mosby items and derived items © 2007, 2003 by mosby, inc.slide 1 chapter 13 central nervous system

Mosby items and derived items © 2007, 2003 by Mosby, Inc.

Chapter 13Chapter 13Central Nervous SystemCentral Nervous System


Coverings of the Brain Coverings of the Brain and Spinal Cord and Spinal Cord

• Two protective coverings (Figure 13-2):Two protective coverings (Figure 13-2):

Outer covering is bone; cranial bones encase the Outer covering is bone; cranial bones encase the brain, and vertebrae encase the spinal cord brain, and vertebrae encase the spinal cord (Figure 13-1)(Figure 13-1)

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


Coverings of the Brain Coverings of the Brain and Spinal Cordand Spinal Cord

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

and inner periosteum of the cranial bones; has three important and inner periosteum of the cranial bones; has three important extensionsextensions

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

hemisphereshemispheres

Dural sinuses—function as veins, collecting blood from brain tissues for Dural sinuses—function as veins, collecting blood from brain tissues for return to the heartreturn 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

Arachnoid mater—delicate, cobwebby layer between the dura Arachnoid mater—delicate, cobwebby layer between the dura mater and pia matermater and pia mater



• Meninges—three membranous layers (cont.)Meninges—three membranous layers (cont.)

Pia mater—innermost, transparent layer; adheres Pia mater—innermost, transparent layer; adheres to the outer surface of the brain and spinal cord; to the outer surface of the brain and spinal cord; contains blood vessels; beyond the spinal cord, contains blood vessels; beyond the spinal cord, forms a slender filament called filum terminale; at forms a slender filament called filum terminale; at level of sacrum, blends with dura mater to form a level of sacrum, blends with dura mater to form a fibrous cord that disappears into the periosteum of fibrous cord that disappears into the periosteum of the coccyxthe coccyx



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 Epidural space—located between the dura mater and inside the bony covering of the spinal cord; contains a supporting cushion bony covering of the spinal cord; contains a supporting cushion of fat and other connective tissues (virtually absent around of fat and other connective tissues (virtually absent around brain because dura is continuous with periosteum of bone)brain because dura is continuous with periosteum of bone)

• Subdural space—located between the dura mater and Subdural space—located between the dura mater and arachnoid mater; contains lubricating serous fluidarachnoid mater; contains lubricating serous fluid

• Subarachnoid space—located between the arachnoid and pia Subarachnoid space—located between the arachnoid and pia mater; contains a significant amount of cerebrospinal fluidmater; contains a significant amount of cerebrospinal fluid


Cerebrospinal FluidCerebrospinal Fluid

• FunctionsFunctions

Provides a supportive, protective cushionProvides a supportive, protective cushion

Reservoir of circulating fluid, which is monitored by the brain Reservoir of circulating fluid, which is monitored by the brain to detect changes in the internal environmentto detect changes in the internal environment

• Fluid spacesFluid spaces

Cerebrospinal fluid—found within the subarachnoid space Cerebrospinal fluid—found within the subarachnoid space around the brain and spinal cord and within the cavities and around the brain and spinal cord and within the cavities and canals of the brain and spinal cordcanals of the brain and spinal cord



• Fluid spaces (cont.)Fluid spaces (cont.) Ventricles—fluid-filled spaces within the brain; four Ventricles—fluid-filled spaces within the brain; four

ventricles within the brain (Figure 13-4)ventricles within the brain (Figure 13-4)

• First and second ventricles (lateral)—one located in each First and second ventricles (lateral)—one located in each hemisphere of the cerebrumhemisphere of the cerebrum

• Third ventricle—thin, vertical pocket of fluid below and Third ventricle—thin, vertical pocket of fluid below and medial to the lateral ventriclesmedial to the lateral ventricles

• Fourth ventricle—tiny, diamond-shaped space where the Fourth ventricle—tiny, diamond-shaped space where the cerebellum attaches to the back of the brainstemcerebellum attaches to the back of the brainstem



• Formation and circulation of cerebrospinal Formation and circulation of cerebrospinal fluid (Figure 13-5)fluid (Figure 13-5)

Occurs by separation of fluid from blood in the Occurs by separation of fluid from blood in the choroid plexuseschoroid plexuses

• Fluid from the lateral ventricles seeps through the Fluid from the lateral ventricles seeps through the interventricular foramen (of Monro) into the third ventricleinterventricular foramen (of Monro) into the third ventricle

• From the third ventricle, fluid goes through the cerebral From the third ventricle, fluid goes through the cerebral aqueduct into the fourth ventricleaqueduct into the fourth ventricle



• Formation and circulation of cerebrospinal fluid Formation and circulation of cerebrospinal fluid (cont.)(cont.)

• From the fourth ventricle, fluid goes to two different areas:From the fourth ventricle, fluid goes to two different areas:

Some fluid flows directly into the central canal of the spinal cordSome fluid flows directly into the central canal of the spinal cord

Some fluid leaves the fourth ventricle through openings in its roof Some fluid leaves the fourth ventricle through openings in its roof into the cisterna magna, a space that is continuous with the into the cisterna magna, a space that is continuous with the subarachnoid spacesubarachnoid 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 foramen Lies within the spinal cavity and extends from the foramen magnum to the lower border of the first lumbar vertebramagnum to the lower border of the first lumbar vertebra

Oval cylinder that tapers slightly from above downwardOval cylinder that tapers slightly from above downward

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

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


Spinal CordSpinal Cord

• Structure of the spinal cord (cont.)Structure of the 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 neurons make Dorsal root ganglion—cell bodies of unipolar, sensory neurons make

up a small region of gray matter in the dorsal nerve rootup a small region of gray matter in the dorsal 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 matter of the Cell bodies of multipolar, motor neurons are in the gray matter of the

spinal cordspinal cord

Interneurons are located in the spinal cord’s gray matter coreInterneurons are located in the spinal cord’s gray matter core Spinal nerve—a single mixed nerve on each side of the spinal Spinal nerve—a single mixed nerve on each side of the spinal

cord where the dorsal and ventral nerve roots join togethercord where the dorsal and ventral nerve roots join together



• Structure of the spinal cord (cont.)Structure of the spinal cord (cont.) Cauda equina—bundle of nerve roots extending (along with the Cauda equina—bundle of nerve roots extending (along with the

filum terminale) from the conus medullaris (inferior end of spinal filum terminale) from the conus medullaris (inferior end of spinal cord) (Figure 13-7)cord) (Figure 13-7)

Gray matterGray matter

• Columns of gray matter extend the length of the cordColumns of gray matter extend the length of the cord

• Consists predominantly of cell bodies of interneurons and motor neuronsConsists predominantly of cell bodies of interneurons and motor neurons

• In transverse section, looks like an H with the limbs being called the anterior, In transverse section, looks like an H with the limbs being called the anterior, posterior, and lateral horns of gray matter; cross-bar of H is the gray commissureposterior, and lateral horns of gray matter; cross-bar of H is the gray commissure

White matterWhite matter

• Surrounds the gray matter and is subdivided in each half of the cord into three Surrounds the gray matter and is subdivided in each half of the cord into three funiculi: anterior, posterior, and lateral white columnsfuniculi: anterior, posterior, and lateral white columns

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

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



• Functions of the spinal cordFunctions of the spinal cord

Provides conduction routes to and from the brainProvides conduction routes to and from the brain

• Ascending tracts—conduct impulses up the cord to the brainAscending tracts—conduct impulses up the cord to the brain

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

• Bundles of axons compose all tractsBundles of axons compose all tracts

• Tracts are both structural and functional organizations Tracts are both structural and functional organizations of nerve fibers:of nerve fibers:

Structural—all axons of any one tract originate in the same Structural—all axons of any one tract originate in the same structure and terminate in the same structurestructure and terminate in the same structure

Functional—all axons that compose one tract serve one general Functional—all axons that compose one tract serve one general functionfunction



• Functions of the spinal cord (cont.)Functions of the spinal cord (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—touch related to visual reflexesSpinotectal—touch related to visual reflexes



• Functions of the spinal cord (cont.)Functions of the spinal cord (cont.)

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

side of the bodyside of the body

Anterior corticospinal tracts—voluntary movements on same side of bodyAnterior corticospinal tracts—voluntary movements on same side of body

Reticulospinal tracts—maintain posture during movementReticulospinal tracts—maintain posture during movement

Rubrospinal tracts—transmit impulses that coordinate body movements Rubrospinal tracts—transmit impulses that coordinate body movements and maintenance of postureand maintenance of posture

Tectospinal tracts—head and neck movements during visual reflexesTectospinal tracts—head and neck movements during visual reflexes

Vestibulospinal tracts—coordination of posture and balanceVestibulospinal tracts—coordination of posture and balance

• Spinal cord—reflex center for all spinal reflexes; spinal reflex Spinal cord—reflex center for all spinal reflexes; spinal reflex centers are located in the gray matter of the cordcenters are located in the gray matter of the cord


The Brain The Brain

• 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 A few centimeters in length and separated from the pons above by a horizontal groovehorizontal 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 reticular formation networkcalled the reticular 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


The BrainThe Brain

• 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

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

brainbrain

• Composed of white tracts and reticular formationComposed of white tracts and reticular formation

• Extending divergently through the midbrain are cerebral peduncles; conduct Extending divergently through the midbrain are cerebral peduncles; conduct impulses between the midbrain and cerebrumimpulses between the midbrain and cerebrum

• Corpora quadrigemina—landmark in midbrainCorpora quadrigemina—landmark in midbrain Made up of two inferior colliculi and two superior colliculiMade up of two inferior colliculi and two superior colliculi Forms the posterior, upper part of the midbrain that lies just above the cerebellumForms the posterior, upper part of the midbrain that lies just 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 of neurons involved in Red nucleus and substantia nigra—clusters of cell bodies of neurons involved in muscular controlmuscular control


The BrainThe Brain

• Functions of the brainstemFunctions of the brainstem Performs sensory, motor, and reflex functionsPerforms sensory, motor, and reflex functions

Spinothalamic tracts—important sensory tracts Spinothalamic tracts—important sensory tracts that pass through the brainstemthat pass through the brainstem

Fasciculi cuneatus and gracilis and spinoreticular Fasciculi cuneatus and gracilis and spinoreticular tracts—sensory tracts whose axons terminate in tracts—sensory tracts whose axons terminate in the gray matter of the brainstemthe gray matter of the brainstem

Corticospinal and reticulospinal tracts—two of the Corticospinal and reticulospinal tracts—two of the major tracts present in the white matter of the major tracts present in the white matter of the brainstembrainstem


The BrainThe Brain

• Functions of the brainstem (cont.)Functions of the brainstem (cont.)

Nuclei in medulla—contain reflex centersNuclei in medulla—contain reflex centers

• Of primary importance—cardiac, vasomotor, and respiratory Of primary importance—cardiac, vasomotor, and respiratory centerscenters

• Nonvital reflexes—vomiting, coughing, sneezing, etc.Nonvital reflexes—vomiting, coughing, sneezing, etc.

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

Midbrain—contains centers for certain cranial nerve reflexesMidbrain—contains centers for certain cranial nerve reflexes


The BrainThe Brain

• 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)


The BrainThe Brain• Structure of the cerebellum (cont.)Structure of the cerebellum (cont.)

Consists of the cerebellar hemispheres and the vermisConsists of the cerebellar hemispheres and the vermis Internal white matter—composed of short and long tractsInternal white matter—composed of short and long tracts

• Shorter tracts—conduct impulses from neuron cell bodies located in the cerebellar Shorter tracts—conduct impulses from neuron cell bodies located in the cerebellar cortex to neurons whose dendrites and cell bodies compose nuclei located in the interior cortex to neurons whose dendrites and cell bodies compose nuclei located in the interior of the cerebellumof the cerebellum

• Longer tracts—conduct impulses to and from the cerebellum; fibers enter or leave by Longer tracts—conduct impulses to and from the cerebellum; fibers enter or leave by way of three pairs of pedunclesway of three pairs of peduncles

Inferior cerebellar peduncles—composed chiefly of tracts entering the cerebellum from the Inferior cerebellar peduncles—composed chiefly of tracts entering the cerebellum from the medulla and cordmedulla and cord

Middle cerebellar peduncles—composed almost entirely of tracts entering the cerebellum from Middle cerebellar peduncles—composed almost entirely of tracts entering the cerebellum from the ponsthe pons

Superior cerebellar peduncles—composed principally of tracts leading from dentate nuclei in Superior cerebellar peduncles—composed principally of tracts leading from dentate nuclei in the cerebellum through the red nucleus of the midbrain to the thalamusthe cerebellum through the red nucleus of the midbrain to the thalamus

Dentate nucleiDentate nuclei• Important pair of cerebellar nuclei, one of which is located in each hemisphereImportant pair of cerebellar nuclei, one of which is located in each hemisphere• Nuclei connected with thalamus and with motor areas of the cerebral cortex by tractsNuclei connected with thalamus and with motor areas of the cerebral cortex by tracts• By means of the tracts, cerebellar impulses influence the motor cortex, and the motor By means of the tracts, cerebellar impulses influence the motor cortex, and the motor

cortex influences the cerebellumcortex influences the cerebellum


The BrainThe Brain

• Functions of the cerebellumFunctions of the cerebellum Cerebellum compares the motor commands of the cerebrum to the Cerebellum compares the motor commands of the cerebrum to the

information coming from proprioceptors in the muscle; impulses travel information coming from proprioceptors in the muscle; impulses travel from the cerebellum to both the cerebrum and muscles to coordinate from the cerebellum to both the cerebrum and muscles to coordinate movements to produce the intended action (Figure 13-12)movements to produce the intended action (Figure 13-12)

General functionsGeneral functions

• Acts with cerebral cortex to produce skilled movements by coordinating Acts with cerebral cortex to produce skilled movements by coordinating the activities of groups of musclesthe activities of groups of muscles

• Controls skeletal muscles to maintain balanceControls skeletal muscles to maintain balance

• Controls posture; operates at subconscious level to smooth movements Controls posture; operates at subconscious level to smooth movements and make movements efficient and coordinatedand make movements efficient and coordinated

• Processes sensory information; complements and assists various Processes sensory information; complements and assists various functions of the cerebrumfunctions of the cerebrum


The BrainThe Brain

• 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 ventricle: Consists of several structures located around the third ventricle: thalamus, hypothalamus, optic chiasma, pineal gland, and several thalamus, hypothalamus, optic chiasma, pineal gland, and several othersothers

ThalamusThalamus

• Dumbbell-shaped mass of gray matter made up of many nucleiDumbbell-shaped mass of gray matter made up 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 the Intermediate mass—extends through the third ventricle and joins the two lateral massestwo 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; located in posterior region of each lateral comprising the thalamus; located in posterior region of each lateral mass; play role in processing auditory and visual inputmass; play role in processing auditory and visual input


The BrainThe Brain

Thalamus (cont.)Thalamus (cont.)

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

• Performs the following primary functions:Performs the following primary functions:

Plays two parts in mechanism responsible for sensations:Plays two parts in mechanism responsible for sensations:

– Impulses produce conscious recognition of the crude, less critical sensations of Impulses produce conscious recognition of the crude, less critical sensations of pain, temperature, and touchpain, temperature, and touch

– Neurons relay all kinds of sensory impulses, except possibly olfactory, to the Neurons relay all kinds of sensory impulses, except possibly olfactory, to the cerebrumcerebrum

Plays part in the mechanism responsible for emotions by associating Plays part in the mechanism responsible for emotions by associating sensory impulses with feeling of pleasantness and unpleasantnesssensory impulses with feeling of pleasantness and unpleasantness

Plays part in arousal mechanismPlays part in arousal mechanism

Plays part in mechanisms that produce complex reflex movementsPlays part in mechanisms that produce complex reflex movements


The BrainThe Brain

• Diencephalon (cont.)Diencephalon (cont.) HypothalamusHypothalamus

• Consists of several structures that lie beneath the thalamusConsists of several structures that lie beneath the thalamus

• Forms floor of the third ventricle and lower part of lateral wallsForms floor of the third ventricle and lower part of lateral walls

• Prominent structures found in the hypothalamusProminent structures found in the hypothalamus Supraoptic nuclei—gray matter located just above and on either Supraoptic nuclei—gray matter located just above and on either

side of the optic chiasmaside of the optic chiasma

Paraventricular nuclei—located close to the wall of the third Paraventricular nuclei—located close to the wall of the third ventricleventricle

Mamillary bodies—posterior part of hypothalamus, involved Mamillary bodies—posterior part of hypothalamus, involved with olfactory sensewith olfactory sense


The BrainThe Brain

Hypothalamus (cont.)Hypothalamus (cont.)

• Infundibulum—the stalk leading to the posterior lobe Infundibulum—the stalk leading to the posterior lobe of the pituitary glandof the pituitary 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


The BrainThe Brain

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

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


The BrainThe Brain

• Diencephalon (cont.)Diencephalon (cont.)

Pineal glandPineal gland

• Located just above the corpora quadrigemina of the midbrainLocated just above the corpora quadrigemina of the midbrain

• Involved in regulating the body’s biological clock (Figure 13-14)Involved in regulating the body’s biological clock (Figure 13-14)

• Produces melatonin as a “timekeeping hormone”Produces melatonin as a “timekeeping hormone”

Melatonin is made from the neurotransmitter serotoninMelatonin is made from the neurotransmitter serotonin

Melatonin levels increase when sunlight is absent and decreases Melatonin levels increase when sunlight is absent and decreases when sunlight is present, thus regulating the circadian (daily) when sunlight is present, thus regulating the circadian (daily) biological clock (Figure 13-15)biological clock (Figure 13-15)

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


The BrainThe Brain

• 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 hemisphere is right and left cerebral hemispheres; each hemisphere is divided into five lobes (Figure 13-16):divided into five lobes (Figure 13-16):

Frontal lobeFrontal lobe

Parietal lobeParietal lobe

Temporal lobeTemporal lobe

Occipital lobeOccipital lobe

Insula (island of Riel)Insula (island of Riel)


The BrainThe Brain

Cerebral cortex (cont.)Cerebral cortex (cont.)

• Cerebral cortex—outer surface made up of six layers of Cerebral cortex—outer surface made up 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 postcentral gyrus, cingulate gyrus, and hippocampal gyrusgyrus

• Sulci—shallow groovesSulci—shallow grooves


The BrainThe Brain

Cerebral cortex (cont.)Cerebral cortex (cont.)

• Fissures—deeper grooves, divide each cerebral Fissures—deeper grooves, divide each cerebral hemisphere into lobes; four prominent cerebral fissureshemisphere into lobes; four prominent cerebral fissures

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


The BrainThe Brain

• Structure of the cerebrum (cont.)Structure of the cerebrum (cont.)

Cerebral tracts and basal nucleiCerebral tracts and basal nuclei

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

Caudate nucleusCaudate nucleus

Lentiform nucleus—consists of putamen and pallidumLentiform nucleus—consists of putamen and pallidum

Amygdaloid nucleusAmygdaloid nucleus


The BrainThe Brain

• Structure of the cerebrum (cont.) Structure of the cerebrum (cont.) Cerebral tracts and basal nuclei (cont.)Cerebral tracts and basal nuclei (cont.)

• Cerebral tracts make up cerebrum’s white matter; there Cerebral tracts make up cerebrum’s white matter; there are three types (Figure 13-17):are three types (Figure 13-17):

Projection tracts—extensions of the sensory spinothalamic Projection tracts—extensions of the sensory spinothalamic tracts and motor corticospinal tractstracts and motor corticospinal tracts

Association tracts—most numerous cerebral tracts; extend Association tracts—most numerous cerebral tracts; extend from one convolution to another in the same hemispherefrom one convolution to another in the same hemisphere

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; compose the corpus callosum and anterior and posterior compose the corpus callosum and anterior and posterior commissurescommissures

• Corpus striatum—composed of caudate nucleus, internal Corpus striatum—composed of caudate nucleus, internal capsule, and lentiform nucleuscapsule, and lentiform nucleus


The BrainThe Brain

• Functions of the cerebral cortexFunctions of the cerebral cortex

Functional areas of the cortex—certain areas of the cerebral Functional areas of the cortex—certain areas of the cerebral cortex predominantly engage in one particular function cortex predominantly engage in one particular function (Figures 13-19 and 13-20)(Figures 13-19 and 13-20)

• Postcentral gyrus—mainly general somatic sensory area; Postcentral gyrus—mainly general somatic sensory area; receives impulses from receptors activated by heat, cold, and receives impulses from receptors activated by heat, cold, and touch stimulitouch stimuli

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

• Transverse gyrus—primary auditory areaTransverse gyrus—primary auditory area

• Occipital lobe—primary visual areasOccipital lobe—primary visual areas


The BrainThe Brain

• Functions of the cerebral cortex (cont.)Functions of the cerebral cortex (cont.)

Sensory functions of the cortexSensory functions of the cortex

• Somatic senses—sensations of touch, pressure, temperature, Somatic senses—sensations of touch, pressure, temperature, proprioception, and similar perceptions that require complex sensory proprioception, and similar perceptions that require complex sensory organsorgans

• Cortex contains a “somatic sensory map” of the bodyCortex contains a “somatic sensory map” of the body

• Information sent to primary sensory areas is relayed to sensory Information sent to primary sensory areas is relayed to sensory association areas, as well as to other parts of the brainassociation areas, as well as to other parts of the brain

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


The BrainThe Brain

Motor functions of the cortexMotor functions of the cortex

• For normal movements to occur, many parts of the nervous For normal movements to occur, many parts of the nervous system must functionsystem must function

• Precentral gyrus—primary somatic motor area; controls Precentral gyrus—primary somatic motor area; controls individual musclesindividual muscles

• Secondary motor area—in the gyrus immediately anterior to Secondary motor area—in the gyrus immediately anterior to the precentral gyrus; activates groups of muscles the precentral gyrus; activates groups of muscles simultaneouslysimultaneously


The BrainThe Brain Integrative functions of the cortexIntegrative functions of the cortex

• Consciousness (Figure 13-21)Consciousness (Figure 13-21) State of awareness of one’s self, one’s environment, and other beingsState of awareness of one’s self, one’s environment, and other beings Depends on excitation of cortical neurons by impulses conducted to them Depends on excitation of cortical neurons by impulses conducted to them

by the reticular activating systemby the reticular activating system There are two current concepts about the reticular activating system:There are two current concepts about the reticular activating system:

– Functions as the arousal system for the cerebral cortexFunctions as the arousal system for the cerebral cortex

– Its functioning is crucial for maintaining consciousnessIts functioning is crucial for maintaining consciousness

• LanguageLanguage Ability to speak and write words and ability to understand spoken and written Ability to speak and write words and ability to understand spoken and written

wordswords Speech centers—areas in the frontal, parietal, and temporal lobesSpeech centers—areas in the frontal, parietal, and temporal lobes Left cerebral hemisphere contains speech centers in approximately 90% Left cerebral hemisphere contains speech centers in approximately 90%

of the population; in the remaining 10%, contained in either the right of the population; in the remaining 10%, contained in either the right hemisphere or bothhemisphere or both

Aphasias—caused by lesions in speech centersAphasias—caused by lesions in speech centers


The BrainThe Brain Integrative functions of the cortex (cont.)Integrative functions of the cortex (cont.)

• Emotions (Figure 13-22)Emotions (Figure 13-22) Subjective experiencing and objective expressing of emotions involve Subjective experiencing and objective expressing of emotions involve

functioning of the limbic systemfunctioning of the limbic system Limbic system—also known as the “emotional brain”Limbic system—also known as the “emotional brain”

– Most structures of limbic system lie on the medial surface of the cerebrum; they are Most structures of limbic system lie on the medial surface of the cerebrum; they are the cingulate gyrus and the hippocampusthe cingulate gyrus and the hippocampus

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

• MemoryMemory One of the major human mental activitiesOne of the major human mental activities Cortex is capable of storing and retrieving both short- and Cortex is capable of storing and retrieving both short- and

long-term memorylong-term memory Temporal, parietal, and occipital lobes are among the areas responsible for Temporal, parietal, and occipital lobes are among the areas responsible for

short- and long-term memoryshort- and long-term memory Engrams—structural traces in the cerebral cortex that comprise long-term Engrams—structural traces in the cerebral cortex that comprise long-term

memoriesmemories Cerebrum’s limbic system plays a key role in memoryCerebrum’s limbic system plays a key role in memory


The BrainThe Brain

Hemisphericity—specialization of cerebral hemispheresHemisphericity—specialization of cerebral hemispheres

• Right and left hemispheres of the cerebrum specialize in Right and left hemispheres of the cerebrum specialize in different functions; however, both sides of a normal person’s different functions; however, both sides of a normal person’s brain communicate with each other to accomplish complex brain communicate with each other to accomplish complex functionsfunctions

• Left hemisphere is responsible for the following:Left hemisphere is responsible for the following: Language functionsLanguage functions

Dominating control of certain hand movementsDominating control of certain hand movements

• Right hemisphere is responsible for the following:Right hemisphere is responsible for the following: Perception of certain kinds of auditory materialPerception of certain kinds of auditory material

Tactual perceptionTactual perception

Perceiving and visualizing spatial relationshipsPerceiving and visualizing spatial relationships


Somatic Sensory Pathways Somatic Sensory Pathways in the Central Nervous System in the Central Nervous System

• For the cerebral cortex to perform its sensory functions, For the cerebral cortex to perform its sensory functions, impulses must first be conducted to the sensory areas impulses must first be conducted to the sensory areas by sensory pathways (Figure 13-24)by sensory pathways (Figure 13-24)

• Three main pools of sensory neurons:Three main pools of sensory neurons: Primary sensory neurons—conduct impulses from the periphery Primary sensory neurons—conduct impulses from the periphery

to the central nervous systemto the central nervous system Secondary sensory neuronsSecondary sensory neurons

• Conduct impulses from cord or brainstem to thalamusConduct impulses from cord or brainstem to thalamus

• Dendrites and cell bodies are located in gray matter of cord and brainstemDendrites and cell bodies are located in gray matter of cord and brainstem

• Axons ascend in ascending tracts up cord and through the brainstem, and terminate Axons ascend in ascending tracts up cord and through the brainstem, and terminate in thalamus, where they synapse with dendrites or cell bodies of tertiary sensory in thalamus, where they synapse with dendrites or cell bodies of tertiary sensory neuronsneurons

Tertiary sensory neuronsTertiary sensory neurons• Conduct impulses from thalamus to the postcentral gyrus of parietal lobeConduct impulses from thalamus to the postcentral gyrus of parietal lobe

• Bundle of axons of tertiary sensory neurons form thalamocortical tractsBundle of axons of tertiary sensory neurons form thalamocortical tracts

• Extend through internal capsule to cerebral cortexExtend through internal capsule to cerebral cortex


Somatic Sensory Pathways Somatic Sensory Pathways in the Central Nervous Systemin the Central Nervous System

• Sensory pathways to the cerebral cortex are crossedSensory pathways to the cerebral cortex are crossed

• Two sensory pathways conduct impulses that Two sensory pathways conduct impulses that produce sensations of touch and pressure:produce 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 touch Functions—transmit impulses that produce discriminating touch and pressure sensations and kinesthesiaand pressure sensations and kinesthesia

Spinothalamic pathway—functions are crude touch and Spinothalamic pathway—functions are crude touch and pressure sensationspressure sensations


Somatic Motor Pathways Somatic Motor Pathways in the Central Nervous Systemin the Central Nervous System

• For the cerebral cortex to perform its motor functions, For the cerebral cortex to perform its motor functions, impulses are conducted from its motor areas to skeletal impulses are conducted from its motor areas to skeletal muscles by somatic motor pathwaysmuscles by somatic motor pathways

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

• Principle of the final common path—cardinal principle Principle of the final common path—cardinal principle about somatic motor pathways; only one final common about somatic motor pathways; only one final common path, the motor neuron from the anterior gray horn of the path, the motor neuron from the anterior gray horn of the spinal cord, conducts impulses to skeletal musclesspinal cord, conducts impulses to skeletal muscles


Somatic Motor Pathways Somatic Motor Pathways in the Central Nervous Systemin the Central Nervous System

• Two methods used to classify somatic motor pathways:Two methods used to classify somatic motor pathways: Divides pathways into pyramidal and extrapyramidal tracts (Figure 13-25)Divides pathways into pyramidal and extrapyramidal tracts (Figure 13-25)

• Pyramidal tracts—also known as corticospinal tractsPyramidal tracts—also known as corticospinal tracts Approximately three quarters of the fibers decussate in the medulla and extend down Approximately three quarters of the fibers decussate in the medulla and extend down

the cord in the crossed corticospinal tract located on the opposite side of the spinal the cord in the crossed corticospinal tract located on the opposite side of the spinal cord in the lateral white columncord in the lateral white column

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

• Extrapyramidal tracts—much more complex than pyramidal tractsExtrapyramidal tracts—much more complex than pyramidal tracts Consist of all motor tracts from the brain to the spinal cord anterior horn motor Consist of all motor tracts from the brain to the spinal cord anterior horn motor

neurons except the corticospinal tractsneurons except the corticospinal tracts Within the brain, consist of numerous relays of motor neurons between motor areas Within the brain, consist of numerous relays of motor neurons between motor areas

of cortex, basal nuclei, thalamus, cerebellum, and brainstemof cortex, basal nuclei, thalamus, cerebellum, and brainstem Within the spinal cord, some important tracts are the reticulospinal tractsWithin the spinal cord, some important tracts are the reticulospinal tracts Conduction by extrapyramidal tracts plays a crucial part in producing large, Conduction by extrapyramidal tracts plays a crucial part in producing large,

automatic movementsautomatic movements Conduction by extrapyramidal tracts plays an important part in emotional Conduction by extrapyramidal tracts plays an important part in emotional

expressionsexpressions Motor program—set of coordinated commands that control the programmed motor Motor program—set of coordinated commands that control the programmed motor

activity mediated by extrapyramidal pathways (Figure 13-26)activity mediated by extrapyramidal pathways (Figure 13-26)


Cycle of Life: Cycle of Life: Central Nervous SystemCentral Nervous System

• The development and degeneration of the central The development and degeneration of the central nervous system is the most obvious functional change nervous system is the most obvious functional change over the life spanover the life span

• Development of the brain and spinal cord begins Development of the brain and spinal cord begins in the wombin the womb

• Lack of development in the newborn is evidenced by Lack of development in the newborn is evidenced by lack of complex integrative functionslack of complex integrative functions LanguageLanguage

Complex memoryComplex memory

Comprehension of spatial relationshipsComprehension of spatial relationships

Complex motor skillsComplex motor skills


Cycle of Life: Cycle of Life: Central Nervous SystemCentral Nervous System

• Complex functions develop by adulthoodComplex functions develop by adulthood

• Late adulthood—tissues degenerateLate adulthood—tissues degenerate

Profound degeneration—unable to perform Profound degeneration—unable to perform complex functionscomplex functions

Milder degeneration—temporary memory lapse or Milder degeneration—temporary memory lapse or difficulty with complex motor tasksdifficulty with complex motor tasks


The Big Picture: The Central Nervous The Big Picture: The Central Nervous System and the Whole Body System and the Whole Body

• Central nervous system—ultimate regulator of Central nervous system—ultimate regulator of the body; essential to survivalthe body; essential to survival

• Able to integrate bits of information from all Able to integrate bits of information from all over the body, make sense of them, and over the body, make sense of them, and make decisionsmake decisions

mosby items and derived items © 2007, 2003 by mosby, inc.slide 1 chapter 13 central nervous system

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