Nervous System

Histology of the Nervous System

• Types of cells in the nervous tissue.– Neurons– Glial cells or neuroglias support cells.

• CNS: astrocyte (control chemical enviroment), oligodendrocyte (myelination), microglia (phagocyte), ependimal cells (production of CSF)

• PNS: Shwann cells (myelination) and satellite cells.

Neuroglia

(a) Astrocyte

(d) Oligodendrocyte

(e) Sensory neuron with Schwann cells and satellite cells

(b) Microglial cell

(c) Ependymal cells

Schwann cells(forming myelin sheath)

Cell bodyof neuron

Satellite cells

Nerve fiber

Capillary

Neuron

Nerve fibers

Myelin sheath

Process ofoligodendrocyte

Fluid-filled cavity

Brain or spinal cord tissue

Neuron Anatomy

• Major parts:– Cell body (grey matter) or Soma

• Central Nervous System (CNS): clusters = nuclei; in Peripheral Nervous system (PNS) = ganglia

– Neuron processes (axons): • CNS: tracts• PNS: nerves

– Neurofibrils: cytoskeleton– Nissle bodies: RER that is chomatophilic– Dendrites: processes that carry impulses towards the cell body.– Axons: processes that carry impulses away from the cell body.– Axon Hillock– Axon terminals– Synaptic cleft– Myelin fibers (not all the axons)

Structures of a motor neuron

(b)

(a)

Dendrites(receptiveregions)

Cell body(biosynthetic centerand receptive region)

Nucleolus

Nucleus

Terminal branches(telodendria)

Nissl bodies

Axon(impulse generatingand conductingregion)

Axon terminals(secretorycomponent)

Axon hillock

Neurilemma(sheath ofSchwann)

Node of Ranvier

Impulsedirection

Schwann cell(one inter-node)

Neuron cell body

Dendriticspine

Structure of a synapse

Synaptic vesiclescontaining neurotransmitter molecules

Axon of presynapticneuron

Synapticcleft

Ion channel(closed)

Ion channel (open)

Axon terminal of presynaptic neuron

PostsynapticmembraneMitochondrion

Ion channel closed

Ion channel open

Neurotransmitter

Receptor

Postsynapticmembrane

Degradedneurotransmitter

Na+

Na+

Ca2+

Action Potential

1

2

34

5

Myelinated fibers

– Made by:• Oligodendrocytes in CNS• Schwann cells in PNS

– Structures:• Myelin sheath• Neurilemma: sheath of Schwann cells.• Nodes of Ranvier

Myelination of axons in the PNS by Schwann cells

(a)

(b)

(c)

(d)

Schwann cellcytoplasm

Axon

NeurilemmaMyelinsheath

Schwann cellnucleus

Schwanncell plasmamembrane

Myelin sheath

Schwann cellcytoplasm

Neurilemma

Axon

Activity 1

• Identify the parts of a neuron in a slide.

• Identify the parts of a neuron in a model

Neuron Classification

• By structure– Unipolar neurons: 1 process

• Sensory neurons, impulse CNS

– Bipolar neurons: 2 processes• Part of receptor system: eye, ear, olfactory

– Multipolar neurons: several processes.• Impulse CNS

– Activity 2: identify different neurons in the slide.

Neuron classification by their structure

Neuron Classification

• Classification by function– Sensory– Afferent– Association

Classification of neurons by function

Afferentfiber

Efferentfibers

Extensorinhibited

Flexorstimulated

Right arm(site of stimulus)

Left arm (site ofreciprocal activation)

Arm movements

Interneurons

Key:+ Excitatory synapse– Inhibitory synapse

Efferentfibers

Flexorinhibited

Extensorstimulated

+

–+

–

+

+

Flexes

Extends

Structure of a nerve

(a)

(b)

Fascicle

Perineurium Blood vessels

Endoneurium Nerve fibers

Axon

Endoneurium

Perineurium

Epineurium

Myelin sheath

Bloodvessels

Fascicle

Neurophysiology

• How action potentials trigger nervous impulses.– Resting potential– Action potential

• Depolarization of the membrane.

– Refractory period– Repolarization of the membrane– Stimuli transmission

Measuring membrane potential in neurons

Voltmeter

Microelectrodeinside cell

Plasmamembrane

Ground electrodeoutside cell

Neuron

Axon

The basis of the resting membrane potential

Na+ Na+

K+

K+

K+

K+

Na+

Na+

Na+

Na+

Cell interiorNa+

15 mMK+

150 mMCl–

10 mM A–

100 mMNa+

150 mMA–

0.2 mM

Cell exterior

K+

5 mM Cl–

120 mM

Cellexterior

Cellinterior

Plasmamembrane

Na+–K+

pumpDif

fusi

on

K+ N

a+ D

iffus

ion

-70 mV

Changes in membrane potential produced by a depolarizing graded potential

Distance (a few mm)

–70Resting potential

Active area(site of initialdepolarization)

Mem

bra

ne

po

ten

tial

(m

V)

Refractory periods in an AP

Stimulus

Mem

bra

ne

po

ten

tial

(m

V)

Time (ms)

–70

0

+30

0 1 2 3 4 5

Absolute refractoryperiod

Relative refractoryperiod

Depolarization(Na+ enters)

Repolarization(K+ leaves)

After-hyperpolarization

Propagation of an action potential (AP)

–70

+30

(a) Time = 0 ms (b) Time = 2 ms (c) Time = 4 ms

Voltageat 2 ms

Voltageat 4 ms

Voltageat 0 ms

Resting potential

Peak of action potential

Hyperpolarization

Me

mb

ran

e p

ote

nti

al

(mV

))

Relationship between stimulus strength and action potential frequency

Time (ms)

Vo

ltag

eM

emb

ran

e p

ote

nti

al (

mV

)

–70

0

+30

Threshold

Actionpotentials

Stimulusamplitude

Saltatory conduction in a myelinated axon

Node of Ranvier

Cell bodyMyelinsheath

Distalaxon

Central nervous system

The nervous system’s functions

Sensory input

Motor output

Integration

Levels of organization in the nervous systemCentral nervous system (CNS) Brain and spinal cord Integrative and control centers

Sensory (afferent) division Somatic and visceral sensory nerve fibers Conducts impulses from receptors to the CNS

Motor (efferent) division Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands)

Autonomic nervous system (ANS) Visceral motor (involuntary) Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands

Sympathetic division Mobilizes body systems during activity

Parasympathetic division Conserves energy Promotes housekeeping functions during rest

Peripheral nervous system (PNS) Cranial nerves and spinal nerves Communication lines between the CNS and the rest of the body

Somatic nervous System Somatic motor (voluntary) Conducts impulses from the CNS to skeletal muscles

= Structure= Function

Key:

Centralnervoussystem(CNS)

= Sensory (afferent)division of PNS= Motor (efferent)division of PNS

Key: Brain

SpinalcordSkin

Visceral organ

Skeletalmuscle

Peripheral nervous system(PNS)

Motor fiber ofsomatic nervoussystem

Somatic sensoryfiber

Sympatheticmotor fiber of ANS

Parasympatheticmotor fiber of ANS

Visceralsensory fiber

(a)

(b)

Gross Anatomy of the Brain and Cranial Nerves

1. Human Brain (activity 1,2)A. Cerebral Hemispheres of the cerebrumB. DiencephalonC. Brain StemD. Cerebellum

2. MeningesA. Cerebrospinal Fluid– Choroid processes (ependymal cells + capillaries)

3. Cranial Nerves (activity 3)4. Spinal cord5. Brain dissection

A. Cerebrum:Cerebral Hemispheres

• Mainly grey matter (soma of neurons)• 5 lobes

– Frontal: anterior to the Central sulcus– Parietal: posterior to the central sulcus, superior to the

lateral sulcus, superior to the parietal-occipital sulcus– Temporal: inferior to the lateral sulcus, – Occipital: inferior to the parietal-occipital sulcus– Insula (within the lateral sulcus, covered by the

temporal and parietal lobes)

Arrangement of gray and white matter in the CNS

CerebrumCerebellum

Migratorypattern ofneurons

Cortex ofgray matter

Inner graymatter

Gray matter

Outer whitematter

Centralcavity

Central cavity

Inner graymatter

Gray matter

Outer whitematter

Central cavity

Inner graymatter

Outer whitematter

Region of cerebellum

Brain stem

Spinal cord

Lobes and fissures of the cerebral hemispheres

(a)

(b)

Postcentral gyrus

Central sulcus

Precentral gyrus

Frontal lobe Parietal lobe

Parieto-occipital sulcus (on medial surfaceof hemisphere)

Lateral sulcus

Transversecerebral fissure

Occipital lobe

Temporal lobe

Cerebellum

Medulla oblongata

Spinal cord

Cortex(gray matter)

Fissure(a deep sulcus)

Gyrus

Sulcus

White matter

Central sulcusFrontal lobe

Temporal lobe(pulled down)

Gyri of insula

Pons

Lobes and fissures of the cerebral hemispheres

(c)

Parietal lobe

Frontal lobe

RightCerebralhemisphere Occipitallobe

Left cerebralhemisphere

Cerebral veinsand arteriescovered byarachnoid

Longitudinalfissure

Posterior

Anterior

Functional and structural areas of the cerebral cortex

• Primary somatosensory cortex: post central gyrus

• Somatosensory association area: immediate after PSC

• Primary motor area– Broca’s area: speech– Prefontral area: intellect, personality

Functional and structural areas of the cerebral cortex

(a)

Primary motor area

Premotor cortex

Frontaleye field

Working memoryfor spatial tasks

Executive area fortask management

Working memory for object-recall tasks

Broca's area(outlined by dashes)

Solving complex,multitask problems

Prefrontal cortex

Central sulcus

Primary somatosensorycortex

Somatosensoryassociation area

Somatic sensation

Gustatory cortex(in insula)

Taste

Wernicke's area(outlined by dashes)

Primary visualcortex

Visualassociation area

Vision

Auditoryassociation area

Primary auditory cortex

Hearing

1147

4544

8

6 43 1 2

5

43

7

19 1817

224241

22

(b)

Frontal eye field

Prefrontalcortex

Processes emotionsrelated to personaland social interactions

Olfactory bulb

Orbitofrontalcortex

Olfactory tract

Fornix

Temporal lobe

Corpuscallosum

Premotorcortex Primary

motor areaCingulategyrus

Central sulcus

Primary somatosensorycortex

Parietal lobe

Parieto-occipitalsulcus

Somatosensoryassociation area

Occipitallobe

Visual associationarea

Calcarine sulcus

Parahippocampalgyrus

Uncus

Primary olfactorycortex

Primaryvisual cortex

Functional and structural areas of the cerebral cortex

8

1-36

8

6 4

45

7

19

18

181734

28

Thumb

Motor and sensory areas of the cerebral cortex (homuculus)

GenitalsToes

Swallowing

Tongue

Jaw

Motor cortex(precentral gyrus)

Motor Sensory

Le

gLips

Face

NeckBrowEye

FingersH

andW

ristE

lbo

w

Arm

Sh

ou

lder

Tru

nk

Hip

Kn

ee

Hip

Tru

nk

Ne

ck

Hea

d

Arm

Elb

owFo

rear

mH

and

Fing

ers

Thum

b

Eye

Nose

Face

Lips

Teeth

Gums

Jaw

Tongue

Pharynx

Intra-abdominal

B. Basal ganglia (nuclei)

• Islands of grey matter within the white matter.• Flank lateral and third ventricle.• Function: Subcortical motor nuclei

(extrapyramidal system), regulates voluntary motor control.

• Caudate nucleus (memory, love?), lentiform nucleus, putamen (learning reinforcement), globus pallidus.

• Corona radiata: projection of fibers.

Basal nuclei

(a)

Fibers ofcorona radiata

Corpusstriatum

Internal capsule(projection fibersrun deep to lentiform nucleus)

Caudatenucleus

Lentiformnucleus

Thalamus

Tail of caudatenucleus

Basal nuclei

(b)

Corpus callosumAnterior hornof lateral ventricleCaudate nucleus

Third ventriclePutamen Lentiform

nucleusGlobus pallidus

Thalamus

Cerebral cortex

Cerebral white matter

Anterior

Posterior

Inferior hornof lateral ventricle

C. Diencephalon

• Embryologically, part of the forebrain• Major structures:

– Thalamus– Hypothalamus/Pituitary gland– Epithalamus

• Trigunium habenulae• Pineal body• Posterior commussire

– Pretectum (pupilary light relfex)

• Externally– Olfactory, optic tracts, optic nerves, optic chiasma, pituitary

gland, mammilary bodies (part of the limbic system; emotions, long term memory, etc).

Midsagittal section of the brain illustrating the diencephalon and brain stem,

Parietal lobe ofcerebral hemisphere

Corpus callosum

Choroid plexusOccipital lobe ofcerebral hemisphereThalamus(encloses third ventricle)

Pineal body/gland(part of epithalamus)

Posterior commissure

Corporaquadrigemina

Cerebralaqueduct

Arbor vitae

Fourth ventricle

Choroid plexus

Cerebellum

Septum pellucidum

Interthalamicadhesion(intermediatemass of thalamus)

Frontal lobeof cerebralhemisphere

Interventricularforamen

Anteriorcommissure

Hypothalamus

Optic chiasma

Pituitary gland

Temporal lobe ofcerebral hemisphere

Mammillary body

Pons

Medulla oblongata

Spinal cord

Midbrain

Fornix

D. Brain Stem

• Major structures:– Cerebral peduncles– Pons– Medulla oblongata– Decussation of pyramids

Ventral aspect of the human brain, showing the three regions of the brain stem

Frontal lobe

Olfactory bulb(synapse pointof cranial nerve I)

Optic chiasma

Optic nerve (II)

Optic tract

Mammillary body

Pons

Temporal lobe

Medulla

Cerebellum

Spinal cord

Midbrain

E. Cerebellum

• Features:– Center midline: vermis– Arbor vitae “tree of life”

• Function:– Balance and equilibrium

Anterior view

Posterior view

2. Meninges

• Three connective tissue membranes that protect the brain and the medulla from mechanical stress.

• Inflammation of this tissue membrane is called meningitis. If infected, it produces encephalitis.

Meninges

(a)

Superiorsagittal sinus

Skin of scalp

Periosteum

Falx cerebri(in longitudinalfissure only)

Bloodvessel

Arachnoid villus

Pia materArachnoid mater

Duramater

MeningealPeriosteal

Subduralspace

Subarachnoidspace

Bone of skull

Meninges

(b)

Occipital lobe

Superiorsagittal sinus

Dura mater

Tranversesinus

Temporalbone

Scalp

Skull

Tentoriumcerebelli

Cerebellum

Arachnoid materover medullaoblongata

Falx cerebri

Tentorium cerebelli

Superiorsagittal sinus

Straightsinus

Crista galli of theethmoid bone

Cavernoussinus

Internal carotidartery

Falx cerebelli

Partitioning folds of dura mater in the cranial cavity

A. Cerebrospinal fluid

• Fluid, similar in composition to blood plasma, is circulated through the ventricles (cisternas).

• Function: mechanical stress protection of the brain and medulla, acting as a cushion.

• Produced in the choroid plexuses.– Capillary knots in the surface of the ventricles.

Formation, location, and circulation of CSFSuperiorsagittal sinus

Arachnoidvillus

Subarachnoid spaceArachnoid materMeningeal dura materPeriosteal dura materGreat cerebral vein

Tentorium cerebelliStraight sinusConfluence of sinuses

Cerebellum

Choroid plexusCerebral vesselsthat supplychoroid plexus

Central canalof spinal cordSpinal dura mater

Inferior end ofspinal cord

Filum terminale(inferior endof pia mater)

Superiorcerebral vein

Choroid plexusCerebrum coveredwith pia mater

Septumpellucidum

Corpuscallosum

Interventricularforamen

Third ventriclePituitary gland

Cerebral aqueduct

Lateral aperture

Fourth ventricleMedian aperture

(b)

4. Spinal cord

• Location: from C1-C2 (continuation of the brain stem) to the conus medullaris (L1-L2).

• Characteristics: – Protected by the meninges (S1-S2 to the filum

terminale).– Attaches to the vertebras by the denticulate ligaments

of the pia mater and the filum termiale (coccygeal canal)

• Function: association and communication center. Central point of the reflex arc.

Spinal cord external anatomyCervicalnervesC1– C8

ThoracicnervesT1– T12

LumbarnervesL1– L5

SacralnervesS1– S5

Coccygealnerve

C0

Cervical plexus

Intercostalnerves

Cervicalenlargement

Lumbarenlargement

Cauda equina

Brachial plexus

Lumbar plexus

Sacral plexus

Conus medullaris

Filum terminale

Structure of the Spinal Cord

(a)

Dorsal rootganglion

Gray matter

White matterVentral root

Dorsal root

Dorsal and ventralrootlets of spinal nerveDorsal ramus

of spinal nerve

Ventral ramusof spinal nerve

Sympathetic trunk(chain) ganglion

Spinal nerve

Rami communicantes

Histology of the Spinal cord

• Grey matter: H form– Ventral (anterior) horns

• Ventral root (motor)

– Dorsal (posterior) horns• Dorsal roots (sensory)• Dorsal ganglions

– Lateral horn (thoraxic and lumbar region)

• White matter

Organization of the gray matter of the spinal cord

Somatic sensory neuron

Dorsal root(sensory)

Dorsal rootganglion

Visceral sensoryneuron

Somatic motor neuron

Spinal nerve Ventral root (motor) Ventral horn(motor neurons)

Dorsal horn (interneurons)

Visceral motorneuron

SSVS

VM

SM

Funiculus: fiber tracts with the same origin, terminus and function

Transversal section of the Spinal Cord

Transversal sections of the spinal cord

3. Cranial Nerves

• Part of the PNS

• Mnemonic: On ocassion, our trusty truck acts funny-very good vehicle anyhow.

Location and function of cranial nerves

(a)

Frontal lobe

Temporal lobe

Infundibulum

Facialnerve (VII)Vestibulo-cochlearnerve (VIII)

Glosso-pharyngeal nerve (IX)Vagus nerve (X)

Accessory nerve (XI)

Hypoglossal nerve (XII)

Filaments ofolfactory nerve (I)Olfactory bulb

Olfactory tract

Optic nerve (II)

Optic chiasma

Optic tract

Oculomotornerve (III)Trochlearnerve (IV)Trigeminalnerve (V)

Abducensnerve (VI)

Cerebellum

Medulla

Sheep brain dissection

• Identify the following structures– Ventral:

• Olfactory bulb• Optic nerve• Mammilary body• Cerebral peduncle• Cranial nerves• Medulla oblongata

– Dorsal• Cererbum• Cerebellum

Sheep brain dissection– Sagital section

• Cerebral hemisphere• Corpus callosum• Frontal lobe of the cerebellum• Intermedate mass of the cerebellum• Cerebral peduncle• Optical quiasma• Parietal lobe• Cerebellum• Pineal body• Arbor Vitae• Corpora quadrigema• Fourth ventricle• Medulla oblongata• Pons

Sheep brain dissection

– Frontal section of the brain• Fornix• Corpus triatum• Amygdaloid nucleus• Third ventricle• Lateral ventricle• Intermediate mass of the thalamus• Thalamic nuclei• hypothalamus

Relationship of the brain stem and the diencephalon

(a)

Optic chiasma

Floor of hypothalamus

Mammillary body

Trochlear nerve (IV)

Pons

Middle cerebellar peduncle

Hypoglossal nerve (XII)

Pyramid

Decussation ofpyramids

Spinalcord

Optic nerve

Thalamus

Optic tract

Infundibulum(pituitary removed)

Oculomotor nerve (III)Crus cerebri of cerebral peduncles (midbrain)

Trigeminal nerve (V)

Abducens nerve (VI)

Facial nerve (VII)

Vestibulocochlear nerve (VIII)

Glossopharyngeal nerve (IX)

Vagus nerve (X)

Accessory nerve (XI)

Ventral rootof first cervicalnerveVentral view

Relationship of the brain stem and the diencephalon

(b)

Thalamus

Optic tract

Crus cerebri of cerebral peduncles (midbrain)

Trigeminal nerve (V)

Abducens nerve (VI)

Facial nerve (VII)

Vestibulocochlear nerve (VIII)

Glossopharyngeal nerve (IX)

Vagus nerve (X)

Infundibulum

Pituitary gland

Pons

Olive

Hypoglossalnerve (XII)

Accessory nerve (XI)

Superior colliculus

Inferior colliculus

Trochlear nerve (IV)

Superior cerebellar peduncle

Middle cerebellarpeduncle

Inferior cerebellarpeduncle

Fasciculus gracilis

Fasciculus cuneatus

Left lateral view

Relationship of the brain stem and the diencephalon

(c)

Posterior median sulcus

Choroid plexus(fourth venticle)

Pineal gland

Lateral geniculatenucleusMedial geniculatenucleus

Anterior wall offourth ventricle

Fasciculus cuneatus

Fasciculus gracilis

Third ventricle

Thalamus

Superiorcolliculus

Midbrain

Inferiorcolliculus

Trochlear (IV) nerve

Superior cerebellar peduncle

Middle cerebellar peduncle Pons

Inferior cerebellar peduncle

Facial (VII) nerve

Vestibulocochlear (VIII) nerve

Glossopharyngeal (IX) nerve

Vagus (X) nerve

Accessory (XI) nerve

Posterior (dorsal) rootof first cervical nerve

Medulla

Corporaquadrigeminaof tectum

Dorsal view