13 the brain and cranial nerves

© 2011 Pearson Education, Inc.

PowerPoint® Lecture Presentations prepared byAlexander G. CheroskeMesa Community College at Red Mountain

13The Brain and Cranial Nerves


Section 1: Functional Anatomy of Brain and Cranial Nerves

• Learning Outcomes• 13.1 Name the major regions of the brain, and

describe their functions.• 13.2 Explain how the brain is protected and

supported, and how cerebrospinal fluid forms and circulates.

• 13.3 List the components of the medulla oblongata and pons, and specify the functions of each.

• 13.4 List the main components of the cerebellum, and specify the functions of each.



• Learning Outcomes• 13.5 List the main components of the midbrain, and specify

the functions of each.

• 13.6 List the main components of the diencephalon, and specify the functions of each.

• 13.7 Identify the main components of the limbic system, and specify the locations and functions of each.

• 13.8 Describe the structure and function of the basal nuclei of the cerebrum.

• 13.9 Identify the major superficial landmarks of the cerebrum, and cite the locations of each.



• Learning Outcomes• 13.10 Identify the locations of the motor, sensory,

and association areas of the cerebral cortex, and discuss the functions of each.

• 13.11 Discuss the significance of the white matter of the cerebral cortex.

• 13.12 CLINICAL MODULE Discuss the origin and significance of the major categories of

brain waves seen in an electroencephalogram.• 13.13 Identify the cranial nerves by name and

number, and cite the functions of each.



• Brain characteristics• Equals ~97% of body’s neural tissue in adults• “Typical” brain

• Weighs 1.4 kg (3 lb)• Has volume of 1200 mL (71 in.3)

• Size varies among individuals• Male are ~10% larger than female

• Owing to differences in overall body size

• No correlation between size and intelligence• Functional normal individuals with smallest (750 mL)

and largest (2100 mL) brains



• Brain development at 4 weeks• Neural tube is present

• Hollow cylinder that is beginning of CNS

• Has internal passageway (neurocoel)• Cephalic portion enlarges into three portions (primary

brain vesicles)1. Prosencephalon (proso, forward + encephalos, brain)

• “Forebrain” is at tip of neural tube

§ Mesencephalon• “Midbrain” is an expansion caudal to prosencephalon

§ Rhombencephalon• “Hindbrain” most caudal portion, continuous with spinal cord


Figure 13 Section 1

A lateral view of the brain of an embryo after4 weeks of development showing the neural tube

Rhombencephalon

Spinalcord

Mesencephalon

Prosencephalon

A lateral view of the brain of a 5-week-old embryo

Prosencephalon Rhombencephalon

Neurocoel

Diencephalon

Telencephalon

Metencephalon Myelencephalon

Spinalcord

Spinal cordCerebellum

Medullaoblongata

Pons

Cerebrum

Diencephalon(covered bycerebrum)

Mesencephalon(covered bycerebrum)

Brain development in a child, showingthe cerebrum covering other portionsof the brain



• Brain development at 5 weeks• Primary brain vesicles change position and

prosencephalon and rhombencencephalon subdivide to form secondary brain vesicles

• Prosencephalon• Diencephalon (dia, through + encephalos, brain)

• Becomes major relay and processing center for information to/from cerebrum

• Telencephalon (telos, end)

• Becomes cerebrum in adult brain



• Brain development at 5 weeks (continued)• Secondary brain vesicles (continued)

• Rhombencephalon• Metencephalon (meta, after)

• Adjacent to mesencephalon

• Forms cerebellum and pons in adult brain

• Myelencephalon (myelon, spinal cord)• Becomes medulla oblongata in adult brain


Module 13.1: Major brain regions

• Major brain regions• Cerebrum

• Divided into pair of large cerebral hemispheres• Surfaces covered by superficial layer of gray

matter• = Cerebral cortex (cortex, rind or bark)

• Functions• Conscious thought

• Memory storage and processing

• Regulation of skeletal muscle contractions



• Superficial cerebral structures• Fissures

• Deep grooves that subdivide hemispheres

• Gyri (singular, gyrus)• Folds in cerebral cortex that increase surface

area

• Sulci (singular, sulcus)• Shallow depressions in cerebral cortex that

separate adjacent gyri



• Cerebellum• Partially hidden by cerebral hemispheres

• Second largest structure of brain

• Functions• Coordination and modulation of motor

commands from cerebral cortex


Figure 13.1 1

A diagrammatic view of the brainshowing its major regions andtheir general functions

Cerebrum

Is divided into a pair of large cerebral hemispheres whose surfaces are covered by asuperficial layer of gray matter called the cerebral cortex

Fissures Gyri Sulci

Spinal cord

Cerebellum

Functions in coordination andmodulation of motor commandsfrom the cerebral cortex

Medulla oblongataPonsMidbrainIncludes threestructures

Brain stem

Diencephalon

Is the structural and functionallink between the cerebralhemispheres and the rest ofthe CNS.

Not visible in this view; thehypothalamus, or floor of thediencephalon

Thalamus



• Diencephalon• Structural and functional link between cerebral

hemispheres and rest of CNS

• Two parts• Thalamus

• Relay and processing centers for sensory information

• Hypothalamus (hypo-, below)• Floor of diencephalon

• Contains centers involved with

• Emotions

• Autonomic function

• Hormone production



• Brain stem (3 parts)1. Midbrain

• Contains nuclei that coordinate visual and auditory reflexes

• Contains centers that help to maintain consciousness

2. Pons (pons, bridge)• Connects cerebellum to brain stem• Has tracts and relay centers• Contains nuclei that function in somatic and

visceral motor control



• Brain stem (3 parts, continued)

3. Medulla oblongata• Relays sensory information to other areas of

brain stem and thalamus

• Contains major centers that regulate autonomic function

• Examples: heart rate, blood pressure

Animation: Brain


Figure 13.1 2

Two views of the ventricles, which are filled with cerebrospinal fluid

Cerebralhemispheres

Cerebralhemispheres

Pons

Medulla oblongata

Spinal cordCentral canal Central canal Cerebellum

Ventricular system, anterior viewVentricular system, lateral view

Fourth ventricle

Aqueduct of midbrain

Third ventricle

Lateral ventricle

Interventricular foramen

Ventricles of the Brain



• Ventricles of the brain• Fluid-filled cavities

• Filled with cerebrospinal fluid• Lined with ependymal cells

• Formed during development as neurocoel expands within cerebral hemispheres, diencephalon, and metencephalon

• Connected by narrow canals



• Four ventricles

1. & 2. Lateral ventricles• Contained within each cerebral hemisphere

• Each connected to third ventricle by interventricular foramen

• Separated medially by septum pellucidum• “Roof” partially formed by thick white matter tract

connecting hemispheres (corpus callosum)

• Then narrows to become central canal of spinal cord



• Four ventricles (continued)

3. Third ventricle• Contained within diencephalon

• Connected to fourth ventricle by aqueduct of the midbrain

4. Fourth ventricle• Begins in metencephalon and extends into

superior portion of medulla oblongata

• Then narrows to become central canal of spinal cord


Figure 13.1 2

Cerebralhemispheres

Pons

Medulla oblongata

Spinal cordCentral canal

Ventricular system, lateral view

Fourth ventricle


Third ventricle

Lateral ventricle




Figure 13.1 2

Cerebralhemispheres

Central canal Cerebellum

Ventricular system, anterior view

Fourth ventricle


Third ventricle

Lateral ventricle




Figure 13.1 3

Lateral ventricles

Interventricularforamen

Third ventricle

Inferior tip oflateral ventricle

Aqueduct ofmidbrain

Fourth ventricle

Central canal

Cerebellum

Septum pellucidum

Corpus callosum

Two views of the ventricles, which are filled with cerebrospinal fluid


Module 13.1 Review

a. Name the major regions of the brain and the distinct structures of each.

b. Describe the role of the medulla oblongata.

c. Compare the corpus callosum to the septum pellucidum.


Module 13.2: Cranial meninges and cerebrospinal fluid

• Cranial meninges1. Dura mater

• Consists of two layers • Separated by slender fluid-filled gap containing fluids

and blood vessels

1. Outer (endosteal) layer

• Fused to cranial bones (no epidural space)

2. Inner (meningeal) layer



• Cranial meninges (continued)

2. Arachnoid mater• Consists of

• Arachnoid membrane

• Provides smooth covering that does not follow brain’s underlying folds

• Subarachnoid space lies below

• Arachnoid trabeculae

• Connect to pia mater



• Cranial meninges (continued)

3. Pia mater• Bound to brain surface by astrocyte processes

• Extends into every fold and accompanies cerebral blood vessels extending into surface brain structures


Figure 13.2 1

The three layers of the cranial meninges:the dura mater, arachnoid mater, and pia mater Subdural space

Cranium(skull)

Arachnoid mater

Arachnoid membrane

Subarachnoid space

Arachnoid trabeculae

Cerebral cortexPia mater

Dura mater

Is bound to the surface of the brain by astrocytes

Dura mater (endosteal layer)

Dural sinusDura mater (meningeal layer)



• Dural folds and sinuses• Dural folds

• Dip into cranial cavity and return• Provide additional stabilization and support to

brain

• Falx cerebri (falx, sickle shaped)• Projects between cerebral hemispheres• Inferior attachment to crista galli (anteriorly) and

internal occipital crest (posteriorly)• Superior and inferior sagittal sinuses lie within



• Dural folds and sinuses (continued)• Dural folds (continued)

• Tentorium cerebelli (tentorium, a tent)• Separates cerebrum from cerebellum

• Falx cerebelli• Separates cerebellar hemispheres along midsagittal

line

• Inferior to tentorium cerebelli


Figure 13.2 2

The dural sinuses and dural folds

Falx cerebri

Falx cerebelli

Tentorium cerebelli

Superior sagittal sinusInferior

sagittal sinus



• Cerebrospinal fluid (CSF)• Completely surrounds and bathes CNS

exposed surfaces

• Materials diffuse between CSF and interstitial fluid of CNS across ependymal walls

• Total volume = ~150 mL• Entire volume replaced in ~8 hours



• Cerebrospinal fluid (continued)• Choroid plexus (choroid, vascular coat;

plexus, network)• Consists of ependymal cells and capillaries

• Produces CSF• ~500 mL/day

• Found in all ventricles



• Cerebrospinal fluid circulation• Created and circulates between ventricles• From fourth ventricle, CSF can circulate

• Down central canal of spinal cord• Out single median aperture and lateral

apertures into subarachnoid space• Down around spinal cord and cauda equina• Up around brain

• Absorbed back into venous circulation through arachnoid granulations within superior sagittal sinus


Figure 13.2 3

Superior sagittal sinus

Third ventricle

Aqueduct of the midbrain

Central canalof spinal cord

Dura mater

Arachnoid

Subarachnoid space

The sites of cerebrospinal fluid production,circulation, and absorption into the venoussystem


Figure 13.2 3

Nutrients,O2

Capillaries

Waste products,CO2

AstrocyteNeuron

Ependymalcells

Choroid plexuscells

Removalof waste

Productionof CSF

Cerebrospinalfluid in

third ventricle

Choroid plexus

The sites of cerebrospinal fluid production, circulation, and absorption into the venous system

Interstitial fluidin thalamus


Figure 13.2 4

Dura mater Superiorsagittal sinus

Cranium

Arachnoidgranulation

CSFmovement

SubduralspaceArachnoidmembrane

Pia materCerebralcortex

An arachnoid granulation, the site at whichcerebrospinal fluid is absorbed into thevenous circulation


Module 13.2 Review

a. From superficial to deep, name the layers that constitute the cranial meninges.

b. What would happen if the normal circulation or reabsorption of CSF became blocked?

c. How would decreased diffusion across the arachnoid granulations affect the volume of cerebrospinal fluid in the ventricles?


Module 13.3: Medulla oblongata and pons

• Medulla oblongata• All communication (sensory and motor) between

brain and spinal cord passes through• Center for coordination of relatively complex

autonomic reflexes and control of visceral functions• Major anatomical features

• Olive (prominent bulge and anterolateral surface)• Pyramids (contain descending/motor tracts from

cerebral cortex)• Some fibers cross over to other side of spinal cord

• = Decussation (decussation, crossing over)


Figure 13.3 1

Structure of the medulla oblongata

The anterior surface ofthe medulla oblongata

PonsPyramids

Site of decussation



• Medulla oblongata components• Autonomic centers (controlling vital functions)

• Reticular formation• Cardiovascular centers• Respiratory rhythmicity center• Solitary nucleus

• Relay stations• Olivary nucleus• Nucleus cuneatus• Nucleus gracilis


Figure 13.3 2

Structure of the medulla oblongataOlive Autonomic centers

Attachment tomembranousroof of fourthventricle

Posteriormedian sulcusSpinal cord

Posterolateral viewAnterior view

Two views of the structureof the medulla oblongatashowing its landmarksand structures

Reticular formationCardiovascular centersRespiratory rhythmicity

centerSolitary nucleus

Olivary nucleusNucleus cuneatusNucleus gracilis

Relay stations


Figure 13.3 2



• Pons• Links cerebellum with midbrain, diencephalon,

cerebrum, medulla oblongata, and spinal cord• Contains:

• Tracts (ascending and descending)• Respiratory centers (pneumotaxic and

apneustic)• Reticular formation

• Loosely organized mass of gray matter containing centers that regulate vital autonomic functions

• Extends from medulla oblongata to mesencephalon


Figure 13.3 3

The pons, which links the cerebellumwith the midbrain, diencephalon,cerebrum, medulla oblongata, andspinal cord

Midbrain

Pons

Medullaoblongata

Spinal cord

Olivary nucleus

Transverse fibers

Ascending tracts Descending tractsTracts Respiratory Centers

Pneumotaxic centerApneustic center

Cerebellum

Fourthventricle

Reticular formation


Module 13.3 Review

a. What is the function of the ascending and descending tracts in the medulla oblongata?

b. Name the medulla oblongata parts that relay somatic sensory information to the thalamus.

c. Describe the pyramids of the medulla oblongata and the result of decussation.


Module 13.4: Cerebellum

• Cerebellum • Is an automatic processing center that

monitors proprioceptive, visual, tactile, balance, and auditory sensations

• Has two primary functions1. Adjusting postural muscles2. Programming and fine-tuning movements

controlled at conscious and subconscious levels• Ataxia (ataxia, lack of order)

• Disturbance of muscular coordination from trauma, stroke, or drugs such as alcohol



• Components (posterior view)• Anterior and posterior lobes

• Separated by primary fissure• Two hemispheres

• Separated by vermis (worm)

• Surface of gray matter (cerebellar cortex)• Contains huge, highly branched Purkinje cells

that form many sensory and motor synapses

• Has folds (folia)


Figure 13.4 1

Structural features of the cerebellum

The posterior, superior surface of the cerebellum

Posterior view

Left Hemisphereof Cerebellum

Right Hemisphereof Cerebellum

Folia

Primary fissure

Vermis

Posterior lobe

Anterior lobe

Cerebellum


Figure 13.4 2

Purkinje cells of the cerebellar cortex

Dendrites

Cell body of Purkinje cell

Purkinje cell axons projectinto the white matter of

the cerebellum. Purkinje cells LM x 400



• Components (sagittal section)• Cerebellar cortex• Arbor vitae “tree of life”

• Branching pattern of inner cerebellar white matter

• Cerebellar peduncles• Link cerebellum to brain stem• Three on each side

1. Superior2. Middle3. Inferior


Figure 13.4 3

A sagittal section through the vermis showing the internal organization ofthe cerebellum and the locations of the three cerebellar peduncles

Midbrain

Anterior lobe

Arbor vitae

Cerebellar nucleusCerebellar cortexPosterior lobe

Choroid plexus ofthe fourth ventricle

Medulla oblongata

PonsCerebellar Peduncles

Superior cerebellar peduncleMiddle cerebellar peduncleInferior cerebellar peduncle

Spinal cordLateral view


Figure 13.4 3


Module 13.4 Review

a. Identify the components of the cerebellar gray matter.

b. Describe the arbor vitae, including its makeup, location, and function.

c. Describe ataxia.


Module 13.5: Midbrain

• Midbrain• Most complex and integrative portion of brain

stem

• Can direct complex motor patterns at subconscious level

• Influences activity level of entire nervous system



• Midbrain components• Corpora quadrigemina

• Superior colliculus (colliculus, hill)• Receives visual inputs from thalamus

• Controls reflex movements of eyes, head, and neck in response to visual inputs

• Inferior colliculus• Receives auditory data from nuclei in medulla

oblongata and pons

• Controls reflex movements of head, neck, and trunk in response to auditory inputs



• Midbrain components (continued)• Reticular activating system (RAS)

• Specialized part of reticular formation• Stimulation to RAS makes you more alert/attentive

• Damage to RAS causes unconsciousness

• Red nucleus• Receives information from cerebrum and cerebellum• Issues commands that affect upper limb position and

background muscle tone

• Substantia nigra (nigra, black)• Dark cells that adjust basal nuclei activity in cerebrum


Figure 13.5 1

A posterior view of the midbrain showing the majorsuperficial landmarks and the underlying nuclei

Corpora Quadrigemina

Superior colliculus

Inferior colliculus

Thalamus

Pineal gland

Red nucleus

Substantia nigra

Cerebral peduncles

Reticular activating system (RAS)

Posterior view ofbrain stem anddiencephalon


Figure 13.5 3

Two views of the brain stem showing the anatomy of the midbrain in relation to the brain stem as a whole

Cranial Nervesof Brain Stem

Midbrain

Cerebellar Peduncles

Posterior viewLateral view

Spinal cord

Medulla oblongata Medulla oblongata

Spinal cord

Choroid plexusin roof of fourthventricle

Dorsal rootsof spinal nervesC1 and C2

IVIVIII

V

VIVII

VIIIIXX

XIXII

Spinalnerve C1

Spinalnerve C2

Cerebral peduncle

Superior colliculus

Inferior colliculus

Superior cerebellar peduncle

Middle cerebellar peduncle

Inferior cerebellar peduncle

Pons

Ventral root Dorsal root



• Midbrain components (continued)• Tectum

• Roof of midbrain

• Region posterior to aqueduct of midbrain

• Tegmentum• Area anterior to aqueduct of midbrain


Figure 13.5 2

A superior view of a horizontal section through the midbrainPosterior

Anterior

Tectum

Aqueduct ofthe midbrainTegmentum

Superior colliculus

Red nucleus

Substantia nigra

Cerebral peduncle


Figure 13.5 3


Module 13.5 Review

a. Cranial nerves III to XII arise from which structure?

b. Identify the sensory nuclei contained within the corpora quadrigemina.

c. Which area(s) of the midbrain control reflexive movements of the eyes, head, and neck?


Module 13.6: Diencephalon

• Diencephalon components• Epithalamus• Thalamus• Hypothalamus



• Epithalamus• Roof of diencephalon, superior to third

ventricle

• Anterior portion• Marked by:

• Anterior commissure (tract interconnecting cerebral hemispheres)

• Optic chiasm (where optic nerves connect to brain)

• Contains extensive area of choroid plexus that extends into interventricular foramina



• Epithalamus (continued)• Posterior portion

• Pineal gland• Secretes melatonin (hormone regulating day-night

cycles and some reproductive functions)



• Thalamus• On each side of brain, superior to midbrain

• Final point for ascending sensory information to be relayed or projected to cerebral cortex• Acts as a filter, only passing on small portion of

sensory information

• Has regions that contain nuclei or groups of nuclei that connect to specific regions of cerebral cortex


Figure 13.6 3

The regions of the thalamus, each of which containsnuclei or groups of nuclei that connect to specificregions of the cerebral cortex

Medial group

Posteriorgroup

Lateral group

Anteriorgroup

V e n t r a lg r o u p

Left thalamus

Pulvinar

Medial geniculatenucleus

Lateral geniculatenucleus

Note: colors indicatethe associated areasof the cerebral cortex



• Thalamus (continued)• Components

• Interthalamic adhesion • Connects thalamic hemispheres, but no neural

fibers cross

• Lateral geniculate (genicula, little knee) nucleus• Receives visual information over optic tract

and relays signals to midbrain and occipital lobe

• Medial geniculate nucleus• Relays auditory information from inner ear

receptors to appropriate cerebral cortex area


Figure 13.6 2

The thalamus and important landmarksmade visible by the removal of thecerebral hemispheres and cerebralpeduncles

Lateral geniculate nucleus

Medial geniculate nucleusOptic chiasm

Optic tract

Cerebral peduncle(midbrain) Lateral view of the

left thalamus and midbrain

Thalamus


Figure 13.6 4



• Hypothalamus• Contains important control and integrative

centers• Centers may be stimulated by:

1. Sensory information from cerebrum, brain stem, and spinal cord

2. Changes in CSF and interstitial fluid composition

3. Chemical stimuli from blood because this area lacks blood–brain barrier



• Hypothalamus (continued)• Components

• Infundibulum• Connects to pituitary gland

• Mamillary bodies• Control feeding reflexes like licking and swallowing

• Hormonal centers• Secrete chemical messengers that control endocrine

cells in anterior pituitary

• Secrete two hormones released by posterior pituitary



• Hypothalamus (continued)• Components

• Nuclei (autonomic centers that control cardiovascular and vasomotor centers of medulla oblongata)• Preoptic area

• Regulates body temperature through adjustments in blood flow and sweat gland activity

• Suprachiasmatic nucleus• Coordinates day-night cycles of activity/inactivity


Figure 13.6 4

Infundibulum

Anteriorpituitary

gland

Posteriorpituitary

gland

Mamillary body

Pons

Hypothalamus

ThalamusAutonomic centers

Preoptic area

Suprachiasmatic nucleus

Hormonal centers

Hypothalamic Nuclei

A sagittal section of the brain showing thestructure of the hypothalamus


Module 13.6 Review

a. Name the main components of the diencephalon.

b. Damage to the lateral geniculate nuclei of the thalami would interfere with what particular function?

c. Which component of the diencephalon is stimulated by changes in body temperature?


Module 13.7: Limbic system

• The limbic system• Includes nuclei and tracts along border of

cerebrum and diencephalon

• Is a functional grouping rather than anatomical• Through experimental stimulation, many

functional areas/centers identified • Emotional areas for rage, fear, pain, sexual arousal, and

pleasure

• Areas that produce heightened alertness/generalized excitement, generalized lethargy, and sleep



• Also known as motivational system

• Functions

1. Establishing emotional states

2. Linking conscious, intellectual functions of cerebral cortex with unconscious and autonomic functions of brain stem

3. Facilitating memory storage and retrieval



• Cerebral components (also called limbic lobe)• Cingulate gyrus (superior portion)

• Parahippocampal gyrus (inferior portion)

• Hippocampus• Diencephalon components

• Anterior group of thalamic nuclei

• Hypothalamus

• Mamillary bodies


Figure 13.7 1

A diagrammatic sagittal section showing the position andorientation of the major components of the limbic system

Components of theLimbic System in theCerebrum

Components of theLimbic System in theDiencephalon

Corpuscallosum Fornix

Centralsulcus

Pinealgland

Temporallobe of

cerebrum

Anterior group ofthalamic nuclei

Hypothalamus

Mamillary body

Limbic lobe(shown in green)

Cingulate gyrus(superior portion oflimbic lobe)Parahippocampal gyrus(inferior portion of limbiclobe)Hippocampus



• Specific functional areas• Anterior group of thalamic nuclei

• Relay information from mamillary body to cingulate gyrus on same side

• Hippocampus• Shaped like a sea horse (hippocampus)

• Important in learning, especially in storage and retrieval of long-term memories



• Specific functional areas (continued)• Fornix (arch)

• White matter tract connecting hippocampus with hypothalamus

• Amygdaloid (amygdale, almond) body• Interface between limbic system and cerebrum

and various sensory systems

• Plays a role in regulation of heart rate, control of “fight or flight” response, and linking emotions to specific memories


Figure 13.7 2

Hippocampus

Parahippocampalgyrus

Cingulategyrus

Corpuscallosum

Mamillary body

Amygdaloid body

Olfactory tract

Hypothalamic nuclei

Anterior group of thalamic nucleiFornix

A sectional view of important limbic system components and nuclei


Module 13.7 Review

a. List the primary functions of the limbic system.

b. Which region of the limbic system is particularly important for the storage and retrieval of long-term memories?

c. Damage to the amygdaloid body would interfere with the regulation of which division of the autonomic nervous system?


Module 13.8: Basal nuclei of cerebrum

• Basal nuclei of cerebrum• Also known as basal ganglia

• Are masses of gray matter within each hemisphere deep to lateral ventricle floor

• Provide subconscious control of skeletal muscle tone and help coordinate learned movement patterns

• Normally do not initiate movement, but provide general pattern and rhythm


Module 13.8: Basal nuclei of cerebrum

• Basal nuclei of cerebrum components• Caudate nucleus• Lentiform (lens-shaped) nucleus

• Medial globus pallidus (pale globe)• Lateral putamen

• Axon bundles connecting cerebral cortex to diencephalon and brain stem pass around and between basal nuclei• = Internal capsule


Figure 13.8 1

Lateral view

Thalamus

Tail of caudatenucleus

Lentiformnucleus

Amygdaloidbody

Head ofcaudatenucleus

A lateral view of the brain showing the locations of thecaudate and lentiform nuclei, which constitute thebasal nuclei


Figure 13.8 1

A dissected horizontal section showing thelocations of the caudate nuclei

Caudate nucleus

Pineal gland

Lateral ventricle

Third ventricle

Choroid plexus

Thalamus

Putamen

Internal capsule

Horizontal section, dissected

Thalamus


Lentiformnucleus

Amygdaloidbody


Lateral view

Fornix


Figure 13.8 1

Lateral ventricleCorpus callosum

Septum pellucidum

Internal capsule

Claustrum

Lateral sulcus

Anteriorcommissure

Tip of lateralventricle

Frontal sectionAmygdaloid body

Globuspallidus

Putamen

Caudate nucleus

Lentiformnucleus

Lateral view

Thalamus


Lentiformnucleus


Basal Nuclei

A frontal section of the brain showing the locations of the basal nuclei

Amygdaloidbody


Module 13.8 Review

a. Define the basal nuclei.

b. Describe the caudate nucleus.

c. What clinical signs would you expect to observe in an individual who has damage to the basal nuclei?


Module 13.9: Cerebral superficial landmarks

• Cerebral superficial landmarks• Help to divide each cerebral hemisphere into lobes• Central sulcus

• Deep groove dividing anterior frontal lobe from more posterior parietal lobe

• Precentral gyrus• Anterior to central sulcus• Contains primary motor cortex

• Postcentral gyrus• Posterior to central sulcus• Contains primary sensory cortex

• Receives sensory information from body



• Parieto-occipital sulcus• Separates parietal and occipital lobes

• Lateral sulcus• Separates frontal and temporal lobes

• Insula (island)• An “island” of cortex

• Medial to lateral sulcus


Figure 13.9 1

A lateral view of the brain showing the lobes of the cerebral cortex in the left cerebral hemisphere

The lobes of the cerebral cortex in the leftcerebral hemisphere, shownin lateral view

Central sulcusPostcentral gyrus

Parietal lobe

Occipital lobe

Temporal lobe

Cerebellum

Medulla oblongata

Pons

Lateral sulcus

Frontal lobe

Precentral gyrus


Figure 13.9 2

Retraction of the superficial cerebral cortex alongthe lateral sulcus to expose the insula

Insula

A lateral view of the brain showing the lobes of the cerebral cortex in the left cerebral hemisphere


Figure 13.9 2


Figure 13.9 3

Cerebellum

Fourth ventricle

Aqueduct of the midbrain

Corpora quadrigemina

Pineal gland

Occipital lobe

Parieto-occipital sulcus

Parietal lobe

Limbic lobe

Postcentral gyrusCentral sulcusPrecentral gyrus

Frontal lobe

Corpus callosum

Temporal lobePons

Medulla oblongata

Mamillary body

Optic chiasm

Hypothalamus

Thalamus

A midsagittal view showing the inner boundaries of the lobes of the cerebral cortex(Structures outside of the cerebrum are labeled in italics.)


Figure 13.9 3



• General facts about cerebral hemispheres to remember• Each hemisphere receives sensory information from and

sends motor information to the opposite side of body• Has no known functional significance

• Hemispheres may look identical but may have different functions

• Mapping of specific functions to specific areas is imprecise• Boundaries are indistinct and areas may overlap

• Some functions (like consciousness) may be found in multiple regions


Module 13.9 Review

a. Identify the lobes of the cerebrum and indicate the basis for their names.

b. Describe the insula.

c. What effect would damage to the left postcentral gyrus produce?


Module 13.10: Specialized functional regions in cerebral hemispheres

• Specialized functional regions in cerebral hemispheres• Motor cortex

• Neurons here are called pyramidal cells because of their shape

• Somatic motor association area• Responsible for coordination of learned movements



• Sensory areas• Sensory cortex

• Receives somatic sensory information from receptors for touch, pressure, pain, vibration, taste, or temperature

• Somatic sensory association area• Monitors activity in primary sensory cortex

• Gustatory cortex• Area within insula that receives taste receptor information

• Olfactory cortex• Receives olfactory receptor information



• Sensory areas (continued)• Auditory cortex

• Primary auditory cortex• Monitors auditory (sound) information

• Auditory association area• Monitors sensory activity in auditory cortex and

recognizes sounds, such as spoken words



• Sensory areas (continued)• Visual cortex

• Primary visual cortex• Receives information from lateral geniculate nuclei

• Visual association area• Monitors activity in visual cortex and interprets results

• Example: recognizing “c” “a” “r” together is the word “car”


Figure 13.10 1

The motor and sensory cortexes and the association areas for each

Motor CortexSensory Cortex

Visual Cortex

Auditory Cortex

Central sulcus

Somatic sensoryassociation area

Primary visual cortex

Visual association areaLateral sulcus

TEMPORAL LOBE

PARIETAL LOBE

OCCIPITALLOBEFRONTAL

LOBE

Somatic motorassociation area

Gustatory Cortex

Olfactory Cortex

Primary auditory cortex

Auditory association area



• Integrative centers• Concerned with performance of complex

processes such as speech, writing, mathematics, and spatial relationships

• Restricted to either right or left hemisphere



• Integrative centers (continued)• General interpretive area

• Also known as the Wernicke area

• Receives information from all sensory association areas

• Present only in one hemisphere (typically the left)

• Plays an essential role in personality by integrating sensory information and accessing visual and auditory memories

• Speech center• Also known as the Broca area or motor speech area

• Lies in same hemisphere as general interpretive area

• Regulates patterns of breathing and vocalization needed for normal speech



• Integrative centers (continued)• Frontal eye field

• Controls learned eye movements such as scanning text

• Prefrontal cortex• Coordinates information relayed from association

areas

• Performs abstract intellectual functions such as predicting consequences of events or actions


Figure 13.10 2

Locations of some integrative centers, which are concerned with theperformance of complex processes

Frontal eye field

General interpretive area(Wernicke area)Prefrontal cortex

Speech center (Broca area)



• Hemisphere lateralization (specialized functions of each hemisphere)• Left cerebral hemisphere

• Contains general interpretive and speech centers

• Is responsible for language-based skills such as reading, writing, speaking

• Premotor cortex controlling hand movements is larger for right-handed individuals

• Important in performing analytical tasks such as mathematics and logic



• Hemisphere lateralization (continued)• Right cerebral hemisphere

• Analyzes sensory information and relates body to sensory environment

• Examples: recognize faces, understanding 3-D relationships

• Important in analyzing emotional context of conversation

• Example: “Get lost!” or “Get lost?”



• Hemisphere lateralization (continued)• Left-handedness

• Represents about 9% of population

• Controlled by primary motor cortex of right hemisphere

• In an unusually high percentage of musicians and artists

• Primary motor cortex and association areas on right cerebral hemisphere are near spatial visualization and emotion association areas


Figure 13.10 3

Speech center

Writing

Auditory cortex(right ear)

General interpretive center(language and mathematical

calculation)

Visual cortex(right visual field)

Visual cortex(left visual field)

Spatial visualizationand analysis

Auditory cortex(left ear)

Analysis by touch

Anterior commissure

Prefrontalcortex

Prefrontalcortex

LEFT HAND RIGHT HAND

In most people, the left hemisphere contains the generalinterpretive and speech centers and is responsible forlanguage-based skills. Reading, writing, and speaking, forexample, depend on processing done in the left cerebralhemisphere, in addition, the premotor cortex that functionsin the control of hand movements is larger on the left sidefor right-handed individuals than for left-handedindividuals. The left hemisphere is also important inperforming analytical tasks, suchas mathematics and logic.

The right cerebral hemisphere analyzes sensoryinformation and relates the body to the sensoryenvironment. Interpretive centers in this hemisphere enableyou to identify familiar objects by touch, smell, sight, taste,or feel. For example, the right hemisphere plays a dominantrole in recognizing faces and in understandingthree-dimensional relationships. It is also important inanalyzing the emotional context of a conversation—for instance, distinguishing between the threat “Get lost!” and the question “Get lost?”

Left Cerebral Hemisphere Right Cerebral Hemisphere

A schematic representation of hemispheric lateralization

CORPUSCALLOSUM


Module 13.10 Review

a. Where is the primary motor cortex located?

b. Which senses are affected by damage to the temporal lobes?

c. Which brain part has been affected in a stroke victim who is unable to speak?


Module 13.11: White matter in the brain

• Functional groups of white matter in inner cerebrum• Association fibers

• Interconnect areas of neural cortex within a hemisphere• Shortest fibers connect one gyrus to another

(= arcuate fibers)• Longest fibers are organized into bundles or fasciculi

and connect frontal lobe to other lobes of same hemisphere (= longitudinal fasciculi)


Figure 13.11 1

Arcuate fibers

Longitudinal fasciculi

Lateral view

The locations of association fibers,which interconnect areas ofneural cortex within asingle cerebral hemisphere



• Functional groups of white matter in inner cerebrum (continued)• Commissural (commissura, crossing over) fibers

• Interconnect cerebral hemispheres

• Corpus callosum• Most substantial and important of commissural fibers

• Contains more than 200 million axons carrying more than 4 billion impulses per second

• Anterior commissure• Importance increases if corpus callosum is damaged



• Functional groups of white matter in inner cerebrum (continued)• Projection fibers

• Link cerebral cortex to other CNS areas

• Includes both sensory (ascending) and motor (descending) fibers

• All must pass through diencephalon

• Entire mass known as the internal capsule


Figure 13.11 2

Anterior commissure

Corpus callosum

LongitudinalfissureProjection fibers of

internal capsule

Anterior view

The locations of important commissural fibers, which interconnect the cerebralhemispheres, and projection fibers, which link the cerebral cortex to the restof the brain


Module 13.11 Review

a. What special names are given to axons in the white matter of the cerebral hemispheres?

b. What is the function of the longitudinal fasciculi?

c. What are fibers carrying information between the brain and spinal cord called, and through which brain regions do they pass?


CLINICAL MODULE 13.12: Brain activity and electroencephalograms

• Neural function depends on electrical impulses

• Electrical activity changes as certain areas are stimulated or quieted down

• Electrical activity at any time generates an electrical field that can be measured using electrodes on the scalp

• A printout of that activity = electroencephalogram (EEG)

• Electrical patterns observed = brain waves


Figure 13.12 1

The four types of brain waves as they appear on an electroencephalogram (EEG)



• Brain waves• Alpha waves

• Occur in brains of healthy awake adults that are resting with eyes closed

• Vanish when sleeping or concentrating on a specific task

• Beta waves• Higher-frequency waves

• Typical of people concentrating on a task or in a state of psychological tension



• Brain waves (continued)• Theta waves

• May appear transiently during sleep in normal adults

• Most often observed in children and in intensely frustrated adults

• In certain circumstances, may indicate presence of brain disorder such as a tumor

• Delta waves• Very large amplitude, low frequency waves

• Normally seen during sleep in all ages

• Also seen in infants and awake adults with brain damage from a tumor, vascular blockage, or inflammation


Figure 13.12 1

The four types of brain waves as they appear on an electroencephalogram (EEG)

Alpha waves

Beta waves

Theta waves

Delta waves



• Abnormal brain activity• Electrical activity in each hemisphere is generally

synchronized by thalamus

• Asynchrony may indicate localized damage or cerebral abnormalities

• Seizures• Temporary cerebral activity disorder accompanied by

• Abnormal movements

• Unusual sensations

• Inappropriate behaviors

• Some combination of above symptoms

• Can start in one area and spread across cortical surface



• Abnormal brain activity (continued)• Epilepsies

• Clinical conditions characterized by seizures

• Also known as seizure disorders


CLINICAL MODULE 13.12 Review

a. Define electroencephalogram (EEG).

b. Describe the four wave types associated with an EEG.

c. Differentiate between a seizure and epilepsy.


Module 13.13: Cranial nerves

• Cranial nerves • Can be classified as:

• Sensory

• Special sensory

• Motor

• Mixed

• Innervate head, neck, and some torso regions


Figure 13.13

The branches of the 12 cranial nerves, their functions (motor, sensory, or mixed), and the structures they innervate

Optic nerve (II)

Abducens nerve (VI)

Oculomotor nerve (III)Trochlear nerve (IV)Olfactory nerve (I)

Olfactory tract

Olfactory bulb

Pituitary gland

Semilunarganglion (V)Pons

Geniculateganglion (VII)

Medullaoblongata

To tonguemuscles

To sternocleidomastoidand trapezius muscles

Inferior ganglion (X)Superior ganglion (X)Inferior ganglion (IX)

Superior ganglion (IX)

Vestibulocochlear nerve (VIII)

Sensory nerve toposterior tongue

Motor nerve topharyngeal muscles

Sensory nerve totongue and soft palate

Motor nerve to facial muscles

Motor nerve to muscles ofmastication

Ophthalmic branchMaxillary branch

Mandibular branch

Trigeminal nerve (V)

Facial nerve (VII)

Cochlear branch

Vestibular branch

Glossopharyngealnerve (IX)

Vagusnerve (X)

Hypoglossalnerve (XII)

Accessorynerve (XI)

KEYSensory nervesMotor nerves


Figure 13.13


Module 13.13 Review

a. Identify the cranial nerves by name and number.

b. Which cranial nerves have motor functions only?

c. Which cranial nerves are mixed nerves?


Section 2: Sensory and Motor Pathways

• Learning Outcomes• 13.14 Explain the ways in which receptors can

be classified.• 13.15 List the types of tactile receptors, and

specify the functions of each.• 13.16 Identify and describe the major sensory

pathways.• 13.17 Describe the components, processes,

and functions of the somatic motor pathways.



• Learning Outcomes• 13.18 Describe the levels of information

processing involved in motor control.

• 13.19 CLINICAL MODULE Describe the roles of the nervous system in referred

pain, Parkinson disease, rabies, cerebral palsy, amyotrophic lateral

sclerosis, Alzheimer disease, and multiple sclerosis.



• General senses• Our sensitivity to temperature, pain, touch,

pressure, vibration, and proprioception• Receptors that respond to these stimuli are found

throughout the body• Are relatively simple in structure• Size of the area each receptor monitors

(= receptive field) varies• Can be as large as 7 cm (2.5 in.) as on general body

surfaces or as small as 1 mm as on tongue or fingertips• Size of receptive field is inversely related to ability to

accurately describe location of stimulus


Figure 13 Section 2 1

Receptive fields, the areas monitored by a single receptor cell

Receptivefield 1

Receptivefield 2



• General senses (continued)• Sensory pathways begin at peripheral

receptors and often end at diencephalon and/or cerebral hemispheres

• Much sensory information does not reach primary sensory cortex and our awareness

• Sensation• Information carried by sensory pathway

• Perception• Conscious awareness of sensation



• Basic events occurring along sensory and motor pathways

• Sensory pathway• Depolarization of receptor

• Stimulus produces graded change in transmembrane potential of receptor (= transduction)

• Action potential generation• If depolarized to threshold, initial segment develops action

potentials

• Greater degree of sustained depolarization = higher frequency of action potentials



• Basic events occurring along sensory and motor pathways (continued)

• Sensory pathway (continued)• Propagation over labeled line

• = Information about one type of stimulus (touch, pressure, temperature) carried on axons

• Brain processes sensory information based on what type of axons are transmitting information

• CNS processing• Occurs at every synapse along labeled line

• May occur at multiple nuclei and centers in CNS



• Basic events occurring along sensory and motor pathways (continued)

• Motor Pathways (one of two responses)1. Immediate involuntary response

• Processing centers in spinal cord or brain stem respond before sensations reach cerebral cortex

2. Voluntary• Perception (only ~1% of sensations)

• Voluntary response • Can moderate, enhance, or supplement simple

reflexive response


Module 13.14: Receptor classification by function and sensitivity

• Free nerve endings• Can be stimulated by many different stimuli

• Examples: chemical, pressure, temperature changes, trauma

• Sensitivity and specificity may be altered by location and presences of accessory structures

• Are simplest receptors, being the dendrites of sensory neurons

• Have branching tips that are unprotected


Figure 13.14 1

Free nerve endings, the branching tips of the dendrites of sensory neurons

Freenerveendings


Module 13.14: General sense receptor classification by function and sensitivity

• Functional classes• Nociceptors

• Pain receptors• Free nerve endings with large receptive fields and

broad sensitivity• Two axon types carry pain information

1. Type A fibers (fast pain)• Such as from injection or deep cut• Quickly reach CNS and trigger fast reflexive responses• Relayed to primary sensory cortex for conscious

attention• Stimulus can be located to an area within a few cm



• Functional classes (continued)• Nociceptors (continued)

• Two axon types carry pain information (continued) 2. Type C fibers (slow pain)

• Such as burning or aching

• Cause generalized activation of thalamus and reticular formation

• Individual aware of pain but only general location



• Functional classes (continued)• Thermoreceptors

• Temperature receptors• Free nerve endings in dermis, skeletal muscles,

liver, and hypothalamus • 3–4× more cold receptors than warm receptors

• No structural differences

• Chemoreceptors• Respond to water-soluble and lipid-soluble

substances dissolved in body fluids (interstitial fluid, plasma, CSF)



• Functional classes (continued)• Mechanoreceptors

• Sensitive to stimuli that distort plasma membrane• Contain mechanically gated ion channels that open

or close in response to:

• Stretching

• Compression

• Twisting

• Other distortions of membrane



• Functional classes (continued)• Mechanoreceptors (continued)

• Three main types1. Proprioceptors

• Monitor position of joints and muscles

• Most complex of general sensory receptors

• Example: muscle spindle

2. Baroreceptors (baro, pressure)

• Detect pressure changes in blood vessels and portions of digestive, reproductive, and urinary tracts



• Functional classes (continued)• Mechanoreceptors (continued)

• Three main types (continued)3. Tactile receptors

• Provide sensations of touch (shape or texture), pressure (degree and frequency of distortion), and vibration

• Fine touch and vibration receptors give detailed information

• Crude touch and pressure receptors provide poor localization and give little information


Figure 13.14 2

A Functional Classification of General Sensory Receptors

Nociceptors Thermoreceptors Chemoreceptors Mechanoreceptors

Painreceptors

Temperaturereceptors

Respond towater-solubleand lipid-solublesubstancesdissolved in bodyfluids

Sensitive tostimuli thatdistort theirplasmamembranes

Myelinated Type A fibers(carry sensations offast pain)

Unmyelinated Type C fibers (carry sensations of slowpain)

Proprioceptors(monitor thepositions of jointsand muscles)

Baroreceptors(detect pressurechanges)

Tactile receptors (provide thesensations of touch, pressure,and vibration)



• Receptor classes based on stimulation response• Tonic receptors

• Always active• Frequency of action potentials generated reflects

background stimulation level• As stimulation changes, AP frequency changes

accordingly

• Phasic receptors• Normally inactive• Become active transiently in response to changing

conditions


Figure 13.14 3

TimeTime

Classification of receptors based on the nature of their response to stimulation

Increased IncreasedNormal Normal Normal NormalStimulus Stimulus

Frequencyof action

potentials

Frequencyof action

potentials

Tonic receptors are always active and generate actionpotentials at a frequency that reflects the background levelof stimulation. When the stimulus increases or decreases,the rate of action potential generation changes accordingly.

Phasic receptors are normally inactive, butbecome active for a short time in response to achange in the conditions they are monitoring.



• Adaptation• Reduction in sensitivity in the presence of a

constant stimulus

• Two types

1. Peripheral adaptation• Occurs at receptor

• Receptor activity decreases with time

2. Central adaptation• Occurs along CNS sensory pathways

• Generally involves inhibition nuclei along pathway


Figure 13.14 4

Site of peripheral adaptation

ReceptorArrivingstimulus

Site of central adaptation

CNS processing centerLabeled line

Adaptation, a reduction in sensitivity in the presence of a constant stimulus


Module 13.14 Review

a. List the four types of general sensory receptors based on function, and identify the type of stimulus that excites each type.

b. Describe the three classes of mechanoreceptors.

c. Explain adaptation, and differentiate between peripheral adaptation and central adaptation.


Module 13.15: Structural receptor classes in skin

• Structural receptor classes in skin• Free nerve endings

• Most common receptors in skin

• Root hair plexus• Monitor distortions and movements of hair follicle• Adapt rapidly

• Tactile discs and Merkel cells• Fine touch and pressure receptors• Are extremely sensitive tonic receptors• Have very small receptive fields• Merkel discs are large epithelial cells in stratum germinativum

closely associated with tactile discs


Figure 13.15

The types of receptors in the skin

Hair

Sensory nerves


Figure 13.15 2

Free Nerve Endings

Are the branching tips of sensoryneurons; are unprotected andnonspecific; can respond to tactile,pain, and temperature stimuli Free nerve

endings

Sensorynerve



• Tactile (Meissner’s) corpuscles• Are sensitive to fine touch, pressure, and low

frequency vibration• Adapt quickly• Fairly large (~100 µm in length and ~50 µm in width)• Most abundant in eyelids, lips, fingertips, nipples,

and external genitalia• Dendrites are highly coiled and interwoven

• Surrounded by modified Schwann cells• Anchored in dermis by fibrous capsule



• Lamellated (lamella, thin plate) corpuscles• Also known as pacinian corpuscles• Sensitive to deep pressure• Fast adapting

• Most sensitive to pulsing or high-frequency vibrating stimuli

• Very large receptors• May reach 4 mm in length and 1 mm in diameter

• Surrounded by layers of collagen fibers separated by interstitial fluid

• Shield dendrite from other stimuli

• Found in dermis of fingers, mammary glands, external genitalia, in fasciae, joint capsules, and viscera



• Ruffini corpuscles• Sensitive to pressure and distortion of reticular

dermis• Are tonic and show little (if any) adaptation• Surrounded by capsule that is continuous with

dermis• Within is a network of dendrites and collagen

fibers


Module 13.15 Review

a. Identify the six types of tactile receptors located in the skin, and describe their sensitivities.

b. Which types of tactile receptors are located only in the dermis?

c. Which is likely to be more sensitive to continuous deep pressure: a lamellated corpuscle or a Ruffini corpuscle?


Module 13.16: Three major somatic sensory pathways

1. Spinothalamic pathway• Neural path

• First-order neuron • From receptor to synapse in spinal cord posterior gray horn

• Second-order neuron• From posterior gray horn, crosses spinal cord and reaches

thalamus

• Third-order neuron• From thalamus to primary sensory cortex

• Sensory homunculus (“little man”) maps somatic sensations to discrete areas in cortex



1. Spinothalamic pathway (continued)• Anterior spinothalamic tracts

• Carry crude touch and pressure sensations from body

• Lateral spinothalamic tracts• Carry pain and temperature sensations from

body



2. Posterior column pathway• Carries sensations of highly localized “fine”

touch, pressure, vibration, and proprioception

• Begins at peripheral receptor and ends in primary sensory cortex

• Sensory axons ascend in fasciculus gracilis and cuneatus

• Medial lemniscus (tract) leads to thalamus



3. Spinocerebellar pathway• Carries proprioceptive information about

position of skeletal muscles, joints, and tendons to cerebellum

• Posterior axons do not cross sides of spinal cord• Pass through cerebellar peduncles of same

side

• Anterior axons do cross over to opposite side of spinal cord


Figure 13.16 4

Posterior column pathway

Spinocerebellar pathway

Spinothalamic pathway

A cross section through the spinal cord showing thelocations of the somatic sensory pathways


Module 13.16 Review

a. Define sensory homunculus.

b. Which spinal tracts carry action potentials generated by nociceptors?

c. Which cerebral hemisphere receives impulses conducted by the right fasciculus gracilis of the spinal cord?


Module 13.17: Somatic motor pathways

• Somatic motor pathways• Always involve at least two motor neurons

1. Upper motor neuron• Cell body in a CNS processing center

2. Lower motor neuron• Cell body in a nucleus of brain stem or spinal cord

• Upper motor neuron synapses on lower, which then innervates a single motor unit of skeletal muscle



• Corticospinal pathway• Provides voluntary control over skeletal muscles

• Sometimes called the pyramidal system• Begins at pyramidal cells in primary motor cortex

• Upper axons descend into brain stem and spinal cord• Synapse with lower motor neurons that control muscles



• Corticospinal pathway (continued)• Upper motor neurons begin along specific areas of the

primary motor cortex that map to muscles in specific areas of the body (= motor homunculus)

• Motor homunculus pattern varies with number of motor units innervated and degree of motor control available

• Synapses with lower motor neurons occur in two tracts1. Corticobulbar (bulbar, brain stem) tracts

• Synapses occur in motor nuclei of cranial nerves

• Provide conscious control over skeletal muscles that move eye, jaw, face, and some muscles of neck and pharynx



• Corticospinal pathway (continued)• Synapses with lower motor neurons occur in two

tracts (continued)2. Corticospinal tracts

• Visible along ventral surface of medulla oblongata as pair of thick bands (pyramids)• ~85% of corticospinal axons cross midline to enter

lateral corticospinal tracts• ~15% descend uncrossed as anterior corticospinal

tracts (crossing over occurs through anterior white commissure at specific spinal segment)

• Provide conscious control over skeletal muscles that move various body areas


Figure 13.17 1

The corticospinal pathway, which providesvoluntary control over skeletal muscles

To skeletalmuscles

Motor nucleiof cranial

nerves

Motor nucleiof cranial

nerves

To skeletalmuscles

To skeletalmuscles

KEY

Lateral corticospinal tract

Anterior corticospinal tract

Corticobulbar tract

Medulla oblongata

Spinal cordUpper motorneuron

Lower motorneuron

Pyramid

Midbrain

Cerebralpeduncle

Motorhomunculus



• Two main pathways for subconscious motor commands

1. Lateral pathway• Primarily concerned with muscle tone and precise

movements of distal limb parts

• Red nucleus (primary nucleus of lateral pathway)• Receives information from cerebrum and cerebellum

• Adjusts upper limb position and background muscle tone

• Axons cross to opposite side of brain and descend through rubrospinal (ruber, red) tracts



• Two main pathways for subconscious motor commands (continued)

2. Medial pathway • Primarily concerned with muscle tone and gross motor control

of neck, trunk, and proximal limb muscles

• Upper motor neurons located in three areas1. Superior and inferior colliculi

• Tectospinal tracts pass axons down to direct reflexive movements of head, neck, and upper limbs to visual/auditory stimuli

2. Reticular formation

• Reticulospinal tracts conduct impulses down spinal cord



• Two main pathways for subconscious motor commands (continued)

2. Medial pathway (continued)• Upper motor neurons located in three areas

(continued)3. Vestibular nucleus (of CN VIII)

• Receive information from inner ear about position and movement of head

• Issue motor commands through vestibulospinal tracts to adjust muscle tone in neck, eyes, head, and limbs


Figure 13.17 2

The locations of centers in the cerebrum,diencephalon, and brain stem that may issuesomatic motor commands as a result of processingperformed at a subconscious level

Nuclei of the Medial Pathway

Superior and inferior colliculiReticular formationVestibular nucleus

Motorcortex

Basalnuclei

Red nucleus

Medulla oblongata

Thalamus

Cerebellarnuclei


Figure 13.17 3

A cross section of the spinal cord showing thelocations of the medial and lateral pathways

Anteriorcorticospinal

tract

Tectospinal tract

Vestibulospinal tract

Reticulospinal tract

Medial PathwayInvolved primarily with the control ofmuscle tone and gross movements ofthe neck, trunk, and proximal limbmuscles

Lateralcorticospinal

tract

Lateral PathwayInvolved primarily with the control of muscle tone and the more precise movementsof the distal parts of thelimbs

Rubrospinal tract


Module 13.17 Review

a. Define corticospinal tracts.

b. Describe the role of the corticobulbar tracts.

c. What effect would increased stimulation of the motor neurons of the red nucleus have on muscle tone?


Module 13.18: Levels of somatic motor control

• Levels of somatic motor control• Many brain areas are involved in controlling body

movements

• Generally, the closer the motor center to the cerebral cortex, the more complex the motor activity• Cerebellum is the exception as it is involved at

multiple levels



• Brain areas involved in increasing levels of motor complexity (as indicated by increasing numbers)

1. Brain stem and spinal cord• Simple cranial and spinal reflexes

2. Pons and medulla oblongata• Balance reflexes and more complex respiratory reflexes

3. Hypothalamus• Reflex motor patterns related to eating, drinking, and sexual

activity; also modifies respiratory reflexes

4. Thalamus and midbrain• Reflexes in response to visual and auditory stimuli



• Brain areas involved in increasing levels of motor complexity (continued)

5. Basal nuclei• Modify voluntary and reflexive motor patterns at

subconscious level

6. Cerebral cortex• Plans and initiates voluntary motor activity

7. Cerebellum• Coordinates complex motor patterns through

feedback loops involving cerebral cortex, basal nuclei, and nuclei of medial and lateral pathways


Figure 13.18 1

The brain structures involved in increasing levels of motor complexity (as indicated by the numbers);the cerebellum is involved in coordinating motor activities at multiple levels

Basal Nuclei

Cerebral CortexThalamus andMidbrain

Hypothalamus

Pons and MedullaOblongata

Brain Stem and Spinal Cord

Cerebellum

Controls reflex motorpatterns related toeating, drinking, andsexual activity; modifies respiratoryreflexes

Control balancereflexes and morecomplex respiratoryreflexes

Control simple cranial andspinal reflexes

Control reflexes inresponse to visualand auditory stimuli

Modify voluntary andreflexive motor patterns at thesubconscious level

Plans andinitiates voluntarymotor activity

Coordinates complexmotor patternsthrough feedbackloops involving thecerebral cortex andbasal nuclei as well asnuclei of the medialand lateral pathways



• Preparing for movement• Once a decision to move has been made,

information is relayed• Frontal lobes motor association areas

basal nuclei & cerebellum


Figure 13.18 2

The path of information flow whenan individual makes a conscious decisionto perform a specific movement

Decision infrontal lobes Basal

nuclei

Motorassociation

areas

Cerebellum

Cerebralcortex



• Performing a movement• As movement begins, responses are relayed from motor

association areas• Motor association areas primary motor cortex medial

and lateral pathways

• Basal nuclei adjust movement patterns in two ways1. Alter pyramidal cell sensitivity, adjusting corticospinal output

2. Change excitatory or inhibitory output of medial and lateral pathways

• Cerebellum monitors somatic sensory input and adjusts motor output as necessary


Figure 13.18 3

The flow of information as an individualbegins a movement

Basalnuclei

Motorassociation

areas

Primarymotorcortex

Other nuclei ofthe medial and

lateral pathwaysCerebellum

Cerebralcortex

Lowermotor

neurons

Corticospinalpathway

Motor activity

The basal nuclei adjust patternsof movement in two ways:1. They alter the sensitivity of the pyramidal cells to adjust the output along the corticospinal tract.2. They change the excitatory or inhibitory output of the medial and lateral pathways.

As the movement proceeds,the cerebellum monitorsproprioceptive and vestibularinformation and comparesthe arriving sensations withthose experienced during previous movements. It thenadjusts the activities of theupper motor neuronsinvolved.



• Effects of primary motor cortex damage• Individual loses ability to exert fine control of

skeletal muscles

• Some voluntary movements can still be controlled by basal nuclei

• Cerebellum cannot fine-tune movements because corticospinal pathway is inoperative

• An individual can stand, balance, and walk

• All movements are hesitant, awkward, and poorly controlled


Module 13.18 Review

a. The basic motor patterns related to eating and drinking are controlled by what region of the brain?

b. Which brain regions control reflexes in response to visual and auditory stimuli that are experienced while viewing a movie?

c. During a tennis match, you decide how and where to hit the ball. Explain how the motor association areas are involved.


CLINICAL MODULE 13.19: Nervous system disorders

• Nervous system disorders• Referred pain

• Sensation of pain in part of body other than actual source• Examples:

• Heart attack pain felt in left arm

• Strong visceral pain causing stimulation of interneurons in specific spinal cord segment of spinothalamic pathway causing pain at body surface


Figure 13.19 1



• Parkinson disease• When substantia nigra neurons are damaged or

secrete less dopamine

• Basal nuclei become more active, increasing muscle tone and producing stiffness and rigidity

• Starting movements is difficult because antagonistic muscle groups do not relax (must be overpowered)

• Movements controlled through intense effort and concentration


Figure 13.19 2

The substantia nigra from individuals with andwithout Parkinson disease

Normal substantia nigra Diminished substantianigra in Parkinson patient



• Rabies• Bite from rabid animal injects rabies virus into

peripheral tissues

• Virus spreads to synaptic knobs and is relayed up axons into CNS through retrograde flow

• Many toxins, pathogenic bacteria, and other viruses also bypass CNS defenses through retrograde flow


Figure 13.19 3

A member of the dog family, common vectorsof the rabies virus


Figure 13.19 3

Rabies viruses

Synaptic knob

Retrograde flow

The movement of rabies viruses in a peripheral axon



• Cerebral palsy (CP)• Refers to a number of disorders that affect

voluntary motor performance• Appears during infancy or childhood and persists

throughout life• Cause may be:

• Trauma associated with premature or stressful childbirth

• Maternal exposure to drugs (including alcohol)• Genetic defect that causes improper motor pathway

development


Figure 13.19 4

An individual with cerebral palsy, a number of disorders thataffect voluntary motorperformance



• ALS (amyotrophic lateral sclerosis)• Commonly known as Lou Gehrig disease (famous

Yankees player who died from disorder)• Noted physicist Stephen Hawking also is afflicted

• Progressive, degenerative disorder that affects motor neurons in spinal cord, brain stem, and cerebrum

• Affects both upper and lower neurons• Causes atrophy of associated skeletal muscles

• Thought to be related to a defect in axonal transport


Figure 13.19 5

Lou Gehrig, the most famous person afflicted withamyotrophic lateralsclerosis (ALS), aprogressive,degenerative disorderthat affects motorneurons



• Alzheimer disease (AD)• Progressive disorder characterized by loss of higher-order

cerebral functions• Most common cause of senile dementia• Symptoms may appear at ages 50–60 years but can affect

younger individuals• Estimated 2 million affected in United States

• ~15% of those over 65• ~50% of those over 85• Causes ~100,000 deaths per year

• AD patients have intracellular and extracellular abnormalities in hippocampus


Figure 13.19 6

The appearance of a neuron from an individual with Alzheimerdisease (AD), a progressive disorder characterized by the lossof higher-order cerebral functions

Abnormaldendrites,axons, and

extracellularproteins form

complexesknown asAlzheimerplaques.



• Multiple sclerosis (MS; sklerosis, hardness)• Disease characterized by recurrent incidents of

demyelination in axons within optic nerve, brain, and spinal cord

• Common signs and symptoms include:• Partial vision loss

• Problems with speech, balance, general motor coordination (including urinary and bowel control)

• In ~1/3 of cases, disease is progressive with more functional impairment with each incident

• First attack often in individuals 30–40 years old• 1.5× more common in women


Figure 13.19 7

Demyelinating neuron

Damage to a neuron from an individual with multiple sclerosis (MS), a disease characterized by recurrentincidents of demyelination that affects axons


CLINICAL MODULE 13.19 Review

a. Define referred pain.

b. Describe how rabies is contracted.

c. Describe amyotrophic lateral sclerosis (ALS).

13 the brain and cranial nerves

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