal

capsule

Funnel-shaped, large

white matter tract

connecting cerebral

cortex with lower

centers

Found between the

thalamus and basal

nuclei

Continuous inferiorly

with the cerebral

peduncles and supe-

riorly with the corona

radiata

Divided into five parts:

1. Anterior limb: Connects anterior

thalamus-cingulate gyrus and dorso-

medial nucleus to prefrontal cortex

2. Posterior limb: Connects motor

cortex to ventral anterior and ventral

lateral nuclei of thalamus

3. Genu: Blend of fibers from anterior

and posterior limbs

4. Sublenticular: Contains auditory

radiations from medial geniculate

nucleus of thalamus to auditory

cortex

5. Retrolenticular: Contains optic

radiations from lateral geniculate

nucleus of thalamus to visual

cortex

Superior

longitudinal

fasciculus

Connects anterior and

posterior aspects of

each hemisphere

Inferior part con-

nects Broca’s and

Wernicke’s areas—

arcuate fasciculus

Lesion of the arcuate fasciculus is associ-

ated with conduction aphasia

Inferior

longitudinal

fasciculus

Connects the occipital

and temporal lobes

Part of the larger occipitotemporal

fasciculus

Corpus

callosum

Large white matter tract

that connects the right

and left cerebral hemi-

spheres

Divided into a rostrum, genu, body, and

splenium

Anterior

commissure

Connects the right and

left temporal lobes

Marks the anterior end of the

diencephalon

Uncinate

fasciculus

Connects the temporal

and frontal lobes

Primarily associated with the limbic

system, connecting the temporal lobe

limbic structures with the orbitofrontal

cortex

Cingulum

Large white matter

pathway that connects

parts of the limbic

cortex

Found within the cingulate and parahip-

pocampal gyri


Additional ConceptsWhite matter fiber pathways that connect cortical areas within a hemisphere are known as association tracts or bundles; those con-necting the hemispheres are commissural.

Basal NucleiSubcortical nuclei of the telencephalon that are associated with the motor system.


Caudate

Together with the

putamen forms the

neostriatum

More medial part of

the corpus striatum

Extensive connections with cerebral

association cortex (i.e., prefrontal

cortex)

Cognitive aspects of movement

Putamen

Together with the

caudate forms the

neostriatum

More lateral part of

the corpus striatum

Forms the outer part of the lentiform

nucleus along with the globus pallidus

The majority of the motor-oriented

cerebral input into the basal nuclei is to

the putamen

Globus

pallidus

Located medial to the

putamen

Divided into external

and internal parts

External part receives input from the

striatum and outputs primarily to the

subthalamic nucleus

Internal part receives afferents from

subthalamic nucleus and striatum and

projects to the thalamus

Subthalamic

nucleus

Part of the dien-

cephalon

Key component of

the indirect pathway

through the system

Receives afferents from the external

segment of the globus pallidus

Projects excitatory efferents to the

internal segment of the globus pallidus

Additional ConceptsBASAL GANGLIA

The basal nuclei are often referred to as the basal ganglia. However, because they are accumulations of neuronal cell bodies found within the CNS, basal nuclei is the more appropriate term.

The term neostriatum is often shortened to striatum in common usage.


FIBER PATHWAYS ASSOCIATED WITH THE BASAL NUCLEI


Ansa lenticularis

Efferent fiber pathway orig-

inating from the internal

segment of globus pallidus

Conveys inhibitory influ-

ence to the ventral lateral

nucleus of the thalamus

Loops around the internal

capsule to join the thalamic

fasciculus

Lenticular

fasciculus

Passes through the internal

capsule to join the thalamic

fasciculus

Thalamic

fasciculus

Fiber pathway containing the

fibers of the combined ansa

lenticularis and lenticular fas-

ciculus, as well as projections

from the cerebellum

Fibers from basal nuclei syn-

apse on ventral lateral nucleus

of the thalamus

Fibers from cerebellum

synapse on ventral anterior

nucleus of the thalamus

Nigrostriatal

pathway

Fiber pathway projecting

from the substantia nigra

pars compacta to the

striatum

Dopamine into the striatum

from the substantia nigra modi-

fies activity through the basal

nuclei

Striatonigral

pathway

Fiber pathway projecting

from the striatum to the sub-

stantia nigra

Efferents from the striatum

to substantia nigra release

γ-aminobutyric acid (GABA) to

decrease output from the sub-

stantia nigra

Additional ConceptsTwo classically described pathways through the basal nuclei are commonly presented (FIG. 1-5), although it should be noted that the interconnections of the nuclei and associated structures are more numerous and complex than is possible to present here.

Disinhibition: When the nucleus responsible for inhibiting the activity of a second inhibitory nucleus, the end result is activity, or in this case, disinhibition.

TERMINOLOGY ASSOCIATED WITH THE BASAL NUCLEI

Term Structures Included

Corpus striatum Caudate, putamen, and globus pallidus

Neostriatum or striatum Caudate and putamen

Pallidum Globus pallidus (both parts)

Lentiform or lenticular nucleus Putamen and globus pallidus


Cortex

Neostriatum

Globus pallidus (M)

Thalamus(VL,VA,CM)

SN

DA

GLU

GLU

GABA

Cortex

Neostriatum

Globus pallidus (L)

GLU

GABA

GABA

Globus pallidus (M)

GABA

GABA

Thalamus(VL,VA,CM)

Direct Pathway

Indirect Pathway

Sth

Figure 1-5. Direct and indirect pathways.


DiencephalonThe diencephalon is located immediately cranial to the brainstem and between the cerebral hemispheres (FIG. 1-6).

Internalcapsule

Insula

Amygdaloid nuclei

Corpus callosum

Lateral ventricle

Caudatenucleus

Internalcapsule

Claustrum

Putamen

Globuspallidus

Optic tract

Hypothalamus

Figure 1-6. Frontal section through diencephalon.


(Dorsal) thalamus

Extends anteriorly to the

anterior commissure,

inferiorly to the hypo-

thalamic sulcus, and

posteriorly to the poste-

rior commissure

Thalami are separated by

the third ventricle

All sensory information, except

olfaction, connects with the

thalamus as it passes to the

cerebral cortex

HypothalamusExtends superiorly to the

hypothalamic sulcus

Coordinates drive-related

behaviors through control of

the autonomic nervous system

and maintains homeostasis

(continued)



EpithalamusPosterior-most part of the

diencephalon

Primary components are the

pineal gland and habenula

SubthalamusPrimary component is the

subthalamic nucleus

Functionally related to the basal

nuclei

Thalamus (Dorsal)The largest part of the diencephalon, the dorsal thalamus—or, more commonly, the thalamus—consists of two large ovoid groups of nuclei, typically interconnected by an interthalamic adhesion (FIG. 1-7). The thalami receive most of the input from the basal nuclei and all sensory input except for olfaction.

Nucleus Input Output

Lateral dorsal Mamillothalamic tract Cingulate gyrus

Lateral posterior Parietal cortex (areas 1 and 5)

Ventral anterior Basal nuclei

Motor cortex (areas 4 and 6)Ventral lateral

Basal nuclei, cerebellum and

red nucleus

Ventral posterior

lateral

Spinothalamic tracts and

medial lemniscus Sensory cortex (areas 3, 1

and 2)Ventral posterior

medial

Trigeminothalamic tracts,

taste (solitary nucleus)

DorsomedialPrefrontal and orbital cortex

and intralaminar nuclei

Prefrontal and orbital cortex,

amygdala, and temporal

cortex

MidlineMotor cortex (area 4) and

globus pallidus

Motor cortex (area 4),

striatum, and diffuse to entire

cortex

Anterior

Hypothalamus via mamillo-

thalamic tract and hippocam-

pus via fornix

Cingulate gyrus

Pulvinar

Association cortex of the

parietal, occipital, and

temporal lobes; medial and

lateral geniculate nuclei; and

superior colliculus

Association cortex of parietal,

occipital, and temporal lobes

Medial geniculateCochlear nerve > Inferior

colliculus

Primary auditory cortex (areas

41 and 42)

Lateral geniculate Retina > Optic tractPrimary visual cortex (area 17)

via the optic radiations

Reticular nucleus All thalamic nuclei


MGN

Thirdventricle

Anterior ANT = anterior nucleus

Reticular TRN = thalamic reticular nucleus

Intralaminar CM = centromedianPF = parafascicular (not shown)

Medial group DM = dorsomedial

Lateral group

LD = lateral dorsalLP = lateral posteriorPUL = pulvinar

Dorsal tier

VA = ventral anteriorVL = ventral lateralVP = ventral posterior(VPL = ventral posterolateral and

Ventral tier

Internal medullary lamina

Cross sectionas indicated

Posterolateral view of left thalamus

ANT

VA

VLVPL

Lateral group

LGN

LP

LD

LD

TRN

DM

PUL

VPM

Internal medullary lamina

CM

DMVL

VPL

Medial group

LGN = lateral geniculate nucleusMGN = medial geniculate nucleus

VPM = ventral posteromedial)

VPM

Figure 1-7. The thalamus.


HypothalamusThe hypothalamus is the inferior-most portion of the diencephalon. It functions with the endocrine system to maintain homeostasis and governs the activities of the autonomic nervous system. It is divided into a series of regions, each of which contain a variety of nuclei (FIG. 1-8). It is also divided into medial and lateral zones.

Region Zone Nuclei Function

AnteriorMedial

Preoptic

Contains sexually dimorphic

nucleus; regulates release of gonad-

otropic hormones; parasympathetic

activity

Supraoptic Secretes oxytocin and vasopressin

Paraventricular

Secretes oxytocin and vasopres-

sin (magnocellular part); secretes

corticotropin-releasing hormone

(parvocellular part)

Anterior

Involved in thermoregulation;

destruction causes hypothermia; role

in sleep regulation

Suprachiasmatic Plays a role in circadian rhythms

Lateral Lateral nuclei Initiates eating and drinking

Opticchiasm

Laminaterminalis

Arcuatenucleus

Ventromedialnucleus

Dorsomedialnucleus

Middle/tuberal area

Pituitarystalk

Posteriornucleus

Posterior area

Mammillarybody

Lateral nucleus

InterthalamicadhesionAnterior

commissure

Fornix(column)

Anterior areaParaventricularnucleus

Anterior nucleus

Supraopticnucleus

Suprachiasmaticnucleus

Thalamus

Optic nerve

Figure 1-8. The hypothalamic nuclei.

(continued)


Additional ConceptsIn general terms, the anterior and medial aspects of the hypothala-mus have a more “parasympathetic” role, and the posterior and lat-eral aspects have a more “sympathetic” function.

There exist functional centers in the hypothalamus:

1. Temperature regulationa. Anterior hypothalamus lesion = Hyperthermiab. Posterior hypothalamus lesion = Hypothermia

2. Food intakea. Ventromedial nucleus lesion = Hyperphagiab. Lateral hypothalamus lesion = Hypophagia

3. Sleep–wake cyclea. Anterior hypothalamus lesion = Insomniab. Posterior hypothalamus lesion = Hypersomnia

4. Emotions: lesion of the ventromedial nucleus = Rage5. Water balance: Lesion of the anterior hypothalamus = Diabetes

insipidus

BrainstemThe brainstem (FIG. 1-9) is the phylogenetically oldest part of the brain. Cranially, it is continuous with the diencephalon, and cau-dally it is continuous with the spinal cord. In addition to providing an important conduit function, it contains circuitry for respiratory and cardiac reflex activity.

Region Zone Nuclei Function

Middle or

Tuberal

Medial

DorsomedialPlays a role in circadian rhythms,

feeding, and emotions

Ventromedial Satiety center

ArcuateSecrete growth hormone–releasing

hormone


PosteriorMedial

Mammillary bodies Memory consolidation

Posterior nucleusHeat conservation center, arousal,

wakefulness




Midbrain

( mesencephalon)

Superior-most part of brainstem

Possesses a tectum composed of

the superior and inferior colliculi

Anterior surface has cerebral

peduncles

Contains the cerebral

aqueduct

Gives rise to the troch-

lear nerve (cranial

nerve [CN] IV)

Pons

Found between the midbrain and

medulla

Located anterior to the cerebel-

lum, to which it is connected by

cerebellar peduncles

Gives rise to the

trigeminal (CN V),

abducent (CN VI),

facial (CN VII), and

vestibulocochlear (CN

VIII) nerves

Medulla

Inferiormost part of brainstem

Continuous inferiorly with spinal

cord at foramen magnum

Anterior surface has pyramids

Gives rise to the glos-

sopharyngeal (CN

IX), vagal (CN X), and

hypoglossal (CN XII)

nerves

Lentiform nucleus

Anteriorcommissure

Mammillary body

Lateralgeniculate body

Vestibulo-cochlearnerve (CN VIII)

Vestibularnerve

Cerebral crus (midbrain)

Cochlearnerve

Olive

Pyramid

Decussation of pyramids

Glossopharyngealnerve (CN IX)

Facial nerve(CN VII)

Trigeminalnerve (CN V)

Oculomotornerve (CN III)

Optic tract

Infundibulum

Optic nerve (CN II)

Optic chiasma

Caudate nucleus

Medulla oblongata

Pons

Anterior View

Figure 1-9. Anterior view of brainstem. (continued)


CerebellumThe cerebellum is involved in the planning, coordination, and mod-ification of motor activities (FIG. 1-10).

Sulcus limitans

PulvinarThalamus

Brachium of inferiorcolliculus

Facial colliculusVestibularnerve

Cochlearnerve

Cuneate tubercleGracile tubercle

Fasciculus gracilis

Fasciculus cuneatus

Hypoglossal trigoneVestibular nucleiCochlear nuclei

SuperiorInferiorMiddle

Inferior colliculusSuperior colliculus

Medialgeniculate body

Lateralgeniculate body

Cerebellarpeduncle

Vestibulo-cochlearnerve(CN VIII)

Third ventricle

Right and left fornix

Posterior View

Cerebral crus

Pineal gland

Figure 1-9. (continued) Posterior view of brainstem.


Anterior- to-posterior

divisions

Anterior

Posterior

Flocculonodular

Anterior is separated from poste-

rior by a primary fissure

Posterior is separated from floc-

culonodular by a posterolateral

fissure

Lateral-to-medial

divisions

Lateral hemisphere

Medial (paravermal)

hemisphere

Vermis

Lateral-to-medial divisions are

based on functional connections

Cerebellar peduncles

Superior

Middle

Inferior

Connect the cerebellum to the

brainstem, mainly the pons


Posterior lobeAnterior lobe

Superior colliculus

Primary fissure

Red nucleus

Substantia nigra


Trigeminal nerve(CN V)

Facial nerve (CN VII)Medulla oblongata

Flocculus

Tonsil

Posterior lobeAnterior lobe

Cerebral crus

Pyramid

Pons

Figure 1-10. Lateral view of cerebellum and brainstem.

Peripheral Nervous SystemThe peripheral nervous system (PNS) is composed of all parts of the nervous system that are not brain or spinal cord, including the cranial and spinal nerves, plexuses, and receptors.

Peripheral ReceptorsNervous system receptors (FIG. 1-11) may be classified by function, axon diameter or conduction velocity or fiber type, morphology or structure, or level of adaptation.

Type of

Mechanoreceptor Structure

Sensory

Modality Fiber Type Adaptation

Free nerve endings

Unencapsulated:

No connective

tissue covering

on end of nerve

fibers

Pain and

temperature

A-δC (unmy-

elinated)

Variable

Merkel’s disc Crude touchA-β or

type IISlow

(continued)


Merkel’s disk

Epidermal-dermalborder

Free nerveending

Meissner’s corpuscle

Hair folliclereceptor

Paciniancorpuscle

Ruffini’s ending

Epidermis

Dermis

Figure 1-11. Peripheral receptors in the skin.

Type of

Mechanoreceptor Structure

Sensory

Modality Fiber Type Adaptation

Pacinian corpuscle

Encapsulated:

End of nerve

fibers enclosed

in connective

tissue, which

assists in recep-

tor function

Pressure and

vibrationVery fast

Meissner’s

corpuscleFine touch

A-β or

type IIFast

Ruffini corpuscleTension and

stretch

Muscle spindleMuscle

stretch

A-α or

type Ia

A-β or

type II

Slow

Golgi tendon organMuscle

tension

A-α or

type Ib


Additional ConceptsTypically, the alphabetical classification system is used for motor fibers, and the numerical is used for sensory fibers. There are many exceptions; for instance, “slow pain” is carried on C fibers, not typi-cally referred to as type IV fibers.

Peripheral NervesA nerve is a collection of axons bound together by connective tissue that serves to transmit electrical signals between the CNS and the periphery (FIG. 1-12).

NERVE FIBERS

Alphabetical

Class

Numerical

Class

Myelinated or

Unmyelinated

Conduction

Velocity

(M/Sec) Innervate

A-αIa

Myelinated

80–120

Annulospiral

endings of muscle

spindles

IbGolgi tendon

organs

A-β II 35–75

Flower-spray

endings from

muscle spindles

A-δ III 5–30

Fibers conducting

crude touch, pain,

and temperature

C IV Unmyelinated 0.5–2

Fibers conducting

pain and tempera-

ture


Cranial

nerve

Olfactory (CN I): Sensory only

Optic (CN II): Sensory only

Oculomotor (CN III): Motor

only

Trochlear (CN IV): Motor only

CN I: Special sense of smell

CN II: Special sense of vision

CN III: Motor to four of six extra-

ocular muscles; parasympathetic

to sphincter pupillae and ciliaris,

and superior tarsal

CN IV: Motor to superior oblique

(continued)



Cranial

nerve

Trigeminal (CN V): Both sen-

sory and motor

Abducens (CN VI): Motor only

Facial (CN VII): Both sensory

and motor

Vestibulocochlear (CN VIII):

Sensory only

Glossopharyngeal (CN IX):

Both sensory and motor

Vagus (CN X): Both sensory

and motor

Spinal accessory (CN XI):

motor only

Hypoglossal (CN XII): Motor

only

CN V: Sensory to face; motor

to eight muscles, including the

muscles of mastication

CN VI: Motor to lateral rectus

CN VII: Motor to muscles of

facial expression; sensory to

external ear; parasympathetic

to submandibular and sub-

lingual salivary glands and

lacrimal gland; special sense

of taste to anterior 2/3 of

tongue

CN VIII: Special sense of hearing

and equilibrium

CN IX: Motor to stylopharyn-

geus; parasympathetic to parotid

gland; sensory to pharynx

and middle ear; special sense

of taste to posterior 1/3 of

tongue

CN X: Motor to palate, larynx,

and pharynx; parasympathetic to

thorax and abdomen; sensory to

external ear

CN XI: Motor to sternocleido-

mastoid and trapezius

CN XII: Motor to tongue mus-

culature

Spinal

nerve

31 pairs

Formed by the merging of

anterior and posterior roots

Terminates as anterior and

posterior primary rami

Divided into:

8 cervical spinal nerve pairs

(C1–C8)

12 thoracic pairs (T1–T12)

5 lumbar pairs (L1–L5)

5 sacral pairs (S1–S5)

1 coccygeal pair

May contain postganglionic

sympathetic, somatic motor, and

sensory fibers


Additional ConceptsCN I is really a loose grouping of fibers from bipolar cells suspended in the upper aspect of the nasal cavity: the fila olfactoria. CN XI originates from the posterior aspect of the anterior horn in the cer-vical spinal cord and is therefore not actually a cranial nerve.

Anterior and posterior roots (rootlets) join to form the spinal nerve. The actual spinal nerve is a very short structure about 1 cm in length, although the term is often used loosely to describe the

Olfactory bulb

Olfactory tract

Optic nerve (CN II)

Optic tract


Trochlearnerve (CN IV)

Motorroot

Trigeminalnerve(CN V)

Abducentnerve (CN VI)

Intermediatenerve (CN VII)

Vestibulocochlearnerve (CN VIII)

Glossopharyngealnerve (CN IX)

Vagusnerve (CN X)

Sensoryroot

Facial nerve (CN VII)

Longitudinal cerebral fissure

Hypoglossalnerve (CN XII)

Cerebellum

Olive

Middlecerebellarpeduncle

Mammillary body

Anteriorperforatedsubstance

Temporal pole

Anterior rootletsof C1 nerve

Optic chiasm

Infundibulum

Pons

Pyramid

Medullaoblongata

Spinal cordInferior View

Spinal accessorynerve (CN XI)

Figure 1-12. Cranial nerves on base of brain.


nerves of the PNS. The spinal nerve terminates by dividing into an anterior and posterior ramus. Somatic plexuses, such as the cervi-cal, brachial, and lumbosacral, are formed only by anterior rami; posterior rami remain segmental.

Each pair of spinal nerves (or spinal cord segment) supplies a strip of skin with sensory innervation: a dermatome. This often differs from the pattern of cutaneous innervation, which is the area of skin supplied with sensory innervation by an individual peripheral nerve. This is a result of peripheral nerves emerging from plexuses, where anterior rami join and exchange fibers from different spinal cord levels. In the trunk, there is no plexus forma-tion, and the pattern of cutaneous innervation and the dermatome are the same.

MNEMONIC

On old Olympus’ towering tops; a fin and German viewed some hops.

This phrase corresponds to the names of cranial nerves.

Olfactory (CN I)Optic (CN II)Oculomotor (CN III)Trochlear (CN IV)Trigeminal (CN V)Abducens (CN VI)Facial (CN VII)Vestibulocochlear (CN VIII), formerly known as the auditory nerveGlossopharyngeal (CN IX)Vagus (CN X)Spinal accessory (CN XI)Hypoglossal (CN XII)

Some say marry money, but my brother says big brains matter more.

This phrase corresponds to the functions of cranial nerves.

Olfactory (CN I): SensoryOptic (CN II): SensoryOculomotor (CN III): MotorTrochlear (CN IV): MotorTrigeminal (CN V): Both sensory and motorAbducens (CN VI): MotorFacial (CN VII): Both sensory and motorVestibulocochlear (CN VIII): Sensory


Glossopharyngeal (CN IX): Both sensory and motorVagus (CN X): Both sensory and motorSpinal Accessory (CN XI): MotorHypoglossal (CN XII): Motor

Spinal CordThe spinal cord extends from the foramen magnum, where it is con-tinuous with the medulla, to a tapering end called the medullary cone, at the L1 to L2 vertebral level (FIG. 1-13). It serves as a reflex center and conduction pathway, connecting the brain to the periph-ery. It gives rise to 31 pairs of spinal nerves.

Feature Description Significance

Cervical

enlargement

Enlarged part of spinal

cord between C4 and T1

Gives rise to anterior rami that

form the brachial plexus; inner-

vates upper limbs

Lumbar

enlargement

Enlarged part of spinal

cord between L1 and S3

Gives rise to anterior rami that

form the lumbosacral plexus; innervates lower limbs

Medullary coneTapered, inferior end of

spinal cord

Located at L1–L2 vertebral level

Nerve roots near conus contrib-

ute to cauda equina

Cauda equina

Collection of anterior and

posterior roots from infe-

rior aspect of spinal cord

Located in the lumbar cistern; a

continuation of the subarachnoid

space in the dural sac caudal to the

medullary cone

Gray matter

Located on the inside of

the spinal cord, deep to

the white matter

Divided into posterior, lateral

(between T1 and L2), and anterior

horns

White matter

Located on the outside of

the spinal cord, external

to the gray matter

Divided into anterior, lateral,

and posterior funiculi; contains

ascending and descending fiber

tracts

DEVELOPMENTThe nervous system begins to form in the third week of develop-ment. The first evidence of the developing nervous system is a thick-ening of the ectoderm of the trilaminar embryo, the neural plate (FIG. 1-14).


Spinal accessorynerve (CN XI) C1 spinal nerve

Arachnoid mater(lining dura mater)

Spinal cord(cervical enlargement)

Posterior rootlets

C8 spinal nerve

Denticulateligament

T5 spinal nerve

Spinal cord(lumbarenlargement)

Conus medullaris

Cauda equina

Termination of dural sac

Filum terminale externum(dural part of filum terminale)

L1spinal nerve

Posteriorramus

Sympathetictrunk

Ramicommunicantes

Intercostal nerve

Spinal ganglion

Posterior View

Foramen magnum

LEFT RIGHT

Figure 1-13. The spinal cord.


Day First

Appears Structure Significance

18 Neural plateThickening of ectoderm between primitive

node and oropharyngeal membrane

20

Neural groove Continued thickening of the neural plate on

its periphery forms a midline neural groove,

with the thickened neural folds along the side

of the grooveNeural fold

22

Neural tube

Neural folds join in the midline to form the

neural tube; fusion of the folds proceeds

cranially and caudally, eventually leaving a

cranial and caudal neuropore

Neural tube separates from surface ecto-

derm to lie between it and the notochord

Cranial part of neural tube forms the brain;

caudal portion forms spinal cord; lumen of

the tube forms central canal of spinal cord

and ventricular system of brain

Cranial neuroporeCloses on ∼day 25; forms lamina terminalis

in adult

Caudal neuropore Closes on ∼day 27

MesodermEctoderm

Neuralplate

Endoderm

Rostral

CaudalNeuralgroove

Neuralfold

Figure 1-14. Dorsum of embryo. (continued)


Clinical SignificanceFailure of the cranial neuropore to close may cause anencephaly, a serious birth defect in which the brain and cranial vault fail to develop. Failure of the caudal neuropore to close may lead to spinal bifida, which includes the following variants (presented in order of severity):

Occulta: Vertebral arch defect onlyCystica, which has two forms:

Meningocele: Meninges project through vertebral arch defect, forming a cerebrospinal fluid (CSF)–filled cystMeningomyelocele: Spinal cord tissue projects through verte-bral arch defect into CSF-filled meningeal cyst

Myeloschisis: Open neural tube

Neural CrestThe neural crest is a migratory population of pluripotent cells that disassociate during formation of the neural tube (FIG. 1-15). Neural crest cells migrate throughout the body to form a multitude of struc-tures in adults.

C D

Neuraltube

Neuralcrest

Somites Neuraltube

Rostral

Caudal

Figure 1-14. (continued)


Structure Significance

Leptomeninges Forms the pia mater and arachnoid

Cells of the autonomic gangliaPostganglionic sympathetic and parasympathetic

cell bodies

Cells of the spinal and cranial

nerve gangliaFirst-order sensory cell bodies

Schwann cells Form myelin in the peripheral nervous system

Chromaffin cellsNeuroendocrine cells found in the adrenal

medulla

Melanocytes Pigment-producing cells of the epidermis

Pharyngeal arch skeletonSkeletal and connective tissue components of the

pharyngeal arches

Aorticopulmonary septumConnective tissue septum that divides the aorta

and pulmonary trunk in the heart

Odontoblasts Cells that form dentin in the teeth

Parafollicular cells Calcitonin-producing cells of the thyroid gland

Neuralplate

Neuralgroove

Neural groove

Neural groove

Neural tube

Neural tube

Neural fold

Neural fold

Notocord

Neural crest

Neural crest

Fusion of newneural fold

Posteriorneuropore

Anteriorneuropore

Figure 1-15. Development of the central nervous system.


Clinical SignificanceBecause neural crest cells migrate so widely throughout the body and are responsible for the appropriate formation of so many struc-tures, disruption of their migration often causes debilitating syn-dromes such as Treacher Collins and Pierre Robin syndrome, which may affect the face, heart, metabolism, and nervous system.

Neural TubeDuring the fourth week of gestation, the neural tube expands and dilates to form vesicles (FIG. 1-16). The lumen of the tube forms the ventricular system of the brain.

Primary Vesicle Secondary Vesicle Adult Structure Ventricular System

Prosencephalon

(forebrain)

Telencephalon

Cerebral hemi-

spheres

Olfactory bulbs

Lateral (two)

ventricles

Diencephalon Thalami Third ventricle

Mesencephalon

(midbrain)Mesencephalon Midbrain Cerebral aqueduct

Neural tube

Brain

Somites

Spinalcord

Neural crest

Melanocytes

Schwann cells

Adrenalmedullary

cells

Spinal ganglion cellsCranial nerve sensory cells

Autonomicganglion

cells

Figure 1-15. Development of the central nervous system.

(continued)


RostralProsencephalon

or forebrain

Mesencephalon

or midbrain

Rhombencephalon

or hindbrain

CaudalA

Figure 1-16. A. Primary brain vesicles. (continued )

Primary Vesicle Secondary Vesicle Adult Structure Ventricular System

Cephalic Flexure

Rhombencephalon

(hindbrain)

MetencephalonPons

Cerebellum Fourth ventricle

Myelencephalon Medulla

Cervical Flexure

Developing Spinal Cord


Telencephalicvesicles

Diencephalon

Optic vesicles

Midbrain

Hindbrain

For

ebra

in

B

TelencephalonProsencephalon(forebrain)

Secondaryvesicles

Adult derivatives

Neural tissue

Cerebralhemispheres

EpithalamusThalamus

HypothalamusNeurohypophysis

Midbrain

Ponscerebellum

Medulla

Cavities

Lateralventricles

Most of3rd

ventricle

Cerebralaqueduct

Rostral4th

ventricle

Caudal4th

ventricle

Primaryvesicles

Mesencephalon(midbrain)

Rhombencephalon(hindbrain)

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon

Spinalcord

Neuraltissue

Cavity

C

Figure 1-16. (continued ) B. Secondary brain vesicles. C. Derivatives of the vesicles.


Additional ConceptsThickenings of the neural ectoderm give rise to (1) olfactory plac-odes, which form CN I and induce formation of the olfactory bulbs, and (2) otic placodes, which form CN VIII and the sensory appa-ratuses of the inner ear.

Clinical SignificanceHydrocephalus is a dilation of the developing ventricles caused by excessive CSF, typically resulting from failure (blockage) of the ventricular drainage system to remove CSF and move it into the circulation.

Neural Tube WallThe neural tube wall is divided into three layers.

Layer Location Significance

Neuroepithelium

(ventricular)

Innermost: Adjacent to

the lumen of tube

Formed of ependymal cells that

line central canal and ventricles

Mantle (interme-

diate)Middle layer

Formed of neurons and glia; gives

rise to gray matter

Marginal OutermostContains nerve fibers from neurons

and glia; gives rise to white matter

Spinal CordThe spinal cord develops from the neural tube, caudal to the fourth pair of somites. It is divided transversely into plates (FIG. 1-17).

Roof platePosterior root

Mantle layer

Ventricular layer

Floor plate

Basal plate

Sulcus limitans

Marginal layer

Alar plate

Figure 1-17. Cross-section through developing spinal cord.


Additional ConceptsThe sulcus limitans is visible in the floor of the fourth ventricle in the adult brainstem and is a useful guide for separating motor and sensory nuclei.

In an infant, the spinal cord extends the length of the vertebral canal; growth of the vertebral canal outpaces that of the spinal cord such that in an adult, the spinal cord only extends to the L1 to L2 vertebral level.

Clinical SignificanceThe dural sac continues to the inferiormost aspect of the vertebral canal. It is filled with the cauda equina, filum terminale, and CSF; thus, because the spinal cord ends at L1 to L2, the dural sac is an excellent place from which to remove CSF as is done in a spinal tap.

NEUROHISTOLOGYThe cells of the nervous system—neurons and glia—are derived from neuroectoderm (FIGS. 1-18 and 1-19).

Plate Position Adult Structures

Alar Posterior/lateral Posterior horns: Sensory

Sulcus Limitans: Separates alar from basal plate

Basal Anterior/lateral Anterior horns: Motor

Roof Posterior Posterior covering of central canal

Floor Anterior Anterior white commissure

Cell Type General Characteristics Identifying Characteristics

Neuron

Generally not capable of

dividing

Capable of sending and

receiving electrochemical

signals

Composed of cell body,

dendrites, and an axon

Multipolar: Most common;

one axon and multiple den-

drites; motor neurons and

interneurons

Bipolar: Sensory only; ganglia

of CN VIII, retina, and olfactory

epithelium


Cell Type General Characteristics Identifying Characteristics

Motor neurons conduct

signals to effector organs;

sensory neurons receive

signals from receptors;

interneurons (internun-

cial) connect motor and

sensory neurons and have

an integrative function

Pseudounipolar: Sensory; sen-

sory ganglia of cranial nerves

and spinal ganglia; mesence-

phalic nucleus

Astrocyte

Most common cell-type

in CNS

Function in/as:

Blood–brain barrier

Ion buffer

Glial scar

Structural support

Glycogen reserve

Metabolic support

Neurotransmitter sink

Synaptic modifier

Fibrous: Found in white matter

Protoplasmic: Found in gray

matter

Radial: Role in guiding neuro-

nal migration during develop-

ment

Microglia

Monocytic origin

Serve as macrophages

migratory

Activated: Phagocytic role

Resting: Inactive form

Oligodendrocyte

Myelin-forming cells of

CNS; one oligodendrocyte

may myelinate parts of

several axons

Satellite cells: Found in gray

matter

Interfascicular: Found in white

matter

EpendymalEpithelial cells that line

central canal and ventricles

Are the epithelial component

of the choroid plexus, which

makes CSF

Schwann

Myelin-forming cells of

PNS; one Schwann cell

myelinates one internode of

one axon

Invest and provide support for

unmyelinated axons


Soma

Pseudounipolar

Bipolar

Multipolar

Figure 1-18. Classification of neurons.


Additional ConceptsMyelin is an electrically insulating wrapping of nerve fibers that forms the myelin sheath. The nerve fibers are wrapped in segments called internodes, with gaps in between called the nodes of Ranvier (FIG. 1-20). The action potential is able to “skip” from node to node in a process called saltatory conduction, thus speeding the signal towards the synapse.

Axon:AxolemmaNeurofibril

Myelinsheath

Node ofRanvier

Myelin sheath

Neurolemma

Fibrousastrocyte

Schwann cell:

CytoplasmNucleus

Oligodendrocytes and Schwann cells

Astrocytes

Ependyma Microglia

Cut axon

Process ofoligodendrocyte

Figure 1-19. Glia.


Additional ConceptsAn individual nerve fiber and myelin sheath (if present) is wrapped in a layer of connective tissue: the endoneurium; the perineurium wraps multiple fibers together in a fascicle. Fascicles and small blood vessels are wrapped in epineurium to form a peripheral nerve.

Clinical SignificanceAxons in the PNS are capable of regeneration if the part of the axon distal to the injury is still intact and the endoneurial sheath is still patent.

MENINGESThe meninges protect and support the brain and spinal cord (FIG. 1-21). From outside to in, the meninges are the dura mater, arachnoid, and pia mater (FIG. 1-22).

PARTS OF A NEURON (FIG. 1-20)

Part Structure Significance

Cell body

(soma)

Large nucleus with Nissl

substance (rough endo-

plasmic reticulum (rER))

Large nucleolus

Lots of mitochondria

Significant rER is evidence of large

protein synthesis role

Cytoskeletal elements composed

of neurofilaments, microfilaments

and microtubules; for vesicle

transport, axonal growth and

structure

Axon

Single

May be myelinated or

unmyelinated

Active transport:

Anterograde (away from

soma), Retrograde (toward

soma)

Dendrite(s)May range from one to

multiple

Conduct impulses towards the

cell body

May possess dendritic spines: Site of synaptic contact


Schwann cellnucleus

Nucleus

Dendrites

Nucleolus

Cell body(soma)

Collateral

Axon Axon

Axon

Neuromuscularjunction

Myelinated fiberUnmyelinated fiber

Muscle fiber

Myelinatedregion

Myelinatedsheath

Unmyelinatedregion

Node ofRanvier

Nissl substance

Axon hillock

Schwann cellnucleus

Figure 1-20. The neuron.

MENINGES AND SPACES AROUND THE BRAIN

Layer (from

outside to in) Description Significance

Skull

Epidural space

Potential space

Contains meningeal

arteries and veins

Site of epidural hematoma; typically

results from trauma to a meningeal

artery

(continued)


Layer (from

outside to in) Description Significance

Dura mater

Tough, inflexible outer

layer

Adherent to inside of

cranial vault

Supplied with blood by

meningeal arteries

Separates into two layers to form

dural septa in several locations

Sensitive to pain (e.g., from

stretching); supratentorial dura is

innervated by CN V; infratentorial

dura is innervated by CN X

Subdural

spacePotential space

Site of subdural hematoma; typi-

cally results from damage to cranial

(bridging) veins

Arachnoid

mater

Delicate layer; adherent

to dura by CSF pressure

and dural border cells

Part of the leptomenin-

ges with the pia mater

Avascular

Lines the dura mater

Evaginations of arachnoid through

the dura enter the superior sagit-

tal sinus via arachnoid villi to

allow CSF to move from subarach-

noid space to venous system

Subarachnoid

space

CSF-filled space

between the arachnoid

and pia

Expanded in several

areas where the arach-

noid bridges over sur-

face irregularities of the

brain to form CSF-filled

subarachnoid cisterns

(i.e., cisterna magna)

Site of subarachnoid hemorrhage;

could be either a cerebral artery

or vein

Spanned by arachnoid trabeculae, which help stabilize the brain

Pia mater


ges with the arachnoid

mater

Adherent to surface of

brain

Highly vascularized membrane

Extends along proximal ends of

blood vessels as perivascular

space

Brain


Spinal arachnoid mater

Spinalpia mater Spinal dura mater

Location offoramen magnum

Cisterna magna

Pia mater

CSF

Subarachnoidspace

Arachnoidvillus

Arachnoidmater

Superior sagittal sinusDuramater

Meningeal layer

Periosteallayer

Figure 1-21. The meninges.

Arachnoidgranulation

CalvariaPeriosteallayer

Meningeallayer

Arachnoid mater

Pia mater

Cerebral artery

Dural septum

Duramater

Coronal Section

Figure 1-22. The meninges (magnified view).


Clinical SignificanceInflammation of the meninges: Meningitis may be viral, bacterial, or caused by some microorganism. It is considered severe owing to its ability to spread quickly around the CNS and because of the proxim-ity of the meninges to the brain and spinal cord.

Dural Folds and SinusesIn several areas in the cranial vault, the dura mater separates into two distinct layers: a periosteal layer that lines the skull and a meningeal layer that forms dural septa that extend into the cranial cavity between parts of the brain for support (FIG. 1-23). In the attached edge of each of the dural septa is a space between the meningeal and periosteal layers of dura: a dural sinus. The dural sinuses are large, ependyma-lined, valveless veins that receive CSF via the arachnoid villi.

Septum Sinus Description

Falx cerebri: Found in the

longitudinal fissure

Superior

sagittal

sinus

Long longitudinally oriented sinus

that receives most arachnoid villi

(and CSF)

Lateral, blood-filled extensions

called lateral lacunae are present

Terminates posteriorly in the con-

fluence of the sinuses

Inferior sag-

ittal sinus

Found in the inferior free edge of

the falx cerebri

Terminates by joining the great

cerebral vein to form the straight

sinus

Tentorium cerebelli: Found

between the occipital lobes

and the cerebellum; divides

cranial vault into supra- and

infratentorial compartments

Straight

sinus

Terminates posteriorly in the conflu-

ence of the sinuses

Transverse

sinus

Tentorial incisure or notch

permits passage of the brainstem

from supra- to infratentorial

regions

Begin at the confluence of the

sinuses

Terminates by changing into the

sigmoid sinus, which is continu-

ous with the internal jugular vein

Falx cerebelli: Found

between the cerebellar hemi-

spheres

Occipital

sinus

Terminates superiorly in the conflu-

ence of the sinuses

(continued)


Septum Sinus Description

Diaphragma sella: Circular

diaphragm over the sel-

lae turcica to protect the

hypophysis; contains aper-

ture for passage of hypophy-

seal stalk

Cavernous

sinus

Pair of sinuses on either side of

the sella turcica, connected by

small intercavernous sinuses

Drain posteriorly into the superior

petrosal sinus (joins the junction

of the transverse and sigmoid

sinuses) and inferior petrosal

sinus (exits the skull via the jugu-

lar foramen to join the internal

jugular vein)

Wall contains: CN III, IV, V1, and V2

Lumen contains internal carotid

artery and CN VI

CSF

Superior sagittal sinus

Arachnoid villus

Skull

Cranialepiduralspace

(potentialspace)

Brain

Arachnoidtrabeculae

Subarachnoidspace

Pia mater

Arachnoidmater

Meningeallayer

Periosteallayer

Cranialdura mater:

Falx cerebri

Figure 1-23. Superior sagittal sinus in frontal section.

Clinical SignificanceLesions affecting the cavernous sinus (e.g., internal carotid artery rupture) may affect the nerves passing through or in the wall. Tumors of the hypophysis (pituitary gland) may compress the sinus, leading to cavernous sinus syndrome, ophthalmoplegia, and sensory loss over the superior aspect of the face.

The cavernous sinus is connected anteriorly with the facial vein through the ophthalmic veins; increased pressure in the facial vein


(e.g., from a bee sting or purulent infection) may be driven into the sinus by the increased pressure.

Meninges and Spaces Around the Spinal CordThe arrangement of the meninges is similar around the spinal cord, but there exist several differences; for example, there are no septae, and there is an epidural space.

Layer (from

Outside to In) Description Significance

Vertebral Canal and Periosteal Covering

Epidural space

Fat-filled space

Location of the internal

vertebral venous plexus

Internal vertebral venous plexus con-

nects superiorly with the occipital

sinus and basilar plexus and provides

a route for the spread of infection to

and from the cranial vault

Dura mater

Tough, inflexible outer

layer

Extends to S2; part infe-

rior to the spinal cord is

the dural sac

Dura mater surrounding the spinal

cord is continuous with the men-

ingeal layer of dura in the cranial

vault

Subdural

spacePotential space Little clinical significance

Arachnoid

mater

Delicate layer; adherent

to dura by CSF pressure

and dural border cells


ges with the pia mater

Avascular

Lines the dura mater: Both extend

to ∼S2 vertebral level, although

spinal cord ends at L1 or L2 level,

creating a large lumbar cistern

Subarachnoid

space

CSF-filled space between

the arachnoid and pia

Expanded

Spanned by arachnoid trabeculae,

which help stabilize the spinal cord

Pia mater


ges with the arachnoid

mater

Adherent to surface of

the spinal cord

Highly vascularized membrane

Extends below the conus medul-

laris as the filum terminale—

internus: inside the lumbar cistern;

externus: outside of the lumbar

cistern connected to the coccyx

21 pairs of lateral extensions; den-

ticulate ligaments stabilize the

spinal cord in the vertebral canal

Spinal Cord


Clinical SignificanceThe lumbar cistern, which contains CSF, nerve roots, and filum ter-minale, is an excellent place to remove CSF for examination (spinal tap) because there is no danger of damaging the spinal cord there (FIG. 1-24).

Anesthetic agents are injected into the spinal epidural space in a paravertebral nerve block, such as is done during childbirth.

VENTRICLES AND CEREBROSPINAL FLUIDThe ventricles form as dilations of the neural tube within the brain and function as ependyma-lined, valveless veins. Each ventricle con-tains choroid plexus consisting of highly convoluted, vascularized epithelium that produces CSF (FIG. 1-25).

A B

AnteriorSpinal cord

Conus medullaris

Posterior

Lumbar cistern

Filum terminaleinternum

Puncture needle(position for adult)

Dura mater

Dural sac

Coccygeal ligament(filum terminale externum)

Vertebral canal

Spinalnerves

Caudaequina

L1

L1

L2

L3

L4

L5

L1

S1

L2

L2

S2

L3L3

S3

L4 L4

S4

L5

L5

S5

Figure 1-24. A. Location of spinal tap. B. The lumbar cistern.


VENTRICLES (PRESENTED IN AN ORDER REPRESENTING THE FLOW OF CSF)

Ventricle Significance

Lateral (2)

Located within the cerebral hemispheres

Five parts

1. Anterior (frontal) horn: Located in frontal lobe

2. Body: In frontal and parietal lobes

3. Inferior (temporal) horn: Located in temporal lobe

4. Posterior (occipital) horn: Located in parietal and occipital lobes

5. Trigone: Junction of body; posterior and inferior horns

Interventricular Foramina (two; of Monro)

Third Thin midline cavity located between the thalami

Cerebral Aqueduct

Fourth Between cerebellum and brainstem

Lateral foramina (two; of Luschka) and Medial foramen (of Magendie)

Subarachnoid Space

Lateral ventricle(body)

Superior sagittal sinus

Interventricularforamen

Anterior horn

Third ventricle

Inferior horn

Cerebralaqueduct

Lateral foramen

Choroid plexus

Choroid plexus

Central canal

Cisterna magna

Medial foramen

Fourthventricle

Posteriorhorn

Subarachnoidspace

Arachnoid villus

Figure 1-25. Flow of cerebrospinal fluid.


Additional ConceptsCSF a clear fluid produced by the choroid plexus at a rate of 500 to 700 mL/day. There is a total of about 150 mL in the CNS at a time. CSF provides support for the CNS, transports hormones, acts as a buffer, and removes wastes. CSF flows through the ventricular sys-tem into the subarachnoid space and into the systemic circulation at the arachnoid villi.

Clinical SignificanceThe trigone of the lateral ventricle contains a large tuft of choroid plexus, the glomus, which calcifies in adults to form a useful land-mark in brain imaging.

Blockage of the interventricular foramina or cerebral aqueduct leads to hydrocephalus, or water on the brain, because CSF drainage is interrupted while production continues.

BLOOD SUPPLYBlood supply to the brain is from two separate pairs of arteries: the vertebrals and the internal carotids.

VESSELS OF THE BRAIN

Artery Origin Description

Internal carotid (2) Common carotid Primary supply to brain

Vertebral (2) Subclavian

Gives rise to basilar, posterior-inferior

cerebellar, and anterior (and posterior)

spinal arteries

Supply meninges, brainstem, and

cerebellum

Anterior cerebral

Internal carotid

Supply medial aspect of cerebral

hemispheres

Middle cerebralSupply lateral aspect of cerebral

hemispheres

Posterior cerebral BasilarSupply inferior aspect of cerebral

hemispheres

Basilar Vertebral

Give rise to anterior inferior cerebellar,

labyrinthine, pontine, superior cerebellar,

and posterior cerebral arteries

Supply brainstem, cerebellum, and

cerebrum

(continued)



Anterior commu-

nicatingAnterior cerebral Forms part of cerebral arterial circle

Posterior

communicating

Joins the poste-

rior and middle

cerebral arteries

Forms part of cerebral arterial circle

Supply cerebral peduncle, internal

capsule, and thalamus

Venous drainage generally follows the arterial pattern and is indirect, draining first

to the dural sinuses and then to veins.

Additional ConceptsThe cerebral arterial circle (of Willis) is located at the base of the brain and is the anastomosis between the vertebrobasilar and inter-nal carotid systems (FIG. 1-26). It is formed by the posterior cerebral, posterior communicating, internal carotid, anterior cerebral, and anterior communicating arteries (FIG. 1-27).

Anterior cerebral arteryAnterior communicating artery

Posteriorcommunicatingartery

Cerebral arterial circle

Superiorcerebellar artery

Pontine arteries

Anterior inferiorcerebeller artery

Posterior inferiorcerebeller

artery (PICA)

Labyrinthine artery

Posteriorspinal artery

Anterior spinal artery

Vertebral artery

Basilar artery

Posteriorcerebral artery

Anterior choroidal artery

Middle cerebral artery

Internal carotid artery

Figure 1-26. Arterial supply of the brain.


Posterior root

Posterior root

Posterior spinalarteries

Posterior inferiorcerebellar artery

Basilar artery

Vertebral artery

Anterior spinal artery

Posterior spinalmedullary artery

Anterior spinalmedullary artery

Posteriorspinal medullary

vein

Anterior spinalmedullary vein

Posterior radicularartery

Anterior radicularartery

Segmented artery

Anterior root

Anterior root

Vertebra

Posterior lateralspinal veins

Anterior lateralspinal veins

Posteriormedian

spinal vein

Anterior medianspinal vein

Posteriorradicular vein

Anteriorradicular vein

Spinalnerve

Figure 1-27. Veins of the spinal cord.


Clinical SignificanceRupture of an artery supplying the brain is a stroke (cerebrovascular accident) and typically manifests as impaired neurologic function. Occlusion may occur by an embolus (clot) blocking arterial flow. Emboli may originate locally or at some distance (the heart).

VESSELS OF THE SPINAL CORD


Vertebral SubclavianGive rise to anterior and

posterior spinal arteries

Anterior spinal VertebralSupplies anterior 2/3 of spinal

cord superiorly

Posterior spinal (2) VertebralSupplies posterior 1/3 of spinal

cord superiorly

Segmental

Ascending cervical, deep

cervical, vertebral, posterior

intercostal, and lumbar

Supply spinal cord and

coverings segmentally

Anastomose with spinal

arteries

Radicular: anterior

and posterior

Segmental

Supply nerve roots and associ-

ated meninges

Variable but prevalent in the

region of the cervical and

lumbosacral enlargements

Supplement spinal arterial

supply

Medullary

Vein Termination Description

Anterior spinal (3) Drained by medullary and

radicular veins

Generally parallel arterial

supply

Eventually drain into the

internal vertebral venous

plexus

Posterior spinal (3)

Medullary Drain into internal vertebral

venous plexusRadicular

Internal vertebral

venous plexus

Drain into dural sinuses of

cranial vault

Communicates with external

venous plexus on external

aspect of vertebrae

Potential route for infection

spread from cranial vault


NEUROTRANSMITTERSNeurotransmitters are molecules that transmit a signal from a neu-ron to an effector (i.e., neuron or muscle cell) across a synapse. The synapse is composed of the presynaptic membrane of the neuron, the synaptic cleft, and the postsynaptic membrane. They may be chemical (use neurotransmitters) or electrical, which consist of gap junctions.

COMMON CENTRAL NERVOUS SYSTEM NEUROTRANSMITTERS

Category Neurotransmitter Effect

Amino acidsGlutamate Excitatory

GABA and glycine Inhibitory

Biogenic amines

DopamineExcitatory (D1 receptors)

Inhibitory (D2 receptors)

Norepinephrine and epinephrine Excitatory

Serotonin Excitatory or inhibitory

Purines Adenosine triphosphate (ATP) Excitatory or modulatory

NeuropeptidesSubstance P Excitatory

Opioids Inhibitory

Acetylcholine Excitatory

Additional ConceptsGlutamate is the most common excitatory neurotransmitter in the CNS; GABA and glycine are the most common inhibitory neu-rotransmitters.

Acetylcholine is used by the autonomic nervous system and at the neuromuscular junction.


Cal

CS

ACAB

FT

H

M

MO

S

STCal

To

SC

BA

FY

FV

C

CS

PIGC

CQ

Cb

D

MO

To

Cb

STBA

R

HCT

GCBV

B

AH CS

SC

Cal

S

PDMD

P

TP

Cb OP

G

W

MCA

TS

A B C

MO

Sagittal Sections

IN

ACA Anterior cerebral arteryAH Anterior horn of lateral ventricleB Body of corpus callosumBA Basilar arteryBV Body of lateral ventricleC ColliculiCal Calcarine sulcusCb CerebellumCQ Cerebral aqueductCS Cingulate sulcusD Dens (odontoid process)F FornixFV Fourth ventricleG Cerebral cortex (gray matter)GC Genus of corpus callosumH HypothalamusHC Head of caudate nucleusI InfundibulumIN Insular cortexM Mammillary bodyMCA Middle cerebral arteryMD MidbrainOP Occipital poleP PonsPD Cerebral pedunclePI Pineal glandR Rostrum of corpus callosumS Splenium of corpus callosumSC Spinal cordST Straight sinusT ThalamusTo Cerebellar tonsilTP Temporal poleTS Transverse sinusW White matterY Hypophysis

Figure 1-28. Sagittal magnetic resonance images through the brain.

IMAGING ATLAS

1Title Title Title Title Title

51

Sensory System 2

BODYThe somatosensory system consists of peripheral receptors, neural pathways, and parts of the brain involved in sensory perception.

Types of Somatosensation Pain and temperature Touch: Fine and crude Vibratory sense Proprioception: Conscious and unconscious (reflex)

Three-Neuron ChainThe somatosensory system uses a three-neuron chain (with some exceptions) to convey information from the periphery to the cere-bral cortex for interpretation and processing.

Neuron Cell Body Location Functions

First orderSpinal ganglia or sensory

ganglia of the head

Conveys sensation from

periphery to the CNS

Second order

Within the central nervous

system (CNS); spinal cord

gray matter or brainstem

Typically gives rise to fibers

that cross the midline to

reach thalamus

Third order Within the thalamus

Conveys sensation from

the thalamus to the cere-

bral cortex

Additional ConceptsThe chain of ascending neurons sends axon collaterals to mediate reflexes and affects other ascending and descending systems, an important concept for pain modulation.

The Anterolateral SystemPain, temperature, and crude touch all ascend the spinal cord as part of the anterolateral system located in the anterior aspect of the lat-eral funiculus and lateral aspect of the anterior funiculus (FIG. 2-1).


Primary sensorycortex

Ventralposterolateral

nucleus ofthalamus

Midbrain

Pons

Rostral medulla

Caudal medulla

Cervicalspinal cord

Thoracicspinal cord

Lumbarspinal cord

Lateralspinothalamic

tract

Spinalganglion

Fibers fromcervical region

Fibers fromlumbar region

Nucleus proprius andSubstantiagelatinosa

Anterior whitecommissure

Posterior horn

Figure 2-1. The anterolateral system.

CHAPTER 2 SENSORY SYSTEM 53

Sense/Tract Description Functions

Pain and

temperature/

lateral spino-

thalamic

Peripheral processes of first-order neu-

rons end as free nerve endings; central

processes enter posterolateral tract

(of Lissauer); synapse on second-order

neurons in posterior horn of spinal

cord, including the substantia gelati-

nosa and nucleus proprius.

Second-order neurons decussate via

the anterior white commissure and

ascend as the lateral spinothalamic

tract; send axon collaterals to brain-

stem reticular formation; terminate

in ventral posterolateral (VPL) nucleus

of thalamus.

Third-order neurons in the VPL of the

thalamus project to the postcentral

gyrus: primary sensory cortex (areas

3, 1, 2) via the posterior limb of internal

capsule.

Mediate pain, tem-

perature, and itch

Somatotopically

organized

Important in the

localization of

stimuli

Reach conscious-

ness

Crude touch/

anterior spino-

thalamic

Peripheral processes of first-order

neurons end as free nerve endings

and on Merkel disks; central processes

synapse on second-order neurons in

posterior horn of spinal cord.

Second-order neurons decussate via

the anterior white commissure and

ascend as the anterior spinothalamic

tract; send axon collaterals to brain-

stem reticular formation; terminate in

VPL of thalamus.



gyrus: primary sensory cortex

(areas 3, 1, 2) via the posterior limb of

internal capsule.

Mediate light touch

Reach conscious-

ness

Pain, tem-

perature

and touch/

spinoreticular

Cell bodies within the CNS are found in

the intermediate gray and anterior and

posterior horns.

Project to multiple synaptic con-

tacts within the brainstem reticular

formation

Much of the tract is composed axon

collaterals from spinothalamic fibers.

Involved in adjusting

the level of attention

to incoming sensation

(continued)


Descending Pain Control MechanismsDescending pain control mechanisms are composed of various descending pathways that serve to inhibit ascending pain infor-mation. The most commonly accepted theory is the gate controltheory of pain. The theory indicates that at each point in the ascend-ing pain pathway, it is possible for a descending fiber to inhibit the ascending pain signal (i.e., act as a “gate” for the transmission). Such points include local inhibition in the spinal cord, brainstem reticular formation, and thalamus.

Additional ConceptsThe primary sensory cortex has a somatotopic organization, which is represented by the homunculus: a representation of the body superimposed on the primary sensory cortex that indicates dispro-portionate representation of some body parts over others (e.g., the hand versus the back) (FIG. 2-2).

Sense/Tract Description Functions

Pain/spinohy-

pothalamic

Cell bodies within the CNS are found in

the intermediate gray and anterior and

posterior horns.

Project to widespread hypothalamic

nuclei

Influence the auto-

nomic response to

incoming pain

Pain, tem-

perature and

touch/spino-

tectal

Fibers that are part of the anterolateral

system terminate in the superior and

inferior colliculi.

Influence reflexive

head movement

Pain/spino-

mesencephalic

Fibers arise from cells in the posterior

horn and ascend as part of the antero-

lateral system.

Influence descending

pain control mecha-

nisms


LegHip

Trunk

Neck

Head

Arm

Elbow

ForearmHand

FingersThumb

EyeNoseFaceUpper lip

LipsLower lip

GumsJaw

Tongue

Pharynx

Intra

-abd

omina

l

Teeth

Toes

Foot

Genitals

A

B

Figure 2-2. A. A somatotopic map of the body surface onto primary somatosensory cortex. B. Somatosensory homunculus.


Tract Description Functions

Anterior spi-

nocerebellar

(FIG. 2-3)

Peripheral processes of first-order neurons end

on Golgi tendon organs and muscle spindles;

central processes enter posterior root to syn-

apse on spinal border cells around the anterior

horn between L1 and S2 cord levels.

Second-order neurons give rise to fibers that

decussate in the anterior white commissure

and ascend in the lateral funiculus as the

anterior spinocerebellar tract; fibers decus-

sate (back to the side of origin) as they enter

the cerebellum via the superior cerebellar

peduncle.

Fibers ascend to cerebellar cortex as mossy

fibers.

Unconscious

propriocep-

tive infor-

mation for

control of

groups of

muscles and

coordination

of the lower

limbs

Act as affer-

ent limb

of stretch

reflexes

Posterior spi-

nocerebellar

(FIG. 2-4A)


on Golgi tendon organs and muscle spindles

primarily in lower limbs; central processes enter

posterior root to synapse on second-order neu-

rons in the posterior thoracic nucleus.

Second-order neurons are located in the pos-

terior thoracic nucleus, only found between

the C8 and L3 cord levels; ascending processes

ascend in the ipsilateral lateral funiculus as the

posterior spinocerebellar tract and enter the

cerebellum via the inferior cerebellar peduncle.

Fibers ascend to cerebellar cortex as mossy

fibers.

Unconscious

propriocep-

tive informa-

tion for fine

coordination

and control

of individual

muscles

Act as affer-

ent limb

of stretch

reflexes

Posterior

spinocerebel-

lar (lower

limb) and

Cuneocere-

bellar (upper

limb) tracts

are homologs

Cuneocere-

bellar

(FIG. 2-4B)


on Golgi tendon organs and muscle spindles,

primarily in upper limbs; central processes

enter fasciculus cuneatus to ascend to synapse

in the medulla on the accessory (lateral) cune-

ate nucleus.

Second-order neurons are located in the acces-

sory cuneate nucleus; give rise to fibers that

enter the ipsilateral cerebellum via the inferior

cerebellar peduncle.

Cerebellar Tracts for the BodyInformation enters the cerebellum from the spinal cord and brain-stem, which the cerebellum uses to coordinate movements. The information includes touch, pressure, and unconscious propriocep-tion from muscle spindles and Golgi tendon organs.


Lowerlimb

Golgitendonorgan

Cerebellum

Superiorcerebellarpeduncle

Pons

Medulla

Anterior (ventral)spinocerebellar

tract

Spinal cord

Figure 2-3. Anterior spinocerebellar tract.

The posterior thoracic nucleus is also known by its eponym, the dorsal nucleus (of Clarke).

Additional ConceptsInterestingly, there is not a well-defined homolog to the anterior spi-nocerebellar tract for the upper limb. This is likely because we do relatively little working of the upper limb musculature in “groups,” such as is done when standing or walking.


A

B

Cerebellum

Posteriorspinocerebellar

tract

Posterior thoracic nucleus

Musclespindle

Lowerlimb

Golgitendonorgan

C8–L2

Cerebellum

Inferior cerebellar peduncle

Musclespindle

Golgitendonorgan

Accessorycuneate nucleus

Cuneocerebellar tract

UpperlimbC7–C1

Fasciculus cuneatus

Inferior cerebellar peduncle(restiform body)

Figure 2-4. A. Posterior spinocerebellar tract. B. Cuneocerebellar tract.


Posterior Columns

Tract Description Functions

Posterior columns

(FIG. 2-5)


neurons innervate Pacinian cor-

puscles, Meissner corpuscles,

Golgi tendon organs, and muscle

spindles; central processes from

the lower limb arrange themselves

somatotopically and ascend as

the fasciculus gracilis, those

from the upper limb form the

fasciculus cuneatus; terminate

on second-order cells in the

nucleus gracilis and cuneatus in

the medulla.

Processes from second-order neu-

rons cross the midline as internal

arcuate fibers at the level of the

sensory decussation in the caudal

medulla; the crossed fibers arrange

themselves somatotopically to

form the medial lemniscus, the

medial lemniscus terminates in the

VPL of the thalamus.

Third-order neurons in the VPL of

the thalamus project to the post-

central gyrus: primary sensory cor-

tex (areas 3, 1, 2) via the posterior

limb of internal capsule.

Convey information

on fine touch, con-

scious propriocep-

tion, and vibratory

sense

Additional ConceptsUnlike other sensory systems, the posterior column pathways do not send axon collaterals to the brainstem reticular formation as they project cranially. The information ascending regarding fine touch does not reflexively initiate a pain control mechanism, nor do they need to “activate” the cortex.

HEADTrigeminal Sensory SystemThe trigeminal sensory system is responsible for all of the various sensory modalities for the face and much of the head, excluding spe-cial senses (FIG. 2-6).


Primary sensorycortex

Ventral posterolateralnucleus of thalamus(third-order neuron) Midbrain

Mediallemniscus

Pons

Fasciculusgracilis

Fasciculus cuneatus

Spinal ganglion(first-order neuron)

C1–C8

T1–T5

L1–L5

S1–S5

Rostralmedulla

Internal arcuate fibers(second-order neurons) Caudal medulla

Fasciculus gracilis

Nucleus gracilis

Nucleus cuneatus

Paciniancorpuscle

Meissner’scorpuscle

Jointcapsules

Merkel’sreceptor

Ruffinicorpuscle

Head

Jaw

Throat

ArmTrunk

Sensory decussation

Hip

LegFoot

T6–T12

Upper body

Lowerbody

Medial lemniscus

Figure 2-5. Posterior column medial lemniscus pathway.


MIDBRAIN

MIDBRAIN

Internal capsuleGlobus pallidus

Posterior trigeminal tract(Trigeminothalamic)

Motorroot

MEDULLA

MEDULLA

Spinal trigeminal nucleus

C2

Substantia gelatinosa

Cerebral cortex(postcentral gyrus)

Sensory area of face,orbit, nose, and mouth

Axon of third-orderneuron in posterior

limb of internal capsule

Ventral posteromedialnucleus

Anterior trigeminal tract(Trigeminothalamic)

Motor nucleus oftrigeminal (V) nerve

Principal sensory nucleusof trigeminal (V) nerve

Spinal trigeminal tract

Spinal trigeminal nucleus

Spinal trigeminal tract

Crossing axons ofsecond-order neuron

Crossing axons ofsecond-order neuron

Axons of second-order neuroncrossing in lower medullaand upper cervical cord

(secondary pain andtemperature fibers)

Dorsolateral fasciculus(tract of Lissauer)

Mesencehphalicnucleus of trigeminal

(V) nerve

PONS

Trigeminal nerve

First-order neuronin CN V ganglion

ThalamusThird ventricle

Figure 2-6. Trigeminal sensory system.


Sense/Structure Description Functions

Pain and tempera-

ture and touch/

spinal trigeminal

tract and nucleus


neurons end as free nerve endings or

contact Merkel disks; first-order cell

bodies are in the trigeminal, genicu-

late, glossopharyngeal, or vagal gan-

glia; central processes enter the brain-

stem via the trigeminal (CN V), facial

(CN VII), glossopharyngeal (CN IX),

or vagus (CN X) nerves; fibers ascend

or descend via the spinal trigeminal

tract to synapse on second-order neu-

rons of the spinal trigeminal nucleus

(C3-midpons) located immediately

medial to the tract.

Second-order fibers cross the midline

to ascend to the VPM of the thalamus

as the anterior trigeminothalamic

tract; fibers also send axon collaterals

to the brainstem reticular formation.



gyrus: primary sensory cortex (areas 3,

1, 2) via the posterior limb of internal

capsule.

The spinal tri-

geminal tract is

a homolog of the

posterolateral

tract

The spinal tri-

geminal tract

allows first-order

central processes

to ascend or

descend: pain,

caudal 1/3; touch,

cranial 2/3

Fine touch, con-

scious propriocep-

tion and vibratory

sense/trigeminal

ganglion


neurons innervate Pacinian and

Meissner corpuscles; first-order cell

bodies are in the trigeminal, genicu-

late, glossopharyngeal, or vagal gan-

glia; central processes terminate on

second-order neurons in the principal

sensory nucleus.

Second-order fibers cross the midline

to ascend as part of the anterior

trigeminothalamic tract to the VPM

of the thalamus; fibers from the

oral region travel bilaterally; those

travelling ipsilaterally form the small

posterior trigeminothalamic tract to

terminate in the ipsilateral thalamus.



gyrus: primary sensory cortex (areas 3,

1, 2) via the posterior limb of internal

capsule.

Functions simi-

larly to the pos-

terior columns of

the spinal cord

The principal

sensory nucleus

is also known as

the chief sensory

nucleus

(continued)


Sense/Structure Description Functions

Unconscious pro-

prioception/mes-

encephalic tract

and nucleus

Peripheral fibers of cells in the mes-

encephalic nucleus innervate muscles

spindles and Golgi tendon organs.

Central processes project to the cer-

ebellum and innervate the trigeminal

motor nucleus to mediate reflexes

and chewing.

Mediates uncon-

scious or reflex

proprioception

from the tem-

poromandibular

joint, periodontal

ligaments, and facial

musculature

Additional ConceptsThe trigeminal ganglion is homologous to a spinal ganglion, con-taining pseudounipolar primary afferents. It is also known as the semilunar or Gasserian ganglion.

CN V, CN VII, IX, and X contribute sensory fibers to the ear, middle ear cavity (CN IX), and external ear (CNs V, IX, and X).

The mesencephalic nucleus is the only population of pseudouni-polar, first-order cell bodies in the CNS. It is important in the jaw-jerk reflex and used by humans primarily as infants for suckling.


65

Motor System 3

PYRAMIDAL SYSTEMThe voluntary motor system is composed of white matter tracts descending from the brain to the periphery. It typically involves a two-neuron chain: an upper motor neuron (UMN) that is located in the central nervous system (CNS) and a lower motor neuron (LMN) that stimulates effectors in the periphery (FIG. 3-1).

Rednucleus

Spinal cord

Reticularnuclei

Anteromedialpathways

Cortex

Lateralpathways

Superior colliculusand vestibular nuclei

Cortico-spinaltract

Motorcortex

Figure 3-1. Descending motor control.


Additional ConceptsThe primary motor cortex has a somatotopic organization, which is represented by the homunculus: a representation of the body super-imposed on the primary motor cortex, which indicates the dispro-portionate representation of some body parts over others (e.g., the hand versus the back) (FIG. 3-2).

PYRAMIDAL SYSTEM: VOLUNTARY PATHWAYS

Tract Description Function

Anterior corticospinal

Axial body

• UMN located in pri-

mary motor cortex,

precentral gyrus:

Brodmann’s area 4;

UMN receives input

from association and

premotor cortex and

motor-related thalamic

nuclei

• UMN fibers descend

via internal capsule

• 90% of corticospinal

fibers decussate in the

pyramidal decussation,

the remaining 10%

cross in the spinal cord

at the level of the LMN

they innervate

• Controls axial musculature

• Most fibers decussate in the

spinal cord (anterior white

commissure)

• Terminate on LMN in medial

intermediate zone at all

levels of the spinal cord

Lateral corticospinal

Distal body

• Controls distal musculature

• Fibers decussate in the caudal

medulla at the pyramidal

decussation

• Terminate on LMN in

anterior horn at all spinal

cord levels

• Axon collaterals that project

to basal nuclei, thalamus,

and reticular formation

are responsible for motor

overlap

• Somatotopically organized

Corticonuclear

( corticobulbar)

Head and face

UMNs descend bilater-

ally, although the major-

ity of the fibers project

to the contralateral LMN

target

• UMNs synapse in the brain-

stem (and cervical cord)

on LMN nuclei associated

with cranial nerves (CNs):

III, IV, V, VI, VII, IX, X, XI,

and XII

• Bilateral control*

*The exception to bilateral control is that innervation of the facial motor nucleus is con-

tralateral only for the lower aspect of the face; the upper parts of the nucleus that control

the upper aspect of the face are innervated bilaterally.

CHAPTER 3 • MOTOR SYSTEM 67

Swallowing

Tongue

Knee

Ankle

Toes

Jaw

Lips

Face

Eyelid andeyeball

Eyebrow

Neck

Thumb

Index

Middle

RingLittle

Hand

Wrist

Elbow

Shoulder

Trunk H

ip

Figure 3-2. Motor homunculus.

EXTRAPYRAMIDAL SYSTEM

EXTRAPYRAMIDAL SYSTEM: INVOLUNTARY PATHWAYS (FIG. 3-3)


Tectospinal

• UMN located in midbrain

tectum; superior and inferior

colliculi

• Fibers descend to contralat-

eral anterior funiculus via

anteromedial aspect of spinal

cord white matter

• Terminate on LMNs in cervi-

cal spinal cord

• Transmits impulses for

reflexive turning of the head

in response to visual and

auditory stimuli

• Fibers cross midline in teg-

mental decussation, result-

ing in primarily contralateral

control


Rednucleus

Basalganglia

Spinal cord

Reticularnuclei

Ventromedialpathways

Cortex

Lateralpathways


Area6

Area4

Motorcortex

Prefrontalcortex

Sensorycortex

Cortico-spinaltract

Thalamus

Figure 3-3. Extrapyramidal motor system.


Reticulospinal:

Pontine and

medullary

• UMN in brainstem reticular

formation; pons and medulla

• Pontine fibers ipsilateral

• Medullary fibers bilateral

• Project to all spinal cord

levels

• Unconscious control of head,

neck, and body

Vestibulospinal:

Medial and

lateral

• UMN in lateral vestibular

nucleus of pons and medial

vestibular nucleus of medulla

• Receive input from mechano-

receptors of inner ear

• Lateral vestibulospinal

pathway is ipsilateral; medial

pathway is bilateral

• Both pathways descend

anteromedial cord

• Lateral vestibulospinals

synapse on LMN at all cord

levels

• Medial vestibulospinals

travel through medial longi-

tudinal fasciculus to synapse

on LMNs in medial aspect of

cervical cord

• Both pathways are involved

in head movement and the

maintenance of posture

EXTRAPYRAMIDAL SYSTEM: INVOLUNTARY PATHWAYS (continued)


Basal Nuclei (Ganglia)A collection of subcortical nuclei involved in stereotyped and volun-tary motor activity, the basal nuclei are the “chief ” control system of the extrapyramidal motor system (FIG. 3-4). There are generally two

Structure Description Function

Striatum

• Caudate + Putamen = Striatum

• Receives input from all regions

of cerebrum and from thalamus

• Output to globus pallidus and

substantial nigra

• Striatum activity inhibits

activity of globus pallidus and

substantia nigra

• Influences pyramidal system

through indirect connections

Globus

pallidus

• Forms medial-most part of len-

tiform nucleus (putamen forms

lateral aspect)

• Divided into external and inter-

nal parts by lamina medullaris

• Receives input from striatum

and subthalamic nucleus

• External part projects to subtha-

lamic nucleus via subthalamic

fasciculus

• Internal part projects to thalamus

via thalamic fasciculus (lenticular

fasciculus and ansa lenticularis)

Primary output from the basal

nuclei

Substantial

nigra*

• Divided into a pars compacta

and pars reticulata; pars com-

pacta composed of cells pig-

mented with melanin

• Both parts have reciprocal con-

nections with striatum via stria-

tonigral and nigrostriatal tracts

• Pars reticulata projects to thalamus

• Loss of dopaminergic

neurons of pars compacta

causes movement disorders;

dopamine regulates activity

through basal nuclei

• Dopamine from the sub-

stantia nigra has an excit-

atory influence on the D1

receptors in the striatum,

which facilitates the direct

pathway, while dopamine

inhibits the D2 receptor, thus

inhibiting activity through

the indirect pathway

Subthalamic

nucleus*

• Part of diencephalon

• Receives inhibitory influence

input from globus pallidus

• Projects excitatory input to the

internal segment of the globus

pallidus

Regulates activity through basal

nuclei

*Groups of cells functionally associated with the basal nuclei.


pathways through the basal ganglia (FIG. 1-5) a movement activator—the direct pathway, and a movement inhibitor—the indirect path-way. The basal nuclei have no direct projection to the spinal cord; rather, they exert their influence indirectly.

Clinical SignificanceLoss of dopaminergic cells in the substantia nigra pars compacta is involved in both Parkinson and Huntington disease.

Damage to the subthalamic nucleus results in ballismus, which is a violent flailing of the limbs. Damage to the striatum leads to bilateral, large-scale, ongoing uncontrolled movements primarily seen in the limbs called choreas.

VL nucleus ofthalamus

Putamen

Striatum

Globuspallidus

SubthalamicnucleusSubstantia

nigra

Caudatenucleus

Figure 3-4. The basal nuclei.


Division Description Function

Sympathetic

• Known as thoracolumbar division

owing to location of pregangli-

onic cell bodies

• Preganglionic neurons use ace-

tylcholine as their neurotrans-

mitter; postganglionics use

norepinephrine

• Preganglionic cell bodies located

in intermediolateral cell column

(T1–L2), project via white rami

communicantes to sympathetic

trunk or paravertebral ganglia

or via thoracic, lumbar, or sacral

splanchnic nerves to prever-

tebral ganglia found within the

aortic plexus

• Responsible for control

of stressed state: fight

or flight

• Results in large energy

expenditure

• Affects large number

of structures: (1) dilator

pupillae: dilates pupil; (2)

salivary glands: increased

viscosity of saliva and

decreased blood flow

to the salivary glands

resulting in less saliva;

(3) heart: accelerates

rate and force; (4) blood

vessels: vasoconstricts;

(5) bronchioles: bron-

chodilates; (6) digestive

tract: inhibits motility;

(7) reproductive system:

ejaculation; and (8) uri-

nary system: activation

Parasympathetic

• Known as craniosacral division

owing to location of pregangli-

onic cell bodies

• Cranial division preganglionic

cell bodies located in brainstem,

associated with CNs:

1. III: Preganglionic nucleus:

accessory oculomotor

(Edinger-Westphal); postgan-

glionic cell bodies located in

ciliary ganglion

• Responsible for control

of the resting state; rest

and repose

AUTONOMIC NERVOUS SYSTEMThe nervous system can be divided into a somatic and an auto-nomic nervous system (ANS); the autonomic or visceral efferent system controls involuntary muscle—smooth and cardiac—and glands throughout the body. Autonomic activity is controlled by the hypothalamus, which is responsible for integrating the ANS and the endocrine system to maintain homeostasis. The ANS is divided into a sympathetic and parasympathetic division (FIG. 3-5). The pregan-glionic cell body is located in the CNS, and the postganglionic cell body is located in a peripheral ganglion for both systems.

(continued)



Parasympathetic

2. VII: Preganglionic nucleus:

superior salivatory;

postganglionic cell bodies

located in pterygopalatine

and submandibular ganglia

3. IX: Preganglionic nucleus:

inferior salivatory; postgan-

glionic cell bodies located in

otic ganglion

4. X: Preganglionic nucleus:

dorsal motor nucleus of

vagus; postganglionic cell

bodies located in wall of

target organ in thorax and

abdomen; supplies parasym-

pathetic innervation up to the

midtransverse colon

• Sacral division preganglionic cell

bodies located in sacral spinal

cord S2–S4, supplies parasym-

pathetic innervation distal to

the midtransverse colon and to

organs of pelvis; preganglionic

fibers travel in pelvic splanchnic

nerves to intramural ganglia in

wall of target organ

• Pre- and postganglionic cell bod-

ies use acetylcholine as their

neurotransmitter

• Responsible for energy

conservation; reduces

heart rate, increases

digestion

• CN III: Constriction of

pupil and accommoda-

tion

• CN VII: Lacrimation,

increased oral and

nasal mucosa secretion,

increased saliva

• CN IX: Increased saliva

• CN X: Increases gastric

motility and secretion,

slows heart rate, and

causes bronchocon-

striction

• Sacral parasympathet-

ics: Lead to erection,

urination, and an

increase in gastric

motility and secretion

Additional ConceptsBecause the parasympathetic system is the energy conservation side of the ANS, it typically exerts more influence over systems than the sympathetic system, although they work in tandem at all times. The postganglionic parasympathetic fibers are very short in the parasympathetic system. In true energy-saving fashion, they are able to activate discreet muscle groups; postganglionic sympathetic fibers are relatively long, leading to massive and often not-situation-appropriate reactions to an emergency.


C1

T1

T10

T11

T12

T4

C8

L1

S1

S2

S4

L2

L5

Brainstem

Spinalcord

Spinalnerves

Sympatheticchain

Hypogastricplexus

Grayramus

Whiteramus

LSN

LSTS

N

LSRSN

GSN

1

2

3

4

5

6

7

Intracranial vessel

Eye

Lacrimal gland

Parotid salivary gland

Sublingual and submandibularsalivary glands

Lungs

Heart

Stomach,small intestine

Liver

Spleen

PancreasAdrenal

Kidney

Distalsmall intestine,large intestine,ascending colon,transverse colon

Transverse colon,distal colon, rectum

Urinary bladder

Male and femalesex organ

Sympatheticfibers

Parasympatheticfibers

Ganglia: Nerves:

PreganglionicPostganglionic

1 = Ciliary2 = Pterygopalatine3 = Otic4 = Submandibular5 = Celiac6 = Superior mesenteric7 = Inferior mesenteric

GSN = Greater splanchnic nerveLSRSN = Lesser splanchnic nerveLSTSN = Least splanchnic nerveLSN = Lumbar splanchnic nerve

Figure 3-5. The autonomic nervous system. (Red, thoracolumbar division; blue, craniosacral division; C, cervical; L, lumbar; S, sacral; T, thoracic.)


Clinical SignificanceDysautonomia is a general term used to describe malfunction of the ANS. It may involve problems with the function of any of the mul-titude of structures innervated by the ANS.

CEREBELLUMThe cerebellum coordinates complex motor movements and is involved in motor learning and skilled planned motor activity. It does not initiate motor activity; rather, it controls or influences the strength, timing, and accuracy of ongoing motor activity.

It is located in infratentorially in the posterior cranial fossa.

Cerebellar PedunclesThe cerebellum is connected to the brainstem by three cerebellar peduncles (FIG. 3-6).

Peduncle Description Function

Superior

• Connects cerebellum to caudal midbrain

and pons

• Contains dentatorubrothalamic, ante-

rior spinocerebellar, and trigeminocer-

ebellar tracts

Major outflow pathway

from cerebellum

Middle • Connects cerebellum to pons

• Contains pontocerebellar fibers

Major input pathway to

cerebellum

Inferior

• Connects cerebellum to rostral medulla

• Two parts: (1) restiform body containing

posterior spinocerebellar tract, cuneo-

cerebellar tract and olivocerebellar

tract and (2) juxtarestiform body con-

taining vestibulocerebellar fibers and

cerebellovestibular fibers

Mixture of cerebellar

afferents and efferents,

mostly input from the

spinal cord

Cerebellar MorphologyThe cerebellum can be divided anterior to posterior and medial to lateral (see Chapter 1).


Rednucleus

Basalnuclei

Spinal cord

Reticularnuclei

Anteromedialpathways

Cortex

Lateralpathways


Thalamus

Area6

Area4

Motorcortex

Prefrontalcortex

Sensorycortex

ThalamusPons,

cerebellum

Cortico-spinaltract

Figure 3-6. Circuitry of the cerebellar cortex.

Cerebellar CortexFrom outside to in, the cerebellar cortex is divided into a molecular layer, Purkinje cell layer, and a granule cell layer (FIG. 3-7).


Climbingfiber

Mossyfiber

Granulecell

Basketcell

Purkinjecell

Purkinje celldendrites

Golgicell

AxonDendrite

Output axon ofdeep cerebellar

nucleus

Parallelfiber

Figure 3-7. The cerebellar cortex.

Layer Description Function

Molecular

• Contains Purkinje

cell dendritic tree

• Contains parallel

fibers of granule cells

• Contains stellate and

basket cells

Site of granule cell excitatory synapse on

Purkinje cell

(continued)


Functional CerebellumFunctionally, the cerebellum can be divided in terms of its involvement in primitive to more advanced movements; such a system includes the deep cerebellar nuclei associated with each division.

Anatomical

Lobe

Phylogenetic

Division

Functional

Division

Deep

Nucleus Function

Anterior PaleocerebellumSpinal cer-

ebellum

Interposed

(globose

+ emboli-

form)

Locomotion:

Walking,

running

Primary Fissure

Posterior NeocerebellumCerebral

cerebellumDentate

Fine movement:

Playing piano,

writing

Posterolateral Fissure

Flocculonodular ArchicerebellumVestibular

cerebellumFastigial

Balance: sitting

upright

Layer Description Function

Purkinje cellContains Purkinje cell

bodies

• Purkinje cells represent the only out-

flow from the cerebellar cortex, always

inhibitory (release γ-aminobutyric acid

[GABA]); project to deep cerebellar

nuclei and vestibular nuclei

• Excited by parallel and climbing fibers

from olivocerebellar tract

• Inhibited by basket and stellate cells

Granule cellContains granule and

Golgi cells

• Granule cells excite (glutamate)

Purkinje, basket, stellate, and Golgi

cells

• Granule cells are inhibited by Golgi

cells

• Granule cells are excited by mossy

fibers (excitatory fibers from spino-

and pontocerebellar tracts)


PHYLOGENETIC DIVISIONS


Vestibulocerebellum

• Also known as archicer-

ebellum

• Pathway begins in inner

ear; travels on CN VIII to

vestibular nuclei in pons,

fastigial nucleus, and floc-

culonodular lobe

• Flocculonodular lobe also

receives input from superior

colliculus (visual informa-

tion) and striate cortex

(visual); projects back out to

vestibular nuclei

• Posture, balance and

equilibrium, and eye

movements

• Allows cerebellum

to coordinate eye

movements with head

movement and posi-

tion to keep images

focused on retina

Spinocerebellum

• Also known as paleocer-

ebellum

• Receives input from spinal

cord and inner ear; also

from mesencephalic nucleus

and cuneocerebellar fibers

(upper limb) to the inter-

posed nuclei (globose and

emboliform)

• Posture, muscle tone,

timing, and accuracy

of ongoing move-

ments, particularly

in the trunk and limb

girdles

• Reciprocal connec-

tions with spinal cord

allows cerebellum to

influence descending

spinal cord control

mechanisms

Neocerebellum

• Also known as pontocer-

ebellum

• Receives both motor and

sensory information from

cerebral cortex

• Information from cortex

relays in pons (pontocer-

ebellar fibers)

• Dentatorubrothalamic tract

projects back out to the red

nucleus and thalamus

• Skilled, learned move-

ments; hand–eye

coordination with

appropriate strength,

timing, and precision

• Cerebellum to red

nucleus allows influ-

ence over all descend-

ing cortical fibers to

influence volitional

movements


Additional ConceptsThe red nucleus projects to the inferior olivary nucleus via the cen-tral tegmental tract, which projects back to the cerebellum, forming a loop or closed circuit. Such cerebellar “circuits,” whereby the cer-ebellar circuit is connected to the descending pathway, allow for the cerebellum to influence the descending pathway based on incoming information from the spinal cord, visual system, and inner ear.

Clinical SignificanceLesions of the flocculonodular lobe or archicerebellar lesions lead to truncal disequilibrium; gait and the trunk are affected. This causes a person to walk on a wide-base, with the trunk swaying when walk-ing. Individuals are unsteady when standing, tend to stagger, and may appear drunk. Possible causes are a cerebellopontine angle tumor or lateral medullary syndrome (i.e., blockage of the posterior inferior cerebellar artery).

Lesions of the anterior lobe or paleocerebellum lesions are often related to alcoholism or malnutrition. The symptoms appear as gross deficits, mainly affecting the trunk and legs. The most promi-nent signs include dystaxia (ataxia)—poor coordination of muscles of gait and stance that cause the legs to be uncoordinated—and dystaxia (ataxia) of the trunk, causing the trunk to bob to-and-fro when walking.

Lesions of the neocerebellum or lateral hemisphere are often unilateral and may combine with anterior lobe and vermal symp-toms. Lesions of the cerebellar hemispheres, dentate nucleus (ante-rior inferior cerebellar artery), or superior cerebellar peduncle (dentatorubrothalamic tract) may also affect speech and eye move-ment. Symptoms are most obvious in the upper extremity in rapid, fine movements.


81

Limbic System 4

THE LIMBIC SYSTEMThe limbic system is a collection of structures deep in the brain that are collectively involved in emotional memory, behavior, and memory consolidation (FIG. 4-1). The structures of the limbic system may be grouped into the medial and basal forebrain, medial tempo-ral lobe, and limbic lobe. The limbic system activities are expressed through the hypothalamus.

Spinal cord

Integrated motor andautonomic response

Sensory Association Motor

Cerebral cortex

Limbic structures

Hypothalamus

PAG

Somatomotorregions

Autonomicregions

Sensoryregions

Reticularformation

Figure 4-1. Information flow to and from the limbic system. (PAG, periaqueductal gray.)


(continued)

Group Parts Description Function

Medial and

basal fore-

brain

Septal area

• Located close to the mid-

line and inferior to the cor-

pus callosum on the medial

aspect of the frontal lobe

• Connections:

1. Hippocampal formation

via the fornix

2. Hypothalamus via the

medial forebrain bundle

3. Habenula via the stria

medullaris

4. Cerebral cortex via dif-

fuse projections

Involved in the

regulation of

appropriate

attention to

stimuli and of

motivation,

stimulation

results in feel-

ings of pleasure

Ventral forebrain

• General region at base of

frontal lobe deep to septal

area cortex and below ante-

rior commissure

• Connections:

1. Cerebral cortex

2. Thalamus

3. Substantia nigra

4. Cingulate gyrus

5. Limbic system

6. Parahippocampal gyrus

Regulates body

posture and

muscle tone

that accompany

behavior and

emotional

states, such as

fear, stress, and

pleasure

Medial tem-

poral lobe:

Hippocampal

formation

and uncus

Hippocampus:

Part of hippo-

campal formation

• Located along medial

aspect of cerebrum; bor-

ders the inferior horn of the

lateral ventricle within the

temporal lobe

• Connections:

1. Septal area via fornix

2. Hypothalamus (including

mammillary bodies) via

fornix

3. Dentate gyrus

4. Subiculum

5. Parahippocampal gyrus

Functions in

learning and

memory, short-

term memory

consolidation

into long-term

memory, and

recognition of

novelty

Dentate gyrus:

Part of hippo-

campal formation

• Located within temporal lobe

• Connections:

1. Hippocampus

2. Entorhinal cortex via fornix

CHAPTER 4 • LIMBIC SYSTEM 83

Group Parts Description Function

Limbic lobe

Cingulate gyrus

• Long, arching gyrus supe-

rior to the corpus callosum

• Connections:

1. Cerebral cortex

2. Thalamus

3. Mammillary bodies

4. Hypothalamus


6. Septal area

7. Amygdala

8. Brainstem

Memory forma-

tion and emo-

tional response

to stimuli; regu-

lation of vis-

ceral responses

that accompany

behavior

Parahippocampal

gyrus

• Parallels and lies deep to

hippocampus

• Continuous posteriorly

with the cingulate gyrus

• Major component is ento-

rhinal cortex

• Connections:

1. Cerebral cortex


Amygdala

• Located within antero-

medial aspect of temporal

lobe, deep to the uncus

• Connections:

1. Temporal and prefrontal

cerebral cortex

2. Thalamus

3. Hypothalamus

4. Septal area

5. Corpus striatum

6. Brainstem

• Regulates

level of

aggression

in behavioral

and emo-

tional states,

stimulation

results in rage

and anxiety

• Receives typi-

cal sensory

input: somato-

sensory, sight,

smell, visceral

sensation,

auditory and

also receives

sensory input

on level of

comfort

or anxiety

(from cortical

sources)


Additional ConceptsThe Papez circuit (FIG. 4-2) is the first pathway described involving the limbic system properly. It includes the cingulate gyrus to the hippo-campal formation to the hypothalamus (mammillary bodies) to the anterior nucleus of the thalamus back to the cingulate gyrus.

Projections from the amygdala and hipppocampus to the striatum influence motor activity as it relates to mood and emotion.

Emotional coloring

Cingulatecortex

Hippocampus

Hypothalamus

Anterior nucleusof thalamus

Fornix

HippocampusHypothalamus

Anterior nucleus ofthalamus

Cingulatecortex

Neocortex

Emotional experience

Emotional expression

Fornix

Neocortex

Figure 4-2. Papez circuit.

CHAPTER 4 • LIMBIC SYSTEM 85

Whereas stimulation of the amygdala causes stress and anxiety, stimulation of the septal area causes pleasure and relaxation; these two systems balance control of emotional responses depending on circumstances.

The limbic system consolidates memory by long-term potentia-tion, the mechanism of memory consolidation (FIG. 4-3). One syn-apse fires in a particular temporal pattern, making it more likely that the synapse will be activated by the same pattern in the future. The more the synapse is activated, the more likely it will be activated in the future, allowing stimuli and responses to be paired.

1 2 3

1 2 3

LTP

Postconditioningmeasurements

Baseline measurements

NMDA receptor

Axon

Den

drite

AMPA receptor

Axon

Den

drite

Ca2+

Ca2+

Ca2+

Before LTP induction

Apply conditioning stimulationto produce strong activationof NMDA receptors

Pos

tsyn

aptic

res

pons

e to

pr

esyn

aptic

sho

ck(%

of b

asel

ine)

PostsynapticEPSP

Presynapticshock

50

100

150

200

During LTP induction After LTP induction

AxonD

endr

ite

–15 0 15 30Time (min)

Figure 4-3. Long-term potentiation.


Clinical ConsiderationsThe hippocampus is one of the first areas to undergo cell death in Alzheimer’s disease; because it is important in consolidation of memories, individuals with Alzheimer’s disease have difficulty in this area. Lesions of the amygdala result in placidity, including loss of fear, rage, and aggression. An animal with a deficit in this area is not likely to last long.

Klüver-Bucy syndrome results from bilateral destruction of the medial aspect of the temporal lobes, including the amygdala and hippocampus, resulting in placidity, hypersexuality, hyperphagia, and visual agnosia.

Korsakoff syndrome, typically a result of thiamine deficiency (often seen in people with alcoholism), leads to cell loss in the hip-pocampal formation and results in amnesia, confabulation, and disorientation.


87

Chemical Senses 5

The chemical senses are those that involve dissolved chemicals in order to initiate impulses from receptors. The chemical senses are olfaction (smell) and gustation (taste).

OLFACTIONOlfaction is a phylogenetically old sense. Various chemicals and chemical concentrations dissolved in the nasal mucosa stimulate an array of olfactory receptors, which are interpreted by the olfactory cortex to create the sense of smell (FIG. 5-1). Our ability to detect the huge range of odors that we are capable of is still poorly understood.

Olfactory bulb

Olfactory tract

Optic chiasm

Amygdala

Entorhinalcortex

Olfactorytubercle

Piriformcortex

Innerplexiform

layerExternalplexiform

layer

Glomerularlayer

Olfactorynerve

To olfactory tract

Granule cellMitral cell

Tufted cell

Glomerulus

From olfactorymucosa

Periglomerularcell

A

B

Figure 5-1. The olfactory system. A. Olfactory cortex. B. Contents of the olfactory bulb. (continued )


Mitralcells

Tufted cells

Olfactory bulb

Medial olfactory tract

Lateral olfactory tract

Contralateralanterior olfactory

nucleus

Basal forebrainlimbic structures

Hippocampus

Prefrontalcortex

Piriformcortex

Amygdala

Entorhinalcortex

C

Olfactory tract

Perforantpathway

Thalamus

Figure 5-1. (continued ) C. Central connections of the olfactory system.

Part Description Connections Function

Olfactory

epithelium

Three cell types:

1. Basal: Stem cells; give

rise to olfactory recep-

tor neurons

2. Supporting: Secrete

granules onto mucosal

surface

3. Receptor: First-order,

bipolar neurons capable

of mitosis; cilia provide

transduction surface

for odor stimulants

Signals are transmit-

ted from the olfac-

tory epithelium to

the olfactory bulb

by passing through

the cribriform plate

of the ethmoid; the fibers passing

through the cribri-

form plate collec-

tively form the olfac-

tory nerve (CN I)

Detects and

responds to

odorants from

the environment

and relays infor-

mation to the

olfactory bulb

Olfactory

bulb

• Site of second-order

neurons: Mitral cells

and tufted cells

• Located on the crib-

riform plate of the

ethmoid

• Receives input from

the olfactory nerve

• Conducts impulse

from olfactory

neurons to olfac-

tory cortex via the

olfactory tract and

lateral olfactory

stria

• Allows a spe-

cific response

to stimulants

through

selective

stimulation of

receptors and

second-order

neurons

Olfactory

tract

Contains anterior olfac-

tory nucleus

Divides into lateral

and medial olfactory

stria

Anterior olfac-

tory nucleus

regulates and

modulates the

distribution of

olfactory infor-

mation

(continued)

CHAPTER 5 • CHEMICAL SENSES 89


Olfactory

cortex

• Site of the third-order

neuron

• Overlies uncus, part of

the prepiriform and

entorhinal cortices

• Possesses a direct corti-

cal projection (bypasses

the thalamus)

Sends impulses to the

dorsomedial nucleus

of thalamus, basal

forebrain, and limbic

system

Allows for spe-

cific perception

of odor through

connections

with limbic sys-

tem: Emotional

response and

memory forma-

tion and retrieval

related to odor

Additional ConceptsThe olfactory receptor cells (neurons) are some of the only neurons in the human nervous system that are capable of mitosis.

Clinical ConsiderationsFracture of the thin cribriform plate that damages the olfactory receptor cells is a common cause of anosmia (loss of smell). Punc-ture or tear of the dura mater is common, causing cerebrospinal fluid to leak from the nasal cavity. Smell returns after regeneration of the receptor cells.

GUSTATION (TASTE)Taste is perceived through stimulation of the taste buds. Flavor is taste plus olfactory, somatosensory, visual, and limbic input. Mood, proximity to the previous meal, temperature, smell, and the appear-ance and feel of food all affect flavor.


Gustatory

receptor

• Located within

taste buds of the

tongue and oral

cavity

• Cilia extend

through taste pore

• Modified epithelial

cells with neuron-

like properties

• Replaced every 1–2

weeks

Depolarized gustatory

cell synapses with first-

order neuron whose

dendrites wrap the cell

• Cilia project

through pore and

are bathed by

saliva; chemicals

cause the cells to

depolarize

• Five tastants:

Sweet, sour, bitter,

salty, and umami

(savory)

(continued)


Clinical SignificanceSmoking is the most common cause of ageusia (loss of taste).


First-order

neuron

• Pseudounipolar

cells located in the

geniculate (CN

VII), petrosal (CN

IX), and nodose

(CN X) ganglia

• Forms afferent limb

of reflex: Coughing,

swallowing

• Carried on pro-

cesses of CNs VII,

IX, and X

• CNs convey impulses

from tongue to

nucleus solitarius

via the solitary tract

• Anterior 2/3 of

tongue: CN VII

• Posterior 1/3 of

tongue: CN IX

• Epiglottis, soft

palate: CN X

Relays neural infor-

mation from tongue

to nucleus solitarius

Second-

order

neuron

Located in medulla

in the gustatory por-

tion (rostral-most) of

nucleus solitarius: the

gustatory nucleus


CNs

• Fibers pass ipsilater-

ally via the central

tegmental tract

to the medial-most

part of the ventral

posteromedial

(VPM) nucleus of the

thalamus

• Projects to parabra-

chial nucleus of pons

• Second-order

neurons of the

nucleus soli-

tarius receive and

combine taste

information from

all three CNs car-

rying taste

• Parabrachial

nucleus passes

taste information

to the hypothala-

mus and amygdala

Third-

order

neuron

Located in the medial-

most part of the VPM

of the thalamus

• Receive input from

nucleus solitarius

• Conveys taste infor-

mation to cortex via

internal capsule

Conveys ipsilateral

taste information

from VPM to gusta-

tory cortex

Gustatory

cortex

• Brodmann’s area 36

• Located near insula

and medial surface

of frontal opercu-

lum near the base

of the central sulcus


VPM

• Projects to orbital

cortex of frontal lobe

and to the amygdala

Integrates taste

information with

other areas (limbic,

olfactory, visual, and

sensory systems) to

produce perception

of flavor


91

Visual System 6

The visual system is responsible for processing images formed from light hitting the retina. It is composed of neural relay systems that begin in the eye, travel in the optic nerve and tract to the lateral geni-culate nucleus (LGN) of the thalamus and finally to the visual cortex.

STRUCTURES


Eye

Composed of three layers

(tunics):

1. Outer: Sclera and

cornea

2. Middle: Choroid, iris, and

ciliary body

3. Inner: Retina

• Retina is com-

posed of seven

layers

• Impulses are

conducted from

superficial to

deep

• Structure of the

eye focuses light

on the retina, par-

ticularly the center

• Impulses from pho-

toreceptors sent to

ganglion cells, which

form the optic nerve

Retina

• Composed of five cell

types, from superficial

to deep:

1. Photoreceptors

2. Bipolar cells

3. Horizontal cells

4. Amacrine cells

5. Ganglion cells

• Optic disk (papilla):

Medial to fovea, blind

spot; contains axons from

ganglion cells

• Macula lutea: Yellow

pigmented area surround-

ing fovea centralis; area

of highest visual acuity;

contains cones only

Photoreceptors are

stimulated, send-

ing an impulse that

eventually stimu-

lates ganglion cells

that form the optic

nerve

Receives focused

images from the cor-

nea and lens, which

initiates an impulse

that is transmitted to

the optic nerve


RetinaThe seven-layered inner tunic of the eye develops as an outgrowth of the diencephalon; it has five cell types within it (FIG. 6-1). The seven layers of the retina from superficial to deep are:

1. Retinal pigmented epithelium2. Photoreceptor layer3. Outer nuclear layer4. Outer plexiform layer5. Inner nuclear layer6. Inner plexiform layer7. Ganglion cell layer

Cell Type Description Connections Function

Photoreceptor

• Two types: Rods and

cones

• Consist of cell body

and synaptic terminal;

respond to light

• Glutamate is the

neurotransmitter

Synapse on bipo-

lar and horizontal

cells

• Rods: Provide

low-acuity

images; mono-

chromatic

• Cones: Provide

images with high

visual acuity;

color vision; need

a lot of light

• Both convert

stimulation from

light into neuro-

nal impulses

Bipolar

• Receive impulse from

photoreceptors

• Located between

inner and outer plexi-

form layer


neurotransmitter

Terminate on

ganglion cells

Provide pathway

from photorecep-

tors to ganglion

cells

Amacrine

• Located between

inner nuclear layer

and outer plexiform

layer

• γ-Aminobutyric acid

(GABA), dopamine,

and acetylcholine act

as neurotransmitters

Synapse on gan-

glion cells in the

outer plexiform

layer

Inhibit ganglion

cells

(continued)

CHAPTER 6 • VISUAL SYSTEM 93

Cell Type Description Connections Function

Horizontal

• Located in the nuclear

and plexiform layers

• GABA is the

neurotransmitter

Synapse on bipo-

lar cells

• Modify the

responses of the

bipolar cells

• Role in color dif-

ferentiation

• Responsible for

lateral inhibition

of photorecep-

tors

Ganglion

• Only source of output

from retina, act as

third-order afferents


neurotransmitter

• Axons leave retina as

optic nerve (CN II)

Axons continue

to optic chiasm as

optic nerve

Influenced by bipo-

lar and horizontal

cells

Additional ConceptsThe ganglion cells form the optic nerve (CN II); they project to the:

• Thalamus (LGN) • Superior colliculus: To mediate visual reflexes and for dynamic

visual map of environment • Hypothalamus (suprachiasmatic nucleus): To mediate circadian

rhythms• Pretectal nucleus: Role in mediating behavioral responses to light:

pupillary light reflex, optokinetic reflex, accommodation reflex, and circadian rhythms. Lateral inhibition is the property of an activated neuron to inhibit excitation of nearby neurons, thereby providing increased discrimination of the excited neuron.

PATHWAYS

Visual PathwayThe visual image is transferred from the retina to the cerebral cortex by the central visual pathway. Along the way, the image is distrib-uted to various parts of the central nervous system (CNS).


CorneaAnteriorchamber

Aqueoushumor

Canal ofSchlemm

Ciliarymuscle(body)

Zonulefibers

Retinalvein

Optic disc

Optic nerveFovea

Macula

Retinalartery

Retina

Choroid

Sclera

Vitreoushumor

Posteriorchamber

Lens

Pupil

Iris

Light

Müllercell

Amacrinecell

Horizontalcell

Externallimitingmembrane

Photoreceptorcells

Ganglioncell

Ganglioncell axons

Bipolarcell

Ganglion cell layer

Inner plexiformlayer

Inner nuclearlayer

Outer plexiformlayer

Outer nuclearlayer

Layer ofphotoreceptorouter segments

Pigmentedepithelium

A

B

Figure 6-1. A. The eye. B. The layers of the retina.


Part Description Connections

Optic nerve

(CN II)

• Actually a myelinated tract of the

diencephalon

• Invested with arachnoid, pia, and

subarachnoid space

• Ganglion cell axons exit

the eye at the optic disk

and travel to the optic

chiasm

• Transmit impulses from

retina to optic chiasm

Optic chiasm

• Impulses from nasal retina cross

midline to join impulses from tem-

poral retina of contralateral eye;

thus, visual information from the

left visual field of both eyes travels

down the right side of the visual

pathway and vice versa

• Located immediately superior to

hypophysis

Receives input from CN II;

nasal retinal fibers cross

and leave posteriorly as

optic tract

Optic tract

Conveys matched visual field infor-

mation from each eye posteriorly; has

fibers from the ipsilateral temporal

hemiretina and contralateral nasal

hemiretina

Connects the optic

chiasm to the LGN of

the thalamus

Lateral genic-

ulate nucleus

• Part of the posterior aspect of the

thalamus

• Composed of six layers, separated

by the visual field to which they are

related:

• Ipsilateral temporal hemiretina

(layers 2, 3, and 5)

• Contralateral nasal hemiretina

(layers 1, 4, and 6)

• And/or identified by cell size:

• Magnocellular layers (layers 1 and

2): Responsible for relaying con-

trast and movement information

• Parvocellular layers (layers 3–6):

Responsible for relaying color and

form information

• Fibers travel to the

occipital lobe as the

geniculocalcarine tract

or optic radiations

• Inferior visual field

fibers terminate on

the superior bank of

the calcarine sulcus,

superior visual field

fibers terminate on the

inferior bank of the cal-

carine sulcus

Optic

radiations

• Fan out as the retrolenticular part of

the internal capsule

• Fibers extending inferomedially

into the temporal lobe are known as

Meyer’s loop

• Transmit impulses from

LGN to primary occipi-

tal cortex

• Left optic radiations

carry all information

from right visual fields of

both eyes and vice versa

(continued)


Part Description Connections

Primary visual

cortex

• Cortical area (17) along the calcarine

sulcus of the occipital lobe

• Visual information is inverted and

reversed upon reaching area 17

• Information from the inferior visual

fields terminates superior to the cal-

carine sulcus on the cuneate gyrus;

information from superior visual

fields terminates inferior to the cal-

carine sulcus on the lingual gyrus

• Primary visual cortex

sorts and sends infor-

mation to other cortical

areas: Visual association

cortices (18 and 19)

• Possesses retinotopic

organization:

• Central part of retina

is represented most

posteriorly and occu-

pies a disproportion-

ately large amount of

the visual cortex

• More peripheral parts

are represented more

anteriorly

Additional ConceptsBecause the optic nerve is a tract of the diencephalon, it is not actu-ally a nerve. A retinotopic organization is maintained from the ret-ina all of the way to the primary visual cortex.

MNEMONIC

The word SLIM can help you remember the relationship between elements of the visual system:

The Superior Colliculus receives input from the Lateral Genicu-late Nucleus. The Inferior Colliculus receives input from the Medial Geniculate Nucleus.

Clinical SignificancePAPILLEDEMA

The optic nerve is part of the diencephalon and as such is invested with arachnoid, pia, and subarachnoid space; increases in intercra-nial pressure compress the nerve, leading to papilledema (swelling of the optic disk).

VISUAL DEFICITS

Visual deficits are named for visual field loss, not retinal loss. The optic chiasm lies immediately superior to the pituitary gland; thus, a pituitary tumor may put pressure on the fibers running through the chiasm. Whereas midsagittal pressure results in bitemporal hemiano-pia, bilateral compression from calcification of the internal carotid arteries in the cavernous sinus may result in binasal hemianopia.


Visual ProcessingVisual processing involves fast and slow conjugate eye movements. Saccades are fast, steplike movements that bring objects onto the retina. The velocity of a saccadic eye movement is too fast for the visual system to relay the information it receives, so the CNS com-putes the size of the movement in advance and initiates it reflex-ively. Smooth, slow tracking movements allow images to stay on the fovea centralis.

Action or Structure Description Function

Saccadic movements

• Fast, steplike move-

ments

• Initiated by the fron-

tal eye fields: part of

the prefrontal cortex

and the superior col-

liculus

• Bring objects of interest onto

retina

• Velocity too great for visual

system, so CNS computes

size of movement in advance

and suppresses perception of

vision during movement

Slow pursuit

movements

Slow, cortically driven

tracking

Allows images to stay on the

fovea centralis

Visual association

cortex

• Brodmann’s areas 18,

19, 20, and 37

• Provides meaning associated

with vision

• Projects “where” information

to parieto-occipital cortex

and projects “what” informa-

tion to occipitotemporal

cortex

• Separates complex visual

information into two

“streams”

1. Dorsal: Where

2. Ventral: What

Additional ConceptsNystagmus is the combined action of a fast saccadic eye movement in one direction and a slow pursuit movement in the opposite direc-tion, which is necessary to keep objects of interest focused on the retina.


99

Auditory and Vestibular Systems 7

The auditory and vestibular systems consist of morphologically and functionally interconnected structures. Both are housed in the inner ear deep in the temporal bone, both send axons centrally that travel in the vestibulocochlear nerve (CN VIII), and disruptions of one system often affect the other.

AUDITORY SYSTEMThe auditory system deals with the sense of hearing. The hearing apparatus is divided into an outer, middle, and inner ear (FIG. 7-1).

Part Description Function

Outer

• Consists of the auricle and

external auditory meatus

• Extends medially to tym-

panic membrane, which

vibrates when sound

vibrations contact it

• Funnels sound from outside world

to tympanic membrane

• Sensory innervation by CNs V, VII,

and X

• Functions in sound localization

Middle

Consists of tympanic mem-

brane, ossicles (malleus, incus,

and stapes), muscles (tensor

tympani and stapedius), and

auditory tube

• Movement of tympanic membrane

causes the ossicles to vibrate in

turn to transmit vibration to oval

window, which leads to inner ear

• Sensory innervation by CN IX

• Muscles dampen sound; auditory

tube equalizes pressure with atmo-

spheric

Inner

• Consists of receptor organs

within the cochlear duct of

the membranous labyrinth

• Vibrations originating at oval

window stimulate hair cells

in cochlear duct; part of the

Organ of Corti

• Vibration of the footplate of the

stapes in the oval window results in

vibration of the basilar membrane,

upon which the Organ of Corti sits;

the Organ of Corti is composed of

receptor cells called hair cells

• Hair cells transduce vibrations into

a neural signal, which is carried cen-

trally by CN VIII


Manubrium

Malleus

IncusPetrous portion

of temporal bone

Stapes

Ovalwindow

Cochlea

Auditorytube

Tympanicmembrane

Externalauditory canal

Pinna

Outer ear Middle ear Inner ear

Sem

icirc

ular

can

als

Posterior

Anterior

Horizontal

AmpullaOval window

Ovalwindow

Round window

Roundwindow

Vestibule Helicotrema

Helicotrema

Scala media

Cochlearnerve

Utricle

Saccule

ScalavestibuliVestibular

membrane

Spiralganglion

Basilarmembrane

Basilarmembrane

Cochlearduct

Haircells

Organ of Corti

Scalatympani

Scalatympani

Scalavestibuli

Stapes

Base

Apex

Tendon ofstapedius

Tensortympani

Vestibularnerve

A

B

C

Figure 7-1. A. The auditory apparatus. B. The inner ear. C. The cochlea.

CHAPTER 7 • AUDITORY AND VESTIBULAR SYSTEMS 101

Additional ConceptsThree features of sounds we perceive:

1. Location: A central nervous system (CNS) comparison mediated by the superior olivary nucleus

2. Frequency: Determined by where along basilar membrane vibra-tion is greatest

3. Amplitude: Determined by the number of hair cells that are stimulated and thereby the number of afferent nerve fibers that are firing

Clinical SignificanceCONDUCTION DEAFNESS

Conduction deafness results when any part of the external or middle ear is damaged in such a way as to impede transfer of sound vibra-tions to the inner ear.

NERVE DEAFNESS

Nerve deafness results from damage to the cochlea, CN VIII, or cen-tral auditory pathway.

Auditory PathwayThe auditory pathway begins with the hair cells of the organ of Corti and ends in the primary auditory cortex (FIG. 7-2).


Organ of Corti

Inner and outer hair cells are

stimulated by movement of

endolymph in the cochlear

duct and movement of the

basilar membrane

Bending of the hair cells causes

depolarization, which stimulates

the first-order afferents of CN VIII

Vestibulocochlear

nerve (CN VIII)

• Contains primary afferent

fibers of auditory system

• Cell bodies located in spi-

ral ganglion located along

the bony modiolus

Transmits impulses from

cochlear duct to cochlear nuclei

of the brainstem

(continued)



Cochlear nuclei

• Located in the medulla

• Receive input from CN VIII

• Divided into a dorsal and

ventral group

• Ventral nuclei project bilaterally

to superior olivary nucleus and

through lateral lemniscus to

contralateral inferior colliculus

• Dorsal nuclei project contra-

laterally to inferior colliculi via

the acoustic stria

• Crossing fibers form the trap-

ezoid body

Superior olivary

nucleus

• Located in the pons

• Conveys information bilat-

erally to inferior colliculi

• Fibers travel in lateral

lemniscus

• Receives input from ventral

cochlear nuclei

• Projects bilaterally

• Involved in sound localiza-

tion by making a temporal

comparison of information

coming from each ear

Inferior colliculi

• Located in midbrain tectum

• Receives input from dorsal

and ventral cochlear nuclei

• Sends impulses to medial

geniculate nucleus of thalamus

• Fibers cross midline via com-

missure of inferior colliculus;

projects to superior colliculus

to mediate audiovisual reflexes

Medial geniculate

nucleusPart of thalamus

• Receives projections from

inferior colliculus

• Projects to auditory cortex via

sublenticular part of internal

capsule, the auditory radiations

Primary auditory

cortex

• Located along supe-

rior temporal gyrus:

Brodmann’s areas 41 and

42, known as the trans-

verse gyrus of Heschl

• Tonotopic organization:

Lower frequencies more

anterior, higher frequen-

cies more posterior

• Input from medial geniculate

nucleus

• Projects to auditory associa-

tion cortex: Area 22

• Responsible for sound

discrimination

Additional ConceptsBecause the cochlear nuclei project bilaterally, to get deafness in one ear, the problem must occur at or proximal to the cochlear nuclei (i.e., organ of Corti, spiral ganglion, or CN VIII).

CN VIII is actually two nerves in one: a cochlear nerve and a vestibular nerve.


Auditorycortex

Medial geniculatenucleus of thalamus

Inferiorcolliculus

Caudal midbrain

Pons–midbrainjunction

Midpons

Nucleus oflateral lemniscus

Laterallemniscus

Superior olivarycomplex

Dorsalacoustic stria

Intermediateacoustic stria

Dorsal cochlearnucleus

Trapezoid body(ventral acoustic stria)

Rostralmedulla

Spiralganglion

(within bonymodiolus)

CN VIII(cochlear nerve)

Ventral cochlearnucleus

Cochlea

Figure 7-2. Central auditory pathway.


Oculomotor nuclearcomplex

Trochlearnucleus

MLFascending

fibers

MLF descendingfibers

Abducensnucleus

Lateralvestibulospinal

tract

SVN

LVNSemicircular

canals: ampullae

Utricle:maculae

Saccule:maculae

Extraocularmuscles

SVN

LVN

MVN

IVN

To extensormotor neurons

To cervicalspinal cord

for adjustmentof head position

To cerebellum

Figure 7-3. Central vestibular pathway. (SVN, superior vestibular nuclei; IVN, inferior vestibular nuclei; MVN, medial geniculate nuclei; LVN, lateral vestibular nuclei.)

VESTIBULAR SYSTEMThe vestibular system is involved with the sense of equilibrium and balance. The semicircular canals are involved in detection of angular or changing movement, whereas the macular organs are involved with perceiving static position (FIG. 7-3).



Semicircular

canals

• Contain receptors for detection

of angular acceleration of the

head

• Cristae ampullari located in

the semicircular canals detect

head movement by endolymph

deformation of hair cells

embedded in the gelatinous

cupula

Deformation of the cilia of the

hair cells stimulates the primary

afferents of CN VIII, the cell bod-

ies of which are located in the

vestibular (Scarpa’s) ganglion

Macular

organs:

Utricle and

saccule

• Contain receptors for linear

acceleration; constant

• Saccule responds maximally

when head is vertical

• Utricle responds maximally when

head is perpendicular to body

• Detects position by maculae;

contains otoliths within gelati-

nous membrane into which cilia

of hair cells are embedded

• Otoliths make the gelatinous

membrane “heavy,” such that

it responds to gravity and does

not allow the gelatinous mem-

brane to reset to resting posi-

tion until head is repositioned

• Deformation of the cilia of

the hair cells stimulates the

primary afferents of CN VIII,

the cell bodies of which are

located in the vestibular

(Scarpa’s) ganglion

Vestibular

ganglion

Contains primary afferent cell

bodies of CN VIII

• Projects centrally to vestibu-

lar nuclei of brainstem

• Projects to cerebellum via

juxtarestiform body

Vestibular

nuclei

• Located in pons and rostral

medulla on floor of fourth

ventricle

• Receive input from CN VIII,

cerebellum, and contralateral

vestibular nuclei

• Outputs to oculomotor, abdu-

cens, and trochlear nuclei via

medial longitudinal fasciculus

• Divided into superior, inferior, medial and lateral nuclear groups

• Fibers to CN III, IV, and VI

nuclei coordinate head and

eye movement and mediate

vestibulo-ocular reflex

• Fibers synapse at cervical

levels of spinal cord via medial

vestibulospinal tract to control

head and neck musculature

• Fibers descend the length of

the spinal cord via the lateral

vestibulospinal tract to control

balance and extensor tone

• Project to cerebellum, con-

tralateral vestibular nuclei,

inferior olivary nuclei, and

thalamus (ventral posterior

inferior and ventral posterior

lateral); project to primary

vestibular cortex (area 2) and

parietal lobe


Additional ConceptsThe vestibulo-ocular reflex (FIG. 7-4) links the vestibular system and eye movement to keep objects of the interest in the center of the retina reflexively during head movement. The eyes move slowly opposite the direction of head movement, thus keeping the object of interest centered on the fovea centralis.

+

+

+

+

–

+

Left eye Right eye

Left abducens(cranial nerve VI)nucleus

Right mediallongitudinalfasciculus

Left oculomotor(cranial nerve III)nucleus

Left vestibularnucleus

Left horizontalsemicircular canal

Rot

atio

n

Lateral rectusmuscle

Lateral rectusmuscle

Medial recti

Direction of eye movements

Turning motion of head

Figure 7-4. The vestibulo-ocular reflex.


107

Cerebral Cortex 8

STRUCTURES AND RELATIONSHIPSThe cerebral cortex is composed of gray matter. It is highly convoluted (folded) into gyri and sulci, which serves to increase the surface area. The cerebral cortex may be classified based on the number of layers it possesses: 6 layered isocortex or neocortex composes most of the human cerebral cortex, while more primitive allocortex has fewer lay-ers. Allocortex is divided into the archicortex of the hippocampus and dentate gyrus, which has only 3 layers and the 3–5 layers paleocortex that serves as the transitional cortex between the neo- and archicortex.

1. Molecular2. External granular3. External pyramidal4. Internal granular5. Internal pyramidal6. Multiform

Neurons in various layers connect vertically to form small function-ally related microcircuits, called columns.

Brodmann’s AreasBrodmann divided the cortex into 47 areas based on cytoarchitec-ture; the areas are still referred to today because they correspond roughly to functional areas (FIG. 8-1).

Regions of the CortexThe cerebral cortex accomplishes complex tasks by having associa-tive areas: areas of the cerebral cortex responsible for related func-tions, integration, and higher processing. Such areas may be classi-fied as unimodal (dealing with a specific function) or multimodal (areas responsible for integrating one or more modalities for higher thought processing). Examples of unimodal areas are the visual, auditory, much of the association cortex (i.e., visual association), premotor cortex, and supplementary cortex. Examples of multi-modal areas are the prefrontal, parietal, and temporal cortices.


Association areas function to produce meaning, quality, and texture to primary areas with which they are associated.

Area Description

Sensory

Primary somatosensory (3, 1, and 2): Postcentral gyrus;

somatotopically organized as sensory homunculus; primarily

involved with localization of sensation

Somatosensory association cortex (5 and 7): Superior parietal

lobule; involved with adding “meaning” to sensation (e.g.,

rough versus smooth, heavy versus light)

Supramarginal gyrus (40): Integrates somatosensory, auditory,

and visual sensation

Primary visual cortex (17): Occipital lobe; vision

Visual association cortex (18, 19, and 39): Angular gyrus;

involved with adding “meaning” to visual stimuli

Primary auditory cortex (41 and 42): Superior temporal gyrus;

hearing

Auditory association cortex (22): Superior temporal gyrus;

language comprehension

Gustatory cortex (43): Parietal operculum and parainsular

cortex; taste

Vestibular cortex (2): Postcentral gyrus; balance and equilib-

rium

Motor

Primary motor cortex (4): Precentral gyrus; initiates voluntary

movement

Premotor cortex (6): Anterior to precentral gyrus on the fron-

tal lobe; prepares primary motor cortex for activity

Supplementary motor cortex (6): Frontal lobe anterior to pre-

central gyrus; contains program for voluntary motor movement

Frontal eye field (8): Middle frontal gyrus; eye movement

Higher function

Prefrontal cortex (9, 10, 11, and 12): Frontal lobe; personality,

motivation, future planning, primitive reflexes

Broca’s speech area (44 and 45): Inferior frontal gyrus; motor

aspect of speech

Wernicke’s speech area (22): Superior temporal gyrus; speech

comprehension

Additional ConceptsHemispheric dominance refers to the side of the brain where lan-guage centers are located. In the majority of people, this is the left hemisphere.

CHAPTER 8 CEREBRAL CORTEX 109

3738

3940

12

3

5

46

7

8

9

10

11

17

18

18

19

19

20

21

22

4142

4445

46

47

A

31

33

34

36

32

12

28

23

24

25

26

27

2930

B

3738

12

3

5

46

7

8

9

10

1117

18

1819

20

19

Figure 8-1. Brodmann’s areas.

AAbducent nerve, 15Accessory cuneate nucleus, 56Accessory oculomotor, 71Acetylcholine, 49, 72Ageusia, 90Alzheimer disease, 86Amacrine cells, 92, 94fAmygdala, 83, 85, 86Anencephaly, 26Anosmia, 89Anterior cranial fossa, 3Anterior funiculus, 51Anterior olfactory nucleus, 88Anterior ramus, spinal nerve, 22Anterior spinocerebellar tract, 56,

57f, 74Anterior trigeminothalamic tract, 62Anterior white commissure, 53Anterograde, 36Anterolateral system, 51–54Aortic plexus, 71Arachnoid trabeculae, 38, 42Arachnoid villi, 38Archicerebellar lesions, 79Arcuate fasciculus, 6Association tracts/bundles, 7Astrocyte, 33, 35fAuditory radiations, 6Auditory system, 99–103

auditory pathway, 101–102, 103fear structure, 99, 100fsounds, features of, 101

Autonomic nervous system (ANS), 71–74, 73f

parasympathetic division, 71–72sympathetic division, 71

Axons, 36

BBallismus, 70Basal cell, 88Basal ganglia. See Basal nucleiBasal nuclei, 7, 69–70, 70f

direct and indirect pathways, 9ffiber pathways associated with, 8terminology associated with, 8

Bipolar cells, 92, 94fBrachial plexus, 22, 23Brain, 2

blood supply to, 45–46, 46f

brainstem, 14–15, 15f–17fcerebellum, 16, 17fcerebral hemispheres, 2–3, 4fdiencephalon, 5f, 10–14, 10fmagnetic resonance images,

51fmeninges and spaces around, 42–43,

39fBrainstem, 14–15

anterior view, 15flateral view, 17fposterior view, 16f

Broca’s area, 3Brodmann’s areas, 107, 109f

CCauda equina, 23, 24fCaudal neuropore, 25, 26Cavernous sinus, 41–42Cells, of nervous system, 32–32, 34f,

35fCentral nervous system (CNS), 2, 65

brain, 2 (see also Brain)development of, 27f–28fneurotransmitters, 49spinal cord, 2, 23, 24f

Central sulcus, 3Central tegmental tract, 90Cephalic flexure, 1Cerebellar tracts, for body, 54, 56–57,

57f, 58fCerebellovestibular fibers, 74Cerebellum, 16, 54, 74–79

circuits, 79cortex, 75–77, 76ffunctional, 77–7lateral view, 17flesions, 79morphology, 74peduncles, 74, 75f

Cerebral aqueduct, 15, 45Cerebral arterial circle, 46, 46f

INDEX

111

Note: Page numbers followed by an f indicate a figure.

112 INDEX

Cerebral cortex, 107–108, 109fBrodmann’s areas, 107, 109fregions of cortex, 107–108

multimodal areas, 107unimodal areas, 107

Cerebral hemispheres, 2, 4ffrontal lobe, 2limbic lobe, 3occipital lobe, 3parietal lobe, 3temporal lobe, 3

Cerebral peduncles, 6, 15, 16fCerebrospinal fluid (CSF), 43, 44f, 45Cerebrum, fiber pathways associated

with, 6Cervical plexus, 22Chemical senses, 87

gustation, 89–90olfaction, 87–89

Chief sensory nucleus, 62Choroid plexus, 33Ciliary ganglion, 71Cingulate gyrus, 83Cisterna magna, 38Climbing fibers, 77Cochlear nuclei, 16f, 102Commissural, 7Conduction aphasia, 6Conduction deafness, 101Cones, 92Confluence of sinuses, 40Conus medullaris, 24fCorona radiata, 6Corpus callosum, 2, 82Corpus striatum, 8Cranial nerves, 19–20, 21f

mnemonics for, 22–23Cranial neuropore, 25, 26Cribriform plate, 88Cuneocerebellar tract, 58f, 74Cutaneous innervation, pattern of, 22

DDendritic spines, 36Dentate gyrus, 82Dentatorubrothalamic tract, 74Denticulate ligaments, 42Dermatome, 22Descending motor control, 65fDescending pain control mechanisms,

54Development, nervous system, 23, 25,

25f–26fDiencephalon, 10–11

frontal section, 10ftransverse section, 5f

Disinhibition, 8Dorsal motor nucleus of vagus, 72Dorsal nucleus (of Clarke), 57Dural border cells, 38, 42Dural sac, 23, 32Dural septa, 38, 40Dural sac, 42Dural sinus, 40Dysautonomia, 74

EEmbolus, 48Endoneurium, 36Entorhinal cortex, 83, 89Ependymal cells, 31, 33, 35fEpidural space

brain, 37spinal cord, 42

Epineurium, 36Ethmoid, 88Extrapyramidal system, 67–70, 68fEye, 91, 94f. See also Retina

FFacial nerve, 15Falx cerebri, 2Fascicles, 36Fasciculus cuneatus, 59, 60fFasciculus gracilis, 59, 60fFlocculonodular lobe lesions, 79Foramen magnum, 15Fovea centralis, 91Free nerve ending, 17, 18fFrontal eye fields, 97

GGanglion cells, 93, 94fGate control theory, of pain, 54Geniculate ganglia, 90Glia, 32, 35fGlomus, 45Glossopharyngeal nerve, 15Glutamate, 49Golgi tendon organs, 56Great cerebral vein, 40Gustation, 89–90Gustatory nucleus, 90Gyri and sulci, 4f

HHabenula, 11Hair follicle receptor, 18f

INDEX 113

Hemispheric dominance, 108Hippocampus, 86Homunculus, 54, 55f, 66, 67fHorizontal cells, 93, 94fHuntington disease, 70Hydrocephalus, 31Hypoglossal nerve, 15Hypoglossal trigone, 16fHypothalamic sulcus, 10Hypothalamus, 10, 13–14

functional centers in, 14functions of, 13hypothalamic nuclei, 13fregions/zones, 13–14

IIndirect pathway, 7, 9fInferior cerebellar peduncle, 56Inferior colliculus, 15, 16f, 54, 67, 102,

103fInferior petrosal sinus, 41Inferior salivatory, 72Intermediolateral cell column, 71Internal arcuate fibers, 59, 60fInternal capsule, 8, 53, 66Internal jugular vein, 40Internal vertebral venous plexus, 42Interventricular foramina, 45

JJuxtarestiform body, 74

KKlüver-Bucy syndrome, 86Korsakoff syndrome, 86

LLamina terminalis, 25Lateral fissure, 3Lateral funiculus, 51Lateral geniculate nucleus, 95Lateral lacunae, 40Lateral olfactory stria, 88Lateral spinothalamic tract, 52fLentiform nucleus, 7, 8Leptomeninges, 38, 42Limbic system, 81–86

information flow to and from, 81fLongitudinal fissure, 2Long-term potentiation, 85, 85fLower motor neuron (LMN), 65Lumbar cistern, 23, 42, 43, 43fLumbar nerve, 71Lumbosacral plexus, 22, 23

MMacula lutea, 91Macular organs, 105Medial geniculate nucleus, 102Medial intermediate zone, 66Medial lemniscus, 59, 60fMedial olfactory stria, 88Medulla oblongata, 15fMedullary cone, 23Meissner’s corpuscle, 18, 18f, 59, 60fMeningeal layer, 40Meninges, brain, 37, 39f

arachnoid mater, 38dura mater, 38inflammation of, 40pia mater, 38

Meningitis, 40Merkel’s disc, 17, 18fMesencephalic nucleus, 61f, 63Meyer’s loop, 95Microglia, 33, 35fMidbrain, 15, 15fMiddle cranial fossa, 4Midsagittal brain, 4fMitral cells, 88Mnemonics

cranial nerveson old olympus’ towering tops; a

fin and german viewed some hops, 22

some say marry money, but my brother says big brains matter more, 22–23

visual systemSLIM, 96

Modiolus, 101Mossy fibers, 56, 77Motor homunculus, 67fMotor system

autonomic nervous system, 71–74, 73fcerebellum, 74–79, 75f, 76fextrapyramidal system, 67–70, 68f, 70fpyramidal system, 65–67, 65f, 67f

Muscle spindles, 56Myelin, 35

NNeocerebellum lesions, 79Neostriatum, 7, 8Nerve deafness, 101Nerve fibers, 19Neural crest, 26

migration of cells of, 26–27, 27f–28fclinical significance of, 28

114 INDEX

Neural plate, 23Neural tube, 28–29

derivatives of vesicles, 30fprimary brain vesicles, 29fsecondary brain vesicles, 30f

Neural tube wall, 31Neuron, 32–33

bipolar, 32, 34fmultipolar, 32, 34fparts of, 36, 37fpseudounipolar, 33, 34f

Neurotransmitters, 49Nissl substance (rER), 36, 37fNodes of Ranvier, 35Nodose ganglia, 90Notochord, 25Nucleus proprius, 53Nucleus solitarius, 90Nystagmus, 97

OOccipitotemporal cortex, 97Olfaction, 87–89, 87f–88fOlfactory bulbs, 31Olfactory nerve, 88Olfactory placodes, 31Olfactory receptor cells, 89Olfactory tract, 88Oligodendrocyte, 33, 35fOlivocerebellar tract, 74Optic chiasm, 95Optic disk, 91Optic nerve, 91, 93, 94f, 95, 96Optic radiations, 6, 95Optic tract, 95Organ of Corti, 101Orientation terms, 1, 1fOropharyngeal membrane, 25Otic ganglion, 72Otic placodes, 31

PPacinian corpuscles, 18, 18f, 59,

60fPaleocerebellum lesions, 79Pallidum, 8Papez circuit, 84, 84fPapilledema, 96Parabrachial nucleus, 90Parahippocampal gyrus, 83Paravertebral ganglia, 71Parieto-occipital cortex, 97Parkinson disease, 72Pelvic splanchnic nerves, 72

Perineurium, 36Periosteal layer, 40Peripheral nerves, 19–20, 21fPeripheral nervous system (PNS), 17Peripheral receptors, 17–18, 18fPerivascular space, 38Petrosal ganglia, 90Photoreceptors, 91, 92Pineal gland, 11Plexuses, 22Pons, 15, 15fPontocerebellar fibers, 74Posterior column pathways, 59, 60fPosterior cranial fossa, 4Posterior ramus, spinal nerve, 22Posterior spinocerebellar tract, 56,

58f, 74Posterior thoracic nucleus, 56Posterior trigeminothalamic tract, 62Posterolateral fissure, 16Posterolateral tract, 53Postganglionic parasympathetic fibers,

72Prepiriform cortex, 89Prevertebral ganglia, 71Primary auditory cortex, 102Primary fissure, 16Primary somatosensory cortex, 54,

55fPrimary visual cortex, 96Primitive node, 25Principal sensory nucleus, 61f, 62Pterygopalatine ganglia, 72Pyramidal system, 65–67Pyramids, 15

RReceptor cell, 88Red nucleus, 78, 79Restiform body, 74Reticular formation, 53Retina, 91–93, 94fRetrograde, 36Rods, 92Ruffini corpuscle, 18, 18f

SSaccadic movements, 97Saccule, 105Sacral splanchnic nerve, 71Schwann cell, 33, 35fSemicircular canals, 104, 104f, 105Semilunar/Gasserian ganglion, 63Sensory decussation, 5, 60f

INDEX 115

Septal area, 82, 85Sigmoid sinus, 40Slow pursuit movements, 97Smell. See OlfactionSomatosensation, types of, 51Somatosensory system, 51

body, 51–59head, 59–3three-neuron chain, 51

Spinal bifida, 26Spinal border cells, 56Spinal cord, 23, 24f

cervical enlargement, 23, 24fdevelopment of, 31, 31flumbar enlargement, 23, 24fmeninges and spaces around, 42,

43fveins of, 47f, 48vessels of, 48

Spinal epidural space, 42, 43Spinal nerves, 20–22Spinal trigeminal nucleus, 61f, 62Spinal trigeminal tract, 61f, 62Spiral ganglion, 101Straight sinus, 40Striatum, 8Stroke, 48Subarachnoid cisterns, 38Subarachnoid space, 38Subdural space, 38Submandibular ganglia, 72Substantia gelatinosa, 53Substantia nigra pars compacta, 8Sulcus limitans, 32Superior cerebellar peduncle, 56, 57fSuperior colliculus, 15, 16f, 54, 67,

93, 97Superior olivary nucleus, 102Superior petrosal sinus, 41Superior sagittal sinus, 38Superior salivatory, 72Supporting cell, 88Sympathetic trunk, 71Synapse, 49

TTaste. See GustationTectum, 15Tentorial incisure/notch, 40Thalamic fasciculus, 8Thalamus, 10, 11, 12f, 16fThoracic nerve, 71Trigeminal motor nucleus, 63Trigeminal nerve, 15Trigeminal sensory system, 59, 61–6,

61fTrigeminocerebellar tract, 74Trigone of lateral ventricle, 45Trochlear nerve, 15Tufted cells, 88

UUpper motor neuron (UMN), 65Utricle, 105

VVagal nerve, 15Ventral forebrain, 82Ventral posteromedial (VPM) nucleus,

90Ventricles, 43–44Vestibular ganglion, 105Vestibular nuclei, 16f, 105Vestibular system, 104–106, 104fVestibulocerebellar fibers, 74Vestibulocochlear nerve, 15, 99, 101,

102Vestibulo-ocular reflex, 106, 106fVisual association cortex, 97Visual deficits, 96Visual processing, 97Visual system, 91

pathways, 93, 95–96structures, 91–93

WWernicke’s area, 4White matter fiber pathways, 7White rami communicantes, 71

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