Chapter 13: Central Nervous System. COVERINGS OF THE BRAIN AND SPINAL CORD Two protective coverings (Figure 13-2) Outer covering is bone; cranial bones

Chapter 13: Central Chapter 13: Central Nervous SystemNervous System

COVERINGS OF THE BRAIN COVERINGS OF THE BRAIN AND SPINAL CORDAND SPINAL CORD

Two protective coverings (Figure 13-2)Two protective coverings (Figure 13-2) Outer covering is bone; cranial bones encase Outer covering is bone; cranial bones encase

the brain and vertebrae encase the spinal the brain and vertebrae encase the spinal cord (Figure 13-1)cord (Figure 13-1)

Inner covering is the meninges; the meninges Inner covering is the meninges; the meninges of the cord continue inside the spinal cavity of the cord continue inside the spinal cavity beyond the end of the spinal cordbeyond the end of the spinal cord

COVERINGS OF THE BRAINCOVERINGS OF THE BRAINAND SPINAL CORD: MENINGESAND SPINAL CORD: MENINGES

Meninges have three membranous layers (Figure Meninges have three membranous layers (Figure 13-3)13-3) Dura mater: strong, white, fibrous tissue; outer layer of Dura mater: strong, white, fibrous tissue; outer layer of

meninges and inner periosteum of the cranial bones; has meninges and inner periosteum of the cranial bones; has three important extensionsthree important extensions

• Falx cerebriFalx cerebri Projects downward into the longitudinal fissure between the Projects downward into the longitudinal fissure between the

two cerebral hemispherestwo cerebral hemispheres Dural sinuses: function as veins, collecting blood from brain Dural sinuses: function as veins, collecting blood from brain

tissues for return to the hearttissues for return to the heart Superior sagittal sinus—one of several dural sinusesSuperior sagittal sinus—one of several dural sinuses

• Falx cerebelli: separates the two hemispheres of the cerebellumFalx cerebelli: separates the two hemispheres of the cerebellum• Tentorium cerebelli: separates the cerebellum from the cerebrumTentorium cerebelli: separates the cerebellum from the cerebrum

COVERINGS OF THE BRAIN AND COVERINGS OF THE BRAIN AND SPINAL CORD: MENINGES (cont.)SPINAL CORD: MENINGES (cont.)

Meninges have three membranous layers (cont.)Meninges have three membranous layers (cont.) Arachnoid mater: delicate, cobweblike layer between the Arachnoid mater: delicate, cobweblike layer between the

dura mater and pia materdura mater and pia mater Pia mater: innermost, transparent layer; adheres to the Pia mater: innermost, transparent layer; adheres to the

outer surface of the brain and spinal cord; contains outer surface of the brain and spinal cord; contains blood vessels; beyond the spinal cord, forms a slender blood vessels; beyond the spinal cord, forms a slender filament called filament called filum terminalefilum terminale

Several spaces exist between and around the meningesSeveral spaces exist between and around the meninges• Epidural space: located between the dura mater and inside the bony Epidural space: located between the dura mater and inside the bony

covering of the spinal cord; contains a supporting cushion of fat and covering of the spinal cord; contains a supporting cushion of fat and other connective tissues (virtually absent around brain because dura is other connective tissues (virtually absent around brain because dura is continuous with periosteum of bone)continuous with periosteum of bone)

• Subdural space: located between the dura mater and arachnoid mater; Subdural space: located between the dura mater and arachnoid mater; contains lubricating serous fluidcontains lubricating serous fluid

• Subarachnoid space: located between the arachnoid and pia mater; Subarachnoid space: located between the arachnoid and pia mater; contains a significant amount of cerebrospinal fluid (CSF)contains a significant amount of cerebrospinal fluid (CSF)

CEREBROSPINAL FLUIDCEREBROSPINAL FLUID FunctionsFunctions

Provides a supportive, protective cushionProvides a supportive, protective cushion Reservoir of circulating fluid monitored by the brain to detect Reservoir of circulating fluid monitored by the brain to detect

changes in the internal environmentchanges in the internal environment Fluid spacesFluid spaces

CSF: found within the subarachnoid space around the brain CSF: found within the subarachnoid space around the brain and spinal cord and within the cavities and canals of the brain and spinal cord and within the cavities and canals of the brain and spinal cordand spinal cord

Ventricles: four fluid-filled spaces within the brain (Figure 13-4)Ventricles: four fluid-filled spaces within the brain (Figure 13-4)• First and second ventricles (lateral): one located in each hemisphere of First and second ventricles (lateral): one located in each hemisphere of

the cerebrumthe cerebrum• Third ventricle: thin, vertical pocket of fluid below and medial to the Third ventricle: thin, vertical pocket of fluid below and medial to the

lateral ventricleslateral ventricles• Fourth ventricle: tiny, diamond-shaped space where the cerebellum Fourth ventricle: tiny, diamond-shaped space where the cerebellum

attaches to the back of the brainstemattaches to the back of the brainstem

CEREBROSPINAL FLUID (cont.)CEREBROSPINAL FLUID (cont.)

Formation and circulation of CSF (Figure 13-5)Formation and circulation of CSF (Figure 13-5) Occurs by separation of fluid from blood in the choroid Occurs by separation of fluid from blood in the choroid

plexusesplexuses• Fluid from the lateral ventricles seeps through the interventricular Fluid from the lateral ventricles seeps through the interventricular

foramen (of Monro) into the third ventricleforamen (of Monro) into the third ventricle• From the third ventricle fluid goes through the cerebral aqueduct From the third ventricle fluid goes through the cerebral aqueduct

(of Sylvius) into the fourth ventricle(of Sylvius) into the fourth ventricle• From the fourth ventricle fluid goes to two different areasFrom the fourth ventricle fluid goes to two different areas

Some fluid flows directly into the central canal of the spinal Some fluid flows directly into the central canal of the spinal cordcord

Some fluid leaves the fourth ventricle through openings in its Some fluid leaves the fourth ventricle through openings in its roof and goes into the cisterna magna, a space that is roof and goes into the cisterna magna, a space that is continuous with the subarachnoid spacecontinuous with the subarachnoid space

• Fluid circulates in the subarachnoid space and then is absorbed Fluid circulates in the subarachnoid space and then is absorbed into venous blood through the arachnoid villiinto venous blood through the arachnoid villi

SPINAL CORDSPINAL CORD

Structure of the spinal cord (Figure 13-6)Structure of the spinal cord (Figure 13-6) Lies within the spinal cavity and extends from the Lies within the spinal cavity and extends from the

foramen magnum to the lower border of the first foramen magnum to the lower border of the first lumbar vertebralumbar vertebra

Oval-shaped cylinder that tapers slightly from above Oval-shaped cylinder that tapers slightly from above downwarddownward

Two bulges, one in the cervical region and one in the Two bulges, one in the cervical region and one in the lumbar regionlumbar region

Anterior median fissure and posterior median sulcus Anterior median fissure and posterior median sulcus are two deep grooves; anterior fissure is deeper and are two deep grooves; anterior fissure is deeper and widerwider

SPINAL CORD (cont.)SPINAL CORD (cont.)

Nerve rootsNerve roots• Fibers of dorsal nerve rootFibers of dorsal nerve root

Carry sensory information into the spinal canalCarry sensory information into the spinal canal Dorsal root ganglion: cell bodies of unipolar, sensory Dorsal root ganglion: cell bodies of unipolar, sensory

neurons make up a small region of gray matter in the neurons make up a small region of gray matter in the dorsal nerve rootdorsal nerve root

• Fibers of ventral nerve rootFibers of ventral nerve root Carry motor information out of the spinal cordCarry motor information out of the spinal cord Cell bodies of multipolar motor neurons are in the gray Cell bodies of multipolar motor neurons are in the gray

matter of the spinal cordmatter of the spinal cord


Interneurons are located in the spinal cord’s Interneurons are located in the spinal cord’s gray matter coregray matter core

Spinal nerve: a single mixed nerve on each Spinal nerve: a single mixed nerve on each side of the spinal cord where the dorsal and side of the spinal cord where the dorsal and ventral nerve roots join togetherventral nerve roots join together

Cauda equina: bundle of nerve roots Cauda equina: bundle of nerve roots extending (along with the filum terminale) extending (along with the filum terminale) from the conus medullaris (inferior end of from the conus medullaris (inferior end of spinal cord) (Figure 13-7)spinal cord) (Figure 13-7)


Gray matterGray matter• Columns of gray matter extend the length of the Columns of gray matter extend the length of the

cordcord• Consists predominantly of cell bodies of Consists predominantly of cell bodies of

interneurons and motor neuronsinterneurons and motor neurons• In transverse section, looks like an H, with the In transverse section, looks like an H, with the

limbs called the limbs called the anterior, posterioranterior, posterior, and , and lateral lateral horns of gray matter; horns of gray matter; crossbar of H is the crossbar of H is the gray gray commissurecommissure


White matterWhite matter• Surrounds the gray matter and is subdivided in Surrounds the gray matter and is subdivided in

each half on the cord into three funiculi: anterior, each half on the cord into three funiculi: anterior, posterior, and lateral white columnsposterior, and lateral white columns

• Each funiculus consists of a large bundle of axons Each funiculus consists of a large bundle of axons divided into tractsdivided into tracts

• Names of spinal tracts indicate the location of the Names of spinal tracts indicate the location of the tract, the structure in which the axons originate, tract, the structure in which the axons originate, and the structure in which they terminateand the structure in which they terminate


Functions of the spinal cordFunctions of the spinal cord Provides conduction routes to and from the Provides conduction routes to and from the

brainbrain• Ascending tracts conduct impulses up the cord to Ascending tracts conduct impulses up the cord to

the brainthe brain• Descending tracts conduct impulses down the cord Descending tracts conduct impulses down the cord

from the brainfrom the brain• Bundles of axons comprise all tracts Bundles of axons comprise all tracts


Provides conduction routes to and from the Provides conduction routes to and from the brain (cont.)brain (cont.)• Tracts are both structural and functional Tracts are both structural and functional

organizations of nerve fibersorganizations of nerve fibers Structural: all axons of any one tract originate in the Structural: all axons of any one tract originate in the

same structure and terminate in the same structuresame structure and terminate in the same structure Functional: all axons that comprise one tract serve one Functional: all axons that comprise one tract serve one

general functiongeneral function


Provides conduction routes to and from the Provides conduction routes to and from the brain (cont.)brain (cont.)• Important ascending (sensory) tracts (Figure 13-8)Important ascending (sensory) tracts (Figure 13-8)

Lateral spinothalamic tracts: crude touch, pain, and Lateral spinothalamic tracts: crude touch, pain, and temperaturetemperature

Anterior spinothalamic tracts: crude touch, pressureAnterior spinothalamic tracts: crude touch, pressure Fasciculi gracilis and cuneatus: discriminating touch and Fasciculi gracilis and cuneatus: discriminating touch and

conscious kinesthesiaconscious kinesthesia Spinocerebellar tracts: subconscious kinesthesiaSpinocerebellar tracts: subconscious kinesthesia Spinotectal: touchSpinotectal: touch


• Important descending (motor) tracts (Figure 13-8)Important descending (motor) tracts (Figure 13-8) Lateral corticospinal tracts: voluntary movements on Lateral corticospinal tracts: voluntary movements on

opposite side of the bodyopposite side of the body Anterior corticospinal tracts: voluntary movements on Anterior corticospinal tracts: voluntary movements on

same side of bodysame side of body Reticulospinal tracts: maintain posture during movementReticulospinal tracts: maintain posture during movement Rubrospinal tracts: transmit impulses that coordinate Rubrospinal tracts: transmit impulses that coordinate

body movements and maintenance of posturebody movements and maintenance of posture Tectospinal tracts: head and neck movements during Tectospinal tracts: head and neck movements during

visual reflexesvisual reflexes Vestibulospinal tracts: coordination of posture and Vestibulospinal tracts: coordination of posture and

balancebalance• Spinal cord: reflex center for all spinal reflexes, Spinal cord: reflex center for all spinal reflexes,

which are located in the gray matter of the cordwhich are located in the gray matter of the cord

BRAINBRAIN

Structures of the brainstem (Figures 13-9 and 13-10)Structures of the brainstem (Figures 13-9 and 13-10) Medulla oblongataMedulla oblongata

• Lowest part of the brainstemLowest part of the brainstem• Part of the brain that attaches to spinal cord; located just above the Part of the brain that attaches to spinal cord; located just above the

foramen magnumforamen magnum• A few centimeters in length and separated from the pons above by A few centimeters in length and separated from the pons above by

a horizontal groovea horizontal groove• Composed of white matter and a network of gray and white matter Composed of white matter and a network of gray and white matter

called the called the reticular formation networkreticular formation network• Pyramids: two bulges of white matter located on the ventral side of Pyramids: two bulges of white matter located on the ventral side of

the medulla; formed by fibers of the pyramidal tractsthe medulla; formed by fibers of the pyramidal tracts• Olive: oval projection located lateral to the pyramidsOlive: oval projection located lateral to the pyramids• Nuclei: clusters of neuron cell bodies located in the reticular Nuclei: clusters of neuron cell bodies located in the reticular

formationformation

BRAIN (cont.)BRAIN (cont.)

Structures of the brainstem (cont.)Structures of the brainstem (cont.) PonsPons

• Located above the medulla and below the midbrainLocated above the medulla and below the midbrain• Composed of white matter and reticular formationComposed of white matter and reticular formation

BRAIN (cont.)BRAIN (cont.) MidbrainMidbrain

• Located above the pons and below the cerebrum; Located above the pons and below the cerebrum; forms the midsection of the brainforms the midsection of the brain

• Composed of white tracts and reticular formationComposed of white tracts and reticular formation• Extending divergently through the midbrain are Extending divergently through the midbrain are

cerebral peduncles, which conduct impulses cerebral peduncles, which conduct impulses between the midbrain and cerebrumbetween the midbrain and cerebrum

• Corpora quadrigemina: landmark in midbrainCorpora quadrigemina: landmark in midbrain Composed of two inferior colliculi and two superior colliculiComposed of two inferior colliculi and two superior colliculi Forms the posterior, upper part of the midbrain that lies Forms the posterior, upper part of the midbrain that lies

just above the cerebellumjust above the cerebellum Inferior colliculus contains auditory centersInferior colliculus contains auditory centers Superior colliculus contains visual centersSuperior colliculus contains visual centers Red nucleus and substantia nigra: clusters of cell bodies Red nucleus and substantia nigra: clusters of cell bodies

of neurons involved in muscular controlof neurons involved in muscular control

BRAIN (cont.)BRAIN (cont.) Functions of the brainstemFunctions of the brainstem

Performs sensory, motor, and reflex functionsPerforms sensory, motor, and reflex functions Spinothalamic tracts, fasciculi cuneatus and Spinothalamic tracts, fasciculi cuneatus and

gracilis, spinoreticular tracts, corticospinal and gracilis, spinoreticular tracts, corticospinal and reticulospinal tracts pass through brainstemreticulospinal tracts pass through brainstem

Nuclei in medulla contain reflex centersNuclei in medulla contain reflex centers• Of primary importance: cardiac, vasomotor, and Of primary importance: cardiac, vasomotor, and

respiratory centersrespiratory centers• Nonvital reflexes: vomiting, coughing, sneezing, etc.Nonvital reflexes: vomiting, coughing, sneezing, etc.

Pons contains reflexes mediated by fifth, sixth, Pons contains reflexes mediated by fifth, sixth, seventh, and eighth cranial nerves and seventh, and eighth cranial nerves and pneumotaxic centers that help regulate respirationpneumotaxic centers that help regulate respiration

Midbrain contains centers for certain cranial nerve Midbrain contains centers for certain cranial nerve reflexes (visual and auditory)reflexes (visual and auditory)


Structure of the cerebellum (Figure 13-11)Structure of the cerebellum (Figure 13-11) Second largest part of the brain; contains more neurons Second largest part of the brain; contains more neurons

than the rest of the nervous systemthan the rest of the nervous system Located just below the posterior portion of the cerebrum; Located just below the posterior portion of the cerebrum;

transverse fissure separates these two parts of the braintransverse fissure separates these two parts of the brain Gray matter makes up the cortex and white matter Gray matter makes up the cortex and white matter

predominates in the interiorpredominates in the interior Arbor vitae: internal white matter of the cerebellum; Arbor vitae: internal white matter of the cerebellum;

distinctive pattern similar to the veins of a leafdistinctive pattern similar to the veins of a leaf Cerebellum has numerous sulci and delicate, parallel Cerebellum has numerous sulci and delicate, parallel

gyri (folia)gyri (folia) Consists of the cerebellar hemispheres and the vermisConsists of the cerebellar hemispheres and the vermis

BRAIN (cont.)BRAIN (cont.) Structure of the cerebellum (cont.)Structure of the cerebellum (cont.)

Internal white matter: composed of short and long Internal white matter: composed of short and long tractstracts

• Shorter tracts conduct impulses within the cerebellumShorter tracts conduct impulses within the cerebellum• Longer tracts conduct impulses to and from the cerebellum; Longer tracts conduct impulses to and from the cerebellum;

fibers enter or leave by way of three pairs of pedunclesfibers enter or leave by way of three pairs of peduncles Inferior cerebellar peduncles: composed chiefly of tracts Inferior cerebellar peduncles: composed chiefly of tracts

into the cerebellum from the medulla and cordinto the cerebellum from the medulla and cord Middle cerebellar peduncles: composed almost entirely Middle cerebellar peduncles: composed almost entirely

of tracts into the cerebellum from the ponsof tracts into the cerebellum from the pons Superior cerebellar peduncles: composed principally of Superior cerebellar peduncles: composed principally of

tracts from dentate nuclei in the cerebellum through the tracts from dentate nuclei in the cerebellum through the red nucleus of the midbrain to the thalamusred nucleus of the midbrain to the thalamus


Structure of the cerebellum (cont.)Structure of the cerebellum (cont.) Dentate nucleiDentate nuclei

• Important pair of cerebellar nuclei, one of which is Important pair of cerebellar nuclei, one of which is located in each hemispherelocated in each hemisphere

• Nuclei connected with thalamus and motor areas Nuclei connected with thalamus and motor areas of the cerebral cortex by tractsof the cerebral cortex by tracts

• Through the tracts, cerebellar impulses influence Through the tracts, cerebellar impulses influence the motor cortex and the motor cortex influences the motor cortex and the motor cortex influences the cerebellumthe cerebellum

Functions of the CerebellumFunctions of the Cerebellum

Provides involuntary coordination of body Provides involuntary coordination of body movementsmovements

Helps control postureHelps control posture Controls balance and allows body Controls balance and allows body

movements to be smooth and coordinatedmovements to be smooth and coordinated

BRAIN: DIENCEPHALONBRAIN: DIENCEPHALON Diencephalon (Figure 13-13)Diencephalon (Figure 13-13)

Located between the cerebrum and the midbrainLocated between the cerebrum and the midbrain Consists of several structures located around the third Consists of several structures located around the third

ventricle: thalamus, hypothalamus, optic chiasma, pineal ventricle: thalamus, hypothalamus, optic chiasma, pineal gland, and several othersgland, and several others

ThalamusThalamus• Dumbbell-shaped mass of gray matter composed of many nucleiDumbbell-shaped mass of gray matter composed of many nuclei• Each lateral mass forms one lateral wall of the third ventricleEach lateral mass forms one lateral wall of the third ventricle• Intermediate mass extends through the third ventricle and joins Intermediate mass extends through the third ventricle and joins

the two lateral massesthe two lateral masses• Geniculate bodies: two of the most important groups of nuclei Geniculate bodies: two of the most important groups of nuclei

comprising the thalamus; play role in processing auditory and comprising the thalamus; play role in processing auditory and visual inputvisual input

• Serves as a major relay station for sensory impulses on their way Serves as a major relay station for sensory impulses on their way to the cerebral cortexto the cerebral cortex

BRAIN: DIENCEPHALON (cont.)BRAIN: DIENCEPHALON (cont.)

Thalamus (cont.)Thalamus (cont.)• Plays two parts in mechanism responsible for Plays two parts in mechanism responsible for

sensationssensations Impulses produce conscious recognition of the crude, less-Impulses produce conscious recognition of the crude, less-

critical sensations of pain, temperature, and touchcritical sensations of pain, temperature, and touch Neurons relay all kinds of sensory impulses, except Neurons relay all kinds of sensory impulses, except

possibly olfactory, to the cerebrumpossibly olfactory, to the cerebrum• Plays part in the mechanism responsible for Plays part in the mechanism responsible for

emotions by associating sensory impulses with emotions by associating sensory impulses with feeling of pleasantness and unpleasantnessfeeling of pleasantness and unpleasantness

• Plays part in arousal mechanismPlays part in arousal mechanism• Plays part in mechanisms that produce complex Plays part in mechanisms that produce complex

reflex movementsreflex movements


HypothalamusHypothalamus• Consists of several structures that lie beneath the Consists of several structures that lie beneath the

thalamusthalamus• Forms floor of the third ventricle and lower part of lateral Forms floor of the third ventricle and lower part of lateral

wallswalls• Prominent structures found in the hypothalamusProminent structures found in the hypothalamus

Supraoptic nucleiSupraoptic nuclei Paraventricular nucleiParaventricular nuclei Mamillary bodies: posterior part of hypothalamus, Mamillary bodies: posterior part of hypothalamus,

involved with olfactory senseinvolved with olfactory sense• Infundibulum: the stalk leading to the posterior lobe of the Infundibulum: the stalk leading to the posterior lobe of the

pituitary glandpituitary gland• Small but functionally important area of the brain; Small but functionally important area of the brain;

performs many functions of greatest importance for performs many functions of greatest importance for survival and enjoymentsurvival and enjoyment

• Links mind and bodyLinks mind and body• Links nervous system to endocrine systemLinks nervous system to endocrine system


Hypothalamus (cont.)Hypothalamus (cont.)• Summary of hypothalamic functionsSummary of hypothalamic functions

Regulator and coordinator of autonomic activitiesRegulator and coordinator of autonomic activities Major relay station between the cerebral cortex and lower Major relay station between the cerebral cortex and lower

autonomic centers; crucial part of the route by which autonomic centers; crucial part of the route by which emotions express themselves in changed bodily functionsemotions express themselves in changed bodily functions

Synthesizes hormones secreted by posterior pituitary and Synthesizes hormones secreted by posterior pituitary and plays an essential role in maintaining water balanceplays an essential role in maintaining water balance

Some neurons function as endocrine glandsSome neurons function as endocrine glands Plays crucial role in arousal mechanismPlays crucial role in arousal mechanism Crucial part of mechanism regulating appetiteCrucial part of mechanism regulating appetite Crucial part of mechanism maintaining normal body Crucial part of mechanism maintaining normal body

temperaturetemperature


Pineal glandPineal gland• Located just above the corpora quadrigemina of Located just above the corpora quadrigemina of

the midbrainthe midbrain• Involved in regulating the body’s biological clock Involved in regulating the body’s biological clock

(Figure 13-14)(Figure 13-14)• Produces melatonin as a “timekeeping” hormoneProduces melatonin as a “timekeeping” hormone

Melatonin is made from the neurotransmitter serotoninMelatonin is made from the neurotransmitter serotonin Levels increase when sunlight is absent and decrease Levels increase when sunlight is absent and decrease

when sunlight is present, thus regulating the circadian when sunlight is present, thus regulating the circadian (daily) biologic clock (Figure 13-15)(daily) biologic clock (Figure 13-15)

Melatonin is the “sleep hormone”Melatonin is the “sleep hormone”

BRAIN: CEREBRUMBRAIN: CEREBRUM Structure of the cerebrumStructure of the cerebrum

Cerebral cortexCerebral cortex• Largest and uppermost division of the brain; consists of Largest and uppermost division of the brain; consists of

right and left cerebral hemispheres, each divided into five right and left cerebral hemispheres, each divided into five lobes (Figure 13-16)lobes (Figure 13-16)

Frontal lobeFrontal lobe Parietal lobeParietal lobe Temporal lobeTemporal lobe Occipital lobeOccipital lobe Insula (island of Reil)Insula (island of Reil)

• Cerebral cortex: outer surface composed of six layers of Cerebral cortex: outer surface composed of six layers of gray mattergray matter

• Gyri: convolutions; some are named: precentral gyrus, Gyri: convolutions; some are named: precentral gyrus, postcentral gyrus, cingulate gyrus, and hippocampal gyruspostcentral gyrus, cingulate gyrus, and hippocampal gyrus

• Sulci: shallow groovesSulci: shallow grooves

BRAIN: CEREBRUM (cont.)BRAIN: CEREBRUM (cont.)

Cerebral cortex (cont.)Cerebral cortex (cont.)• Fissures: deeper grooves that divide each cerebral Fissures: deeper grooves that divide each cerebral

hemisphere into lobes; four are prominenthemisphere into lobes; four are prominent Longitudinal fissure: deepest fissure; divides cerebrum Longitudinal fissure: deepest fissure; divides cerebrum

into two hemispheresinto two hemispheres Central sulcus (fissure of Rolando): groove between Central sulcus (fissure of Rolando): groove between

frontal and parietal lobesfrontal and parietal lobes Lateral fissure (fissure of Sylvius): groove between Lateral fissure (fissure of Sylvius): groove between

temporal lobe below and parietal lobes above; island of temporal lobe below and parietal lobes above; island of Reil lies deep in lateral fissureReil lies deep in lateral fissure

Parietooccipital fissure: groove that separates occipital Parietooccipital fissure: groove that separates occipital lobe from parietal lobeslobe from parietal lobes


Cerebral tracts and basal nucleiCerebral tracts and basal nuclei• Basal nucleiBasal nuclei

Structure: islands of gray matter located deep inside the Structure: islands of gray matter located deep inside the white matter of each hemisphere (Figure 13-18); include white matter of each hemisphere (Figure 13-18); include the following:the following:

• Caudate nucleusCaudate nucleus• Lentiform nucleus: consists of putamen and Lentiform nucleus: consists of putamen and

pallidumpallidum• Amygdaloid nucleusAmygdaloid nucleus

Function: regulation of voluntary (conscious) motor Function: regulation of voluntary (conscious) motor control related to posture, walking, and other repetitive control related to posture, walking, and other repetitive movements; possible roles in thinking and learningmovements; possible roles in thinking and learning


Cerebral tracts and basal nuclei (cont.)Cerebral tracts and basal nuclei (cont.)• Three types of cerebral tracts make up cerebrum’s Three types of cerebral tracts make up cerebrum’s

white matter (Figure 13-17)white matter (Figure 13-17) Projection tracts: extensions of the sensory Projection tracts: extensions of the sensory

spinothalamic tracts and motor corticospinal tractsspinothalamic tracts and motor corticospinal tracts Association tracts: most numerous cerebral tracts; Association tracts: most numerous cerebral tracts;

extend from one convolution to another in the same extend from one convolution to another in the same hemispherehemisphere

Commissural tracts: extend from one convolution to a Commissural tracts: extend from one convolution to a corresponding convolution in the other hemisphere; corresponding convolution in the other hemisphere; comprise the corpus callosum and anterior and posterior comprise the corpus callosum and anterior and posterior commissurecommissure

BRAIN: CEREBRAL CORTEXBRAIN: CEREBRAL CORTEX

Functions of the cerebral cortexFunctions of the cerebral cortex Certain areas of the cerebral cortex engage in Certain areas of the cerebral cortex engage in

predominantly one particular function (Figures predominantly one particular function (Figures 13-19 and 13-20)13-19 and 13-20)• Postcentral gyrus: mainly general somatic sensory Postcentral gyrus: mainly general somatic sensory

area; receives impulses from receptors activated by area; receives impulses from receptors activated by heat, cold, and touch stimuliheat, cold, and touch stimuli

• Precentral gyrus: chiefly somatic motor area; impulses Precentral gyrus: chiefly somatic motor area; impulses from neurons in this area descend over motor tracts from neurons in this area descend over motor tracts and stimulate skeletal musclesand stimulate skeletal muscles

• Transverse gyrus: primary auditory areaTransverse gyrus: primary auditory area• Occipital lobe: primary visual areaOccipital lobe: primary visual area

BRAIN: CEREBRAL CORTEX BRAIN: CEREBRAL CORTEX (cont.)(cont.)

Sensory functions of the cortexSensory functions of the cortex• Somatic senses: sensations of touch, pressure, Somatic senses: sensations of touch, pressure,

temperature, proprioception, and similar temperature, proprioception, and similar perceptions that require complex sensory organsperceptions that require complex sensory organs

• Cortex contains a somatic sensory map of the bodyCortex contains a somatic sensory map of the body• Information sent to primary sensory areas is Information sent to primary sensory areas is

relayed to sensory association areas and other relayed to sensory association areas and other parts of the brainparts of the brain

• The sensory information is compared and The sensory information is compared and evaluated, and the cortex integrates separate bits evaluated, and the cortex integrates separate bits of information into whole perceptionsof information into whole perceptions

BRAIN: CEREBRAL CORTEX BRAIN: CEREBRAL CORTEX (cont.)(cont.)

Motor functions of the cortexMotor functions of the cortex• For normal movements to occur, many parts of the For normal movements to occur, many parts of the

nervous system must functionnervous system must function• Precentral gyrus: primary somatic motor area; Precentral gyrus: primary somatic motor area;

controls individual musclescontrols individual muscles• Secondary motor area: in the gyrus immediately Secondary motor area: in the gyrus immediately

anterior to the precentral gyrus; activates groups of anterior to the precentral gyrus; activates groups of muscles simultaneouslymuscles simultaneously

Integrative functions of the cortexIntegrative functions of the cortex

CONSCIOUSNESSCONSCIOUSNESS State of awareness of one’s self, one’s State of awareness of one’s self, one’s

environment, and other human beings (Figure environment, and other human beings (Figure 13-21)13-21)

Depends on excitation of cortical neurons by Depends on excitation of cortical neurons by impulses conducted to them by the reticular impulses conducted to them by the reticular activating systemactivating system

Two current concepts about the reticular Two current concepts about the reticular activating systemactivating system Functions as arousal system for the cerebral cortexFunctions as arousal system for the cerebral cortex Functioning is crucial for maintaining consciousnessFunctioning is crucial for maintaining consciousness

LANGUAGELANGUAGE

Ability to speak and write words and Ability to speak and write words and understand spoken and written wordsunderstand spoken and written words

Speech centers: areas in the frontal, Speech centers: areas in the frontal, parietal, and temporal lobesparietal, and temporal lobes

Left cerebral hemisphere contains speech Left cerebral hemisphere contains speech centers in approximately 90% of the centers in approximately 90% of the population; contained in either the right population; contained in either the right hemisphere or both in the remaining 10%hemisphere or both in the remaining 10%

Aphasias: lesions in speech centersAphasias: lesions in speech centers

EMOTIONSEMOTIONS

Subjective experiencing and objective Subjective experiencing and objective expressing of emotions involve functioning of the expressing of emotions involve functioning of the limbic system (Figure 13-22)limbic system (Figure 13-22)

Limbic system: also known as Limbic system: also known as the emotional the emotional brainbrain Most structures of limbic system lie on the medial Most structures of limbic system lie on the medial

surface of the cerebrum (cingulate gyrus and surface of the cerebrum (cingulate gyrus and hippocampus)hippocampus)

Have primary connections with other parts of the Have primary connections with other parts of the brain, such as the thalamus, fornix, septal nuclei, brain, such as the thalamus, fornix, septal nuclei, amygdaloid nucleus, and hypothalamusamygdaloid nucleus, and hypothalamus

MEMORYMEMORY

A major mental activityA major mental activity Cortex is capable of storing and retrieving Cortex is capable of storing and retrieving

both short- and long-term memoryboth short- and long-term memory Temporal, parietal, and occipital lobes are Temporal, parietal, and occipital lobes are

among the areas responsible for short- and among the areas responsible for short- and long-term memorylong-term memory

Structural changes in the neural pathways of Structural changes in the neural pathways of the cerebral cortex store long-term memoriesthe cerebral cortex store long-term memories

Limbic system plays a key role in memoryLimbic system plays a key role in memory

SOMATIC SENSORY PATHWAYS IN SOMATIC SENSORY PATHWAYS IN THE CENTRAL NERVOUS SYSTEMTHE CENTRAL NERVOUS SYSTEM For the cerebral cortex to perform its sensory For the cerebral cortex to perform its sensory

functions, impulses must first be conducted to functions, impulses must first be conducted to the sensory areas by sensory pathways (Figure the sensory areas by sensory pathways (Figure 13-23)13-23)

Three main pools of sensory neuronsThree main pools of sensory neurons Primary sensory neurons conduct impulses from the Primary sensory neurons conduct impulses from the

periphery to the central nervous systemperiphery to the central nervous system Secondary sensory neuronsSecondary sensory neurons

• Conduct impulses from the cord or brainstem to the thalamusConduct impulses from the cord or brainstem to the thalamus• Dendrites and cell bodies are located in the gray matter of the Dendrites and cell bodies are located in the gray matter of the

cord and brainstemcord and brainstem• Axons ascend in tracts up the cord and through the Axons ascend in tracts up the cord and through the

brainstem, terminating in the thalamus, where they synapse brainstem, terminating in the thalamus, where they synapse with dendrites or cell bodies of tertiary sensory neuronswith dendrites or cell bodies of tertiary sensory neurons

SOMATIC SENSORY PATHWAYS IN SOMATIC SENSORY PATHWAYS IN THE CENTRAL NERVOUS SYSTEM THE CENTRAL NERVOUS SYSTEM

(cont.)(cont.) Three main pools of sensory neurons Three main pools of sensory neurons

(cont.)(cont.) Tertiary sensory neuronsTertiary sensory neurons

• Conduct impulses from thalamus to the postcentral Conduct impulses from thalamus to the postcentral gyrus of the parietal lobegyrus of the parietal lobe

• Bundle of axons of tertiary sensory neurons form the Bundle of axons of tertiary sensory neurons form the thalamocortical tractsthalamocortical tracts

• Extend through the internal capsule to the cerebral Extend through the internal capsule to the cerebral cortexcortex

Sensory pathways to the cerebral cortex Sensory pathways to the cerebral cortex are crossedare crossed


(cont.)(cont.) Two sensory pathways conduct impulses that Two sensory pathways conduct impulses that

produce sensations of touch and pressureproduce sensations of touch and pressure Medial lemniscal systemMedial lemniscal system

• Consists of tracts that make up the fasciculi cuneatus and Consists of tracts that make up the fasciculi cuneatus and gracilis, and the medial lemniscusgracilis, and the medial lemniscus

• Axons of secondary sensory neurons make up medial Axons of secondary sensory neurons make up medial lemniscuslemniscus

• Functions: transmit impulses that produce discriminating Functions: transmit impulses that produce discriminating touch and pressure sensations and kinesthesiatouch and pressure sensations and kinesthesia

Spinothalamic pathway: functions are crude touch Spinothalamic pathway: functions are crude touch and pressure sensationand pressure sensation


(cont.)(cont.) For the cerebral cortex to perform its motor For the cerebral cortex to perform its motor

functions, impulses are conducted from its motor functions, impulses are conducted from its motor areas to skeletal muscles by somatic motor areas to skeletal muscles by somatic motor pathwayspathways

Consist of motor neurons that conduct impulses Consist of motor neurons that conduct impulses from the central nervous system to skeletal from the central nervous system to skeletal muscles; some motor pathways are extremely muscles; some motor pathways are extremely complex and others are very simplecomplex and others are very simple

SOMATIC MOTOR PATHWAYS IN THE SOMATIC MOTOR PATHWAYS IN THE CENTRAL NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM

Two methods used to classify somatic motor Two methods used to classify somatic motor pathways: pyramidal and extrapyramidal tracts pathways: pyramidal and extrapyramidal tracts (Figure 13-24)(Figure 13-24) Pyramidal tracts: also known as Pyramidal tracts: also known as corticospinal tractscorticospinal tracts

• Approximately three quarters of the fibers decussate in Approximately three quarters of the fibers decussate in the medulla and extend down the cord in the crossed the medulla and extend down the cord in the crossed corticospinal tract located on the opposite side of the corticospinal tract located on the opposite side of the spinal cord in the lateral white columnspinal cord in the lateral white column

• Approximately one quarter of the fibers do not decussate Approximately one quarter of the fibers do not decussate but extend down the same side of the spinal cord as the but extend down the same side of the spinal cord as the cerebral area from which they camecerebral area from which they came

SOMATIC MOTOR PATHWAYS IN SOMATIC MOTOR PATHWAYS IN THE CENTRAL NERVOUS SYSTEM THE CENTRAL NERVOUS SYSTEM

Extrapyramidal tracts: much more complex than Extrapyramidal tracts: much more complex than pyramidal tractspyramidal tracts• Consist of all motor tracts from the brain to the spinal cord Consist of all motor tracts from the brain to the spinal cord

anterior horn motor neurons except the corticospinal tractsanterior horn motor neurons except the corticospinal tracts• Within the brain, consist of numerous relays of motor Within the brain, consist of numerous relays of motor

neurons between motor areas of the cortex, basal nuclei, neurons between motor areas of the cortex, basal nuclei, thalamus, cerebellum, and brainstemthalamus, cerebellum, and brainstem

• Within the spinal cord, some important tracts are the Within the spinal cord, some important tracts are the reticulospinal tractsreticulospinal tracts

• Conduction by extrapyramidal tracts plays a crucial part in Conduction by extrapyramidal tracts plays a crucial part in producing large, automatic movementsproducing large, automatic movements

• Conduction by extrapyramidal tracts plays an important part Conduction by extrapyramidal tracts plays an important part in emotional expressionsin emotional expressions

• Motor program: set of coordinated commands that control Motor program: set of coordinated commands that control the programmed motor activity mediated by extrapyramidal the programmed motor activity mediated by extrapyramidal pathways (Figure 13-25)pathways (Figure 13-25)

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Chapter 13: Central Nervous System. COVERINGS OF THE BRAIN AND SPINAL CORD Two protective coverings (Figure 13-2) Outer covering is bone; cranial bones