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The brain isthat part of the CNS con-

tained within the cranialcavity (ﬁgure

13.1). Itis the control center for many

of the body’s functions. The brain is

much like a complexcentralcomputer but

with additionalfunctions that no computer

can asyet match. Indeed, one goal in com-

puter technologyis to make computers that can

function more like the human brain. The brain consists

of the brainstem, the cerebellum, the diencephalon, and the crerebrum (table

13.1). The brainstem includesthe medulla oblongata, pons, midbrain, and retic-

ular formation. The structure ofthe brain is described in this chapter. Its func-

tionsare primarily discussed in the next chapter.

Twelve pairsof cranial nerves, which are part of the PNS, arise directly

from the brain. Two pairsarise from the cerebrum, and the remaining 10 pairs

arise form the brainstem.

This chapter describes the brainstem (434), cerebellum (437), dien-

cephalon(439), cere brum (441), meninges and cerebrospinal ﬂuid (444), blood

supply to the brain (448) development of the CNS (449), and the cranial

nerves(449).

Brain and

Cranial

Nerves

Colorized SEM of a neuron network.

CHAPTER

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Brainstem

Objective

■ Describe the parts of the brainstem and listtheir functions.

The medulla oblongata, pons, and midbrain constitute the

brainstem(ﬁgure 13.2). The brainstem connects the spinal cord to

the remainder of the brain and is responsible for many essential

functions.Damage to small brainstem areas often causes death be-

cause many reﬂexes essential for survival are integrated in the

brainstem,whereas relatively large areas of the cerebrum or cere-

bellum may be damaged without being life-threatening.

Medulla Oblongata

The medulla oblongata (ob-long-gahta˘),often called the

medulla, is about 3 cm long, is the most inferior part of the

brainstem, and is continuous inferiorly with the spinal cord.It

contains ascending and descending nerve tracts; cranial nerve

nuclei;other, related nuclei; and part of the reticular formation.

Superﬁcially,the spinal cord blends into the medulla, but inter-

nally several differences exist. Discrete nuclei, clusters of gray

matter composed mostly of neuron cell bodies and having spe-

ciﬁc functions,are found in the medulla oblongata, whereas the

gray matter of the spinal cord extends as a continuous mass in

the center of the cord. In addition,the nerve tracts w ithin the

medulla don’t have the same organization as those ofthe spinal

cord. Several medullary nuclei function as centers for reﬂexes,

such as those involved in the regulation ofheart rate, blood ves-

sel diameter, respiration, swallowing, vomiting, hiccuping,

coughing,and sneezing.

Part3 Integration and ControlSystems434

Two prominent enlargements on the anterior surface ofthe

medulla oblongata are called pyramids because they are broader

near the pons and taper toward the spinal cord (ﬁgure 13.2a).The

pyramids are descending nerve tracts involved in the conscious con-

trol ofskeletal muscles. Near their inferior ends, most of the ﬁbers of

the descending nerve tracts cross to the opposite side,or decussate

(de¯ku˘-sa¯t,de¯-ku˘sa¯t;the Latin word decussatus means to form an X,

as in the Roman numeral X).This decussation accounts, in part, for

the fact that each half of the brain controls the opposite half of the

body.Its role as a conduction pathway is discussed in the description

ofascending and descending nerve tracts (see chapter 14).

Two rounded,oval structures, called olives, protrude from

the anterior surface ofthe medulla oblongata just lateral to the su-

perior margins ofthe py ramids (ﬁgure 13.2aand b). The olives are

nuclei involved in functions such as balance,coordination, and

modulation ofsound from the inner ear (see chapter 15). The nu-

clei ofcranial ner ves V (trigeminal),IX (glossopharyngeal), X (va-

gus),XI (accessory), and XII (hypoglossal) also are located within

the medulla (ﬁgure 13.2c).

Pons

The part ofthe brainstem just superior to the medulla oblongata is

the pons (see ﬁgure 13.2a), which contains ascending and de-

scending nerve tracts and several nuclei. The pontine nuclei, lo-

cated in the anterior portion of the pons, relay information from

the cerebrum to the cerebellum.

The nuclei for cranial nerves V (trigeminal),VI (abducens),

VII (facial), VIII (vestibulocochlear),and IX (glossophar yngeal)

are contained within the posterior pons.Other important pontine

areas include the pontine sleep center and respiratory center,which

Diencephalon

Brainstem

Thalamus

Cerebrum

Corpus

callosum

Cerebellum

Hypothalamus

Midbrain

Pons

Medulla

oblongata

Figure 13.1

Regionsof the Right Half of the Brain

(asseen in a midsagittal section)

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work with the respiratory centers in the medulla to help control

respiratory movements (see chapter 23).

Midbrain

The midbrain, or mesencephalon, is the smallest region of the

brainstem (see ﬁgure 13.2b).It’s just superior to the pons and con-

tains the nuclei of cranial nerves III (oculomotor),IV (trochlear),

and V (trigeminal).

The tectum (tektu˘ m; roof) (ﬁgure 13.3) of the midbrain

consists offour nuclei that form mounds on the dorsal surface, col-

lectively called corpora (ko¯rpo¯r-a˘; bodies) quadrigemina

(kwahdri-jemi-na˘;four twins). Each mound is called a colliculus

(ko-liku¯-lu˘s; hill); the two superior mounds are called superior

colliculi, and the two inferior mounds are called inferior colli-

culi.The inferior colliculi are involved in hearing and are an inte-

gral part ofthe auditory pathways in the CNS. Neurons conducting

Table 13.1 Divisions and Functions of the Brain

Brainstem

Cerebellum

Medulla oblongata

Pons

Midbrain

Reticular formation

Connects the spinal cord to the cerebrum;

several important functions (see below);

location of cranial nerve nuclei.

Pathway for ascending and descending

nerve tracts; center for several important

reflexes (e.g., heart rate, breathing,

swallowing, vomiting)

Contains ascending and descending nerve

tracts; relay between cerebrum and

cerebellum; reflex centers

Contains ascending and descending nerve

tracts; visual reflex center; part of

auditory pathway

Scattered throughout brainstem; controls

cyclic activities such as the sleep-wake

cycle

Control of muscle movement and tone;

regulates extent of intentional

movement; involved in learning

motor skills

Thalamus

Major sensory relay center; influences

mood and movement

Subthalamus

Contains nerve tracts and nuclei

Epithalamus

Contains nuclei responding to olfactory

stimulation and contains pineal

body

Hypothalamus

Major control center for maintaining

homeostasis and regulating

endocrine function

Conscious perception, thought, and

conscious motor activity; can

override most other systems

Basal nuclei

Control of muscle activity and posture

Limbic system

Cerebrum

Autonomic response to smell, emotion,

mood, and other such functions

Diencephalon

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Sensory nuclei (green)

Motor nuclei (purple)

Solitary

nucleus

Oculomotor nucleus (CN III)

Trochlear nucleus (CN IV)

Trigeminal motor nucleus (CN V)

Abducens nucleus (CN VI)

Facial motor nucleus (CN VII)

Superior salivatory and

lacrimal nuclei (CN VII)

Inferior salivatory nucleus (CN IX)

Nucleus ambiguus (CN IX, X, XI)

Dorsal nucleus of

vagus nerve (CN X)

Hypoglossal nucleus (CN XII)

Taste area

(CN VII, IX)

General visceral

sensory area (CN IX,X)

Cochlear and

vestibular nuclei

(CN VIII)

Sensory trigeminal

nuclei (CN V)

Thalamus

Infundibulum

Cerebral

peduncle

Pyramid

Ventral median

sulcus

Pyramidal

decussation

(a) Anterior view

(b) Posterolateral view

Interthalamic adhesion

Diencephalon

Midbrain

Diencephalon

Midbrain

Medulla

oblongata

Pons

Brainstem

Olive

Superior colliculus

Inferior colliculus

Superior cerebellar

peduncle

Median sulcus

Middle cerebellar

peduncle

Inferior cerebellar

peduncle

Nucleus cuneatus

Nucleus gracilis

Olive

Thalamus

Pineal body

Cerebral

peduncle

Pons

Medulla

oblongata

Diencephalon

Brainstem

Figure 13.2

Brainstem and Diencephalon

(a) Anterior view. (b) Posterolateralview. (c) Brainstem nuclei. The sensorynuclei are shown on the left (green). The motor nuclei are shown on the right (purple).

Even though the nuclei are shown on onlyone side, each half of the brainstem hasboth sensory and motor nuclei. The inset shows the location of the diencephalon

(red) and brainstem (blue). (CN cranial nerve.)

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action potentials from the structures of the inner ear (see chapter

15) to the brain synapse in the inferior colliculi.The superior colli-

culi are involved in visual reﬂexes,and they receive input from the

eyes,the inferior colliculi, the skin, and the cerebrum.

ReﬂexMovements of the Eyes and Head

The superior colliculi regulate the reﬂexmovements of the eyes and

head in response to variousstimuli. When a bright object suddenly

appearsin a person’s ﬁeld of vision, a reﬂex turnsthe eyes to focus on it.

When a person hearsa sudden, loud noise, a reﬂex turns the head and

eyestoward it. When a part of the body, such as the shoulder, is

touched, a reﬂexturns the person’s head and eyes toward thatpar tof

the body. In each situation, the pathwayinvolvesthe superior colliculus.

The tegmentum (teg-mentu˘m; ﬂoor) of the midbrain

largely consists of ascending tracts, like the spinal lemniscus and

the medial lemniscus, from the spinal cord to the brain. The

tegmentum also contains the paired red nuclei, which are so

named because in fresh brain specimens,they are pinkish in color

as the result ofan abundant blood supply. The red nuclei aid in the

unconscious regulation and coordination of motor activities.

Cerebral peduncles (pe-du˘ngklz,pe¯du˘ng-klz; the foot of a col-

umn) constitute that portion of the midbrain ventral to the

tegmentum.They consist primarily of descending tracts from the

cerebrum to the brainstem and spinal cord and constitute one of

the major CNS motor pathways. The substantia nigra (nı¯gra˘;

black substance) is a nuclear mass between the tegmentum and

cerebral peduncles,containing cytoplasmic melanin granules that

give it a dark gray or black color (ﬁgure 13.3).The substantia nigra

is interconnected with other basal nuclei of the cerebrum, de-

scribed later in this chapter,and it’s involved in maintaining mus-

cle tone and in coordinating movements.

Reticular Formation

A group of nuclei collectively called the reticular formation

(see table 13.1) is scattered like a cloud throughout the length of

the brainstem. The reticular formation receives axons from a

large number of sources and especially from nerves that inner-

vate the face.

1. What are the major components of the medulla oblongata,

pons, midbrain, and reticularformation? What are the

general functionsof each region?

Cerebellum

Objective

■ Describe the structure and the majorfunctions of the

cerebellum.

The term cerebellum (ser-e-belu˘m; ﬁgure 13.4) means lit-

tle brain.The cerebellum is attached to the brainstem posterior to

the pons.It communicates with other regions of the CNS through

three large nerve tracts: the superior,middle, andinfer ior cere-

bellar peduncles, which connect the cerebellum to the midbrain,

pons, and medulla oblongata, respectively.The cerebellum has a

gray cortex and nuclei,with white medulla in between. The cere-

bellar cortex has ridges called folia. The white matter of the

medulla resembles a branching tree and is called the arbor vitae

(arbo¯r vı¯te; tree of life). The nuclei of the cerebellum are located

in the deep inferior center ofthe white matter.

The cerebellum consists of three parts: a small inferior

part, the flocculonodular (flok u¯-lo¯-nodu¯-la˘r; floccular,

meaning a tuft of wool) lobe; a narrow central vermis (worm-

shaped); and two large lateral hemispheres (see ﬁgure 13.4).

The ﬂocculonodular lobe is the simplest part of the cerebellum

and helps control balance and eye movements.The vermis and

medial portion of the lateral hemispheres are involved in the

control of posture, locomotion, and fine motor coordination,

thereby producing smooth,ﬂowing movements. The major por-

tion ofthe lateral hemispheres is involved, with the cerebral cor-

tex of the frontal lobe, in planning, practicing, and learning

complex movements.

2. What are the major regions of the cerebellum? Describe the

majorfunctions of each.

Superior

colliculus

Cerebral aqueduct

Tectum

Tegmentum

Substantia nigra

Cerebral

peduncle

Spinal

lemniscus

Medial

lemniscus

Red

nucleus

Figure 13.3

CrossSection Through the Midbrain

Insetshows the level of section.

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Lobule

Anterior lobe

Primary

fissure

Folia

Posterior

lobe

Vermis

Lateral

hemisphere

Medulla

oblongata

Pons

Flocculonodular

lobe

Tonsil

Lateral

hemisphere

Folia

lobe

Vermis

Primary

fissure

Lateral

hemisphere

Folia

Posterior

lobe

Cerebellar

notch

Figure 13.4

Cerebellum

(a) Righthalf of the cerebellum as seen in a midsagittalsection. (b) Inferior view of the cerebellum. (c) Superior view of the cerebellum.

(a)

(b)

(c)

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Diencephalon

Objective

■ List the regionsof the diencephalon, and indicate their

majorfunctions.

Thediencephalon (dı¯-en-sefa˘-lon) is the part of the brain

between the brainstem and the cerebrum (see ﬁgures 13.1 and

13.5). Its main components are the thalamus,subthalamus, epi-

thalamus,and hypothalamus.

Thalamus

Thethalamus (thala˘-mu˘ s; ﬁgure 13.5a and b) is by far the largest

part of the diencephalon, constituting about four-ﬁfths of its

weight.It is a cluster of nuclei shaped somewhat like a yo-yo, with

two large,lateral portions connected in the center by a small stalk

called the interthalamic adhesion, or intermediate mass. The

space surrounding the interthalamic adhesion and separating the

two large portions ofthe thalamus is the third ventricle of the brain.

Most sensory input projects to the thalamus,where sensory

neurons synapse with thalamic neurons, which send projections

from the thalamus to the cerebral cortex.Axons carrying auditory

information synapse in the medial geniculate(je-niku¯-la¯t; Latin,

genu, meaning bent like a knee) nucleus of the thalamus, axons

carrying visual information synapse in the lateral geniculate nu-

cleus, and most other sensory impulses synapse in the ventra l

posterior nucleus.

The thalamus also inﬂuences mood and actions associated

with strong emotions like fear or rage. The ventral anterior

and ventral lateral nuclei are involved in motor functions,

Posterior

nucleus

Mammillary

body

Ventromedial

nucleus

Infundibulum

Anterior nucleus

Supraoptic

nucleus

Optic chiasma

Preoptic area

Dorsomedial

nucleus

Paraventricular

nucleus

Pituitary gland

Interthalamic

adhesion

Thalamus

Corpus callosum

Habenular nucleus

Pineal body

Epithalamus

Hypothalamus

Optic chiasma

Pituitary gland

Subthalamus

Cerebellum

Lateral posterior

nucleus

Lateral dorsal

nucleus

Pulvinar

Lateral geniculate

body

Ventral posterior

nucleus

Ventral lateral

nucleus

Ventral anterior nucleus

Anterior nucleus

Interthalamic

adhesion

Medial nucleus

Diencephalon

Thalamus

Hypothalamus

Figure 13.5

Diencephalon

(a) Generaloverview of the right half of the diencephalon asseen in a midsagittal section. (b) Thalamus showing the nuclei. (c) Hypothalamus showing the nuclei

and righthalf of the pituitary.

(a)

(b)

(c)

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communicating between the basal nuclei,cerebellum, and the mo-

tor cortex (these areas are described later in this chapter).The an-

terior andmedial nuclei are connected to the limbic system and to

the prefrontal cortex (described later in this chapter and in chapter

14).The y are involved in mood modiﬁcation.The lateral dorsal

nucleus is connected to other thalamic nuclei and to the cerebral

cortex and is involved in regulating emotions.The lateral poste-

rior nucleusand the pulvinar (pu˘l-vı¯na˘r ;pillow) also have con-

nections to other thalamic nuclei and are involved in sensory

integration.

Subthalamus

The subthalamus is a small area immediately inferior to the thala-

mus (see ﬁgure 13.5a) that contains several ascending and descending

nerve tracts and the subthalamic nuclei.A small portion of the red

nucleus and substantia nigra ofthe midbrain extend into this area.

The subthalamic nuclei are associated with the basal nuclei

and are involved in controlling motor functions.

Epithalamus

Theepithalamus is a small area superior and posterior to the thal-

amus (see ﬁgure 13.5a). It consists of habenular nuclei and the

pineal body.The habenular (ha˘-benu¯-la˘r) nuclei are inﬂuenced

by the sense ofsmell and are involved in emotional and visceral re-

sponses to odors.The pineal (pine¯-a˘l) bodyis shaped somewhat

like a pinecone,from which the name pineal is derived. It appears

to play a role in controlling the onset ofpubert y,but data are in-

conclusive, so active research continues in this ﬁeld.The pineal

body also may inﬂuence the sleep-wake cycle.

Brain Sand in the Pineal

In about75% of adults, the pineal body contains granules ofcalcium

and magnesium saltscalled “brain sand.” These granulescan be seen

on radiographsand are useful as landmarks in determining whether or

notthe pineal body has been displaced bya pathologic enlargement of a

partof the brain, such as a tumor or a hematoma.

Hypothalamus

The hypothalamus is the most inferior portion of the dien-

cephalon (see ﬁgure 13.5aand c) and contains several small nuclei

and nerve tracts. The most conspicuous nuclei,called the mam-

millary bodies, appear as bulges on the ventral surface of the di-

encephalon.They are involved in olfactory reﬂexes and emotional

responses to odors.A funnel-shaped stalk, the infundibulum (in-

fu˘n-dibu¯-lu˘m), extends from the ﬂoor of the hypothalamus and

connects it to the posterior pituitary gland,or neurohypophysis

(nooro¯-hı¯-pofi-sis). The hypothalamus plays an important role

in controlling the endocrine system because it regulates the pitu-

itary gland’s secretion of hormones,w hich inﬂuence functions as

diverse as metabolism,reproduction, responses to stressful stimuli,

and urine production (see chapter 18).

Part3 Integration and ControlSystems440

Sensory neurons that terminate in the hypothalamus pro-

vide input from (1) visceral organs; (2) taste receptors of the

tongue; (3) the limbic system, which is involved in responses to

smell;(4) speciﬁc cutaneous areas, such as the nipples and external

genitalia; and (5) the prefrontal cortex of the cerebrum carrying

information relative to “mood”through the thalamus. Efferent

ﬁbers from the hypothalamus extend into the brainstem and the

spinal cord, where they synapse with neurons of the autonomic

nervous system (see chapter 16).Other ﬁbers extend through the

infundibulum to the posterior portion of the pituitary gland (see

chapter 18); some extend to trigeminal and facial nerve nuclei to

help control the head muscles involved in swallowing;and some

extend to motor neurons ofthe spinal cord to stimulate shivering.

The hypothalamus is very important in a number of func-

tions that are related to mood and emotion (table 13.2).Sensations

like sexual pleasure,feeling relaxed and “good” after a meal, rage,

and fear are related to hypothalamic functions.

3. Name the four main components of the diencephalon.

4. What are the functions of the thalamus and hypothalamus?

Explain whythe hypothalamus is an important link between

the nervoussystem and the endocrine system.

5. List the general functions of the subthalamus. Name the

partsof the epithalamus and give their functions.

Table 13.2

Function Description

Hypothalamic Functions

Autonomic Helps control heart rate, urine release from the

bladder, movement of food through the

digestive tract, and blood vessel diameter

Endocrine Helps regulate pituitary gland secretions and

influences metabolism, ion balance, sexual

development, and sexual functions

Muscle Controls muscles involved in swallowing and

control stimulates shivering in several muscles

Temperature Promotes heat loss when the hypothalamic

regulation temperature increases by increasing sweat

production (anterior hypothalamus) and

promotes heat production when the

hypothalamic temperature decreases by

promoting shivering (posterior hypothalamus)

Regulation of Hunger center promotes eating and satiety

food and center inhibits eating; thirst center promotes

water intake water intake

Emotions Large range of emotional influences over body

functions; directly involved in stress-related

and psychosomatic illnesses and with feelings

of fear and rage

Regulation of Coordinates responses to the

the sleep– sleep–wake cycle with the other areas

wake cycle of the brain (e.g., the reticular activating

system)

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Cerebrum

Objectives

■ Describe the external anatomyand the internal anatomy of

the cerebrum.

■ Describe the structure of the basal nuclei and limbicsystem.

The cerebrum (figure 13.6) is the part of the brain that

most people think of when the term brain is mentioned. It ac-

counts for the largest portion of the total brain weight, which is

about 1200 g in females and 1400 g in males.Brain size is related

to body size;larger br ains are associated with larger bodies,not

with greater intelligence.

Lateral

fissure

Temporal

lobe

Frontal

lobe

Parietal

lobe

Central

sulcus

Occipital

lobe

Cerebellum

Figure 13.6

The Brain

(a) Superior view. (b) Lateralview of the left cerebral hemisphere.

(b)

Parietal

lobe

Occipital

lobe

Longitudinal

fissure

Right

hemisphere

Left

hemisphere

Frontal

lobe

Sulci

Gyri

Central

sulcus

Precentral

gyrus

Postcentral

gyrus

(a)

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The cerebrum is divided into left and right hemispheres by

alongitudinal ﬁssure (ﬁgure 13.6a). The most conspicuous fea-

tures on the surface of each hemisphere are numerous folds

calledgyri (jı¯rı¯;sing., gyrus), which greatly increase the surface

area ofthe cor tex.The intervening grooves between the gyri are

called sulci (su˘lsı¯; sing., sulcus). A central sulcus, which ex-

tends across the lateral surface ofthe cerebrum from superior to

inferior,is located about midway along the length of the brain.

The central sulcus is located between the precentral gyrusante-

riorly, which is the primary motor cortex, and a postcentral

gyrusposteriorly, which is the primary somatic sensory cortex

(see chapter 14).The general pattern of the g yri is similar in all

normal human brains, but some variation exists between indi-

viduals and even between the two hemispheres of the same

cerebrum.

Each cerebral hemisphere is divided into lobes, which are

named for the skull bones overlying each one (ﬁgure 13.6b).The

frontal lobe is important in voluntary motor function, motiva-

tion,aggression, the sense of smell, and mood. The parietal lobe is

the major center for the reception and evaluation ofsensory infor-

mation,except for smell, hearing, and vision. The frontal and pari-

etal lobes are separated by the central sulcus.The occipital lobe

Part3 Integration and ControlSystems442

functions in the reception and integration of visual input and is

not distinctly separate from the other lobes.The temporal lobe re-

ceives and evaluates input for smell and hearing and plays an im-

portant role in memory. Its anterior and inferior portions are

referred to as the “psychic cortex,”and they are associated with

such brain functions as abstract thought and judgment. The tem-

poral lobe is separated from the rest of the cerebrum by a lateral

ﬁssure,and deep within the ﬁssure is the insula (insoo-la˘; island),

often referred to as a ﬁfth lobe.

The gray matter on the outer surface ofthe cerebrum is the

cortex, and clusters of gray matter deep inside the brain are nuclei.

The white matter ofthe brain between the cortex and nuclei is the

cerebral medulla. This term should not be confused with the

medulla oblongata; medulla is a general term meaning the center

of a structure, or marrow.The cerebral medulla consists of nerve

tracts that connect the cerebral cortex to other areas of cortex or

other parts ofthe CNS. These tracts fall into three main categories:

(1)asso ciation ﬁbers, which connect areas of the cerebral cortex

within the same hemisphere;(2) commissural ﬁbers, which con-

nect one cerebral hemisphere to the other; and (3) projection

ﬁbers, which are between the cerebrum and other parts of the

brain and spinal cord (ﬁgure 13.7).

Association fibers

Commissural fibers

Projection fibers

Nuclei

Internal

capsule

Cerebral

medulla

Cortex

Longitudinal

association

fibers

Commissural fibers

(corpus collosum)

Short

association

fibers

Projection fibers

Cerebellum

Cerebrum

Projection

fibers in

the internal

capsule

Brainstem

Figure 13.7

CerebralMedullary Tracts

(a) Coronalsection of the brain showing commissural, association, and projection ﬁbers. (b) Photograph ofthe left cerebral hemisphere from a lateral view with the

cortexand association ﬁbers removed to reveal the projection ﬁbers of the internalcapsule deep within the brain.

(a) (b)

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6. Deﬁne the terms gyri and sulci. What structures do the

longitudinal ﬁssure, central sulcus, and lateral ﬁssure

separate?

7. Deﬁne the terms cerebral cortex and cerebral medulla.

8. Name the ﬁve lobes of the cerebrum, and describe their

locationsand functions.

9. List three categories of nerve tracts in the cerebral medulla.

Basal Nuclei

Thebasal nuclei, or basal ganglia,are a group of functionally re-

lated nuclei located bilaterally in the inferior cerebrum, dien-

cephalon,and midbrain (ﬁgure 13.8). These nuclei are involved in

the control ofmotor functions (see chapter 14). The nuclei in the

cerebrum are collectively called the corpus striatum(ko¯rpu˘s strı¯-

a¯tu˘m; striped body) and include the caudate (kawda¯t;having a

tail) nucleus and lentiform (lenti-fo¯r m; lens-shaped) nucleus.

They are the largest nuclei of the brain and occupy a large part of

the cerebrum. The subthalamic nucleus is located in the dien-

cephalon,and the substantia nigra is located in the midbrain.

10. List the basal nuclei and state their general function.

LimbicSystem

Parts ofthe cerebrum and diencephalon are grouped together un-

der the title limbic(limbik) system (ﬁgure 13.9).The limbic sys-

tem plays a central role in basic survival functions such as memory,

reproduction, and nutrition. It is also involved in emotions and

memory.Limbus means border, and the term limbic refers to deep

Lentiform nucleus

Caudate nucleus

Corpus

striatum

Basal

nuclei

Subthalamic

nucleus

Amygdaloid nucleus

Thalamus

Substantia nigra

(in midbrain)

Corpus callosum

Caudate nucleus

Internal capsule

Lentiform nucleus

Figure 13.8

BasalNuclei (Ganglia) of the Left Hemisphere

(a) A“transparent 3-D” drawing of the basal nuclei inside the left hemisphere. (b) Photograph of a frontalsection of the brain showing the basal nuclei and other

structures.

(b)

(a)

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portions of the cerebrum that form a ring around the dien-

cephalon. Structurally the limbic system consists of (1) certain

cerebral cortical areas,including the cingulate (singu¯-la¯t;to sur-

round)gyrus, located along the inner surface of the longitudinal

ﬁssure just above the corpus callosum,and the hippocampus; (2)

various nuclei, such as anterior nuclei of the thalamus and the

habenular nuclei in the epithalamus;(3) parts of the basal nuclei;

(4) the hypothalamus,especially the mamillary bodies; (5) the ol-

factory cortex;and (6) tracts connecting the various cortical areas

and nuclei,such as the fornix, which connects the hippocampus to

the thalamus and mammillary bodies. The hippocampus is also

connected to the amygdaloid nucleus.

11. List the parts of the limbic system.

Meninges and CerebrospinalFluid

Objectives

■ Describe the membranes and spacessurrounding the

central nervoussystem.

■ Describe the production and circulation of cerebrospinal ﬂuid.

Meninges

Three connective tissue membranes,the meninges (me˘-ninje¯z),

surround and protect the brain and spinal cord (ﬁgure 13.10).The

most superﬁcial and thickest membrane is the dura mater(doora˘

Part3 Integration and ControlSystems444

ma¯ter;tough mother). Three dural folds, the falx cerebri, the ten-

torium cerebelli,and the falx cerebelli, extend into the major brain

ﬁssures.The falx cerebri (falks se-re¯brı¯;sı¯ckle-shaped) is located

between the two cerebral hemispheres in the longitudinal ﬁssure,

thetentorium cerebelli (ten-to¯re¯-u˘m sere˘-belı¯; tent) is between

the cerebrum and cerebellum,and the falx cerebelli lies between

the two cerebellar hemispheres.

The dura mater surrounding the brain is tightly attached to

and continuous with the periosteum ofthe cranial cavity, forming a

single functional layer.The dura mater and dural folds help hold the

brain in place within the skull and keep it from moving around too

freely.The dura mater around the brain separates in several places,

primarily at the bases ofthe three dural folds, to form dural venous

sinuses.The dural venous sinuses collect most of the blood that re-

turns from the brain, as well as cerebrospinal ﬂuid (CSF) from

around the brain (see Cerebrospinal Fluid,p. 446).The sinuses then

empty into the veins that exit the skull (see chapter 21).

The next meningeal membrane is a very thin,w ispy arach-

noid (a˘-raknoyd; spiderlike; i.e., cobwebs) mater.The space be-

tween this membrane and the dura mater is the subdural space

and contains only a very small amount of serous ﬂuid. The third

meningeal layer,the pia (pı¯a˘,pe¯a˘; affectionate) mater is bound

very tightly to the surface of the brain. Between the arachnoid

mater and the pia mater is the subarachnoid space, which con-

tains weblike strands ofthe arachnoid mater and blood vessels and

is ﬁlled with CSF.

Cingulate gyrus

Corpus callosum

Habenular nucleus

Dentate nucleus

Fimbria

Hippocampus

Amygdaloid nucleus

Fornix

Anterior thalamic

nucleus

Anterior commissure

Septal nucleus

Olfactory bulb

Olfactory cortex

Mammillary body

Figure 13.9

LimbicSystem and Associated Structures of the Right Hemisphere asSeen in a Midsagittal Section

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SubduralHematoma

Damage to the venousdural sinuses can cause bleeding into the

subduralspace, resulting in a subdural hematoma, which can cause

pressure on the brain.

Ventricles

The CNS is formed as a hollow tube that may be quite reduced in

some areas ofthe adult CNS and expanded in other areas (see dis-

cussion ofdeveloment, p. 449). The interior of the tube is lined with

a single layer ofepithelial cells called ependymal (ep-endi-ma˘l;see

chapter 11) cells. Each cerebral hemisphere contains a relatively

large cavity,the lateral ventricle (ﬁgure 13.11). The lateral ventri-

cles are separated from each other by thin septa pellucida(septa˘

pe-loosid-a˘,;sing., septum pellucidum; translucent walls), which lie

in the midline just inferior to the corpus callosum and usually are

fused with each other.A smaller midline cavity,the third ventricle,

is located in the center ofthe diencephalon between the two halves

of the thalamus. The two lateral ventricles communicate with the

third ventricle through two interventricular foramina (foramina

of Monro).The lateral ventricles can be thought of as the ﬁrst and

Dural venous sinus

(superior sagittal sinus)

Dural venous sinus

(inferior sagittal sinus)

Periosteum

Dura mater

One functional

layer

Subdural space

(potential space)

Falx cerebri

Arachnoid mater

Subarachnoid space

Pia mater

Cerebrum

Skull

Dural venous sinus

(superior sagittal sinus)

Periosteum

Dura mater

Subdural space

Arachnoid mater

Subarachnoid space

Vessels in

subarachnoid space

Pia mater

(directly attached to brain

surface and not removable)

Cerebrum

One

functional

layer

Figure 13.10

Meninges

(a) Meningealmembranes surrounding the brain. (b) Frontal section of head to show the meninges.

(b)

(a)

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second ventricles in the numbering scheme,but they are not desig-

nated as such. The fourth ventricle is in the inferior part of the

pontine region and the superior region ofthe medulla oblongata at

the base of the cerebellum.The third ventricle communicates with

the fourth ventricle through a narrow canal,the cerebral aqueduct

(aqueduct of Sylvius), which passes through the midbrain. The

fourth ventricle is continuous with the central canal of the spinal

cord,which extends nearly the full length of the cord. The fourth

ventricle is also continuous with the subarachnoid space through

two apertures in its walls and one in the roof.

CerebrospinalFluid

Cerebrospinal(sere˘-bro¯-spı¯-na˘l; se˘-re¯bro¯ -spı¯-na˘l) ﬂuid (CSF)is

a ﬂuid similar to serum with most ofthe proteins removed. It bathes

the brain and the spinal cord and provides a protective cushion

around the CNS. It also provides some nutrients to CNS tissues.

About 80%–90% ofthe CSF is produced by specialized ependymal

cells within the lateral ventricles,w ith the remainder produced by

similar cells in the third and fourth ventricles. These specialized

ependymal cells,their support tissue, and the associated blood ves-

sels together are called choroid(ko¯royd;lacy)plexuses (pleksu˘s-

ez;ﬁgure 13.12). The choroid plexuses are formed by invaginations

of the vascular pia mater into the ventricles,thus producing a vas-

cular connective tissue core covered by ependymal cells.

CSFand Skull Fractures

In skullfractures in which the meninges are torn, CSFmay leak from the

nose ifthe fracture is in the frontal area or from the ear if the fracture is

in the temporalarea. Leakage of CSF indicatesserious mechanical

damage to the head and presentsa risk of meningitis, because bacteria

maypass from the nose or ear through the tear and into the meninges.

Part3 Integration and ControlSystems446

How the choroid plexuses produce CSF is not fully under-

stood.Some portions of the blood plasma simply diffuse across the

plexus membranes,whereas other portions require facilitated dif-

fusion or active transport.

Endothelial cells ofthe blood vessels in the choroid plexuses,

which are joined by tight junctions (see chapter 4), form the

so-called blood-brain barrier, or, more correctly, the blood-

cerebrospinal ﬂuid barrier.Consequently, substances do not pass

between the cells but must pass through the cells.

CSF ﬁlls the ventricles,the subarachnoid space of the brain

and spinal cord, and the central canal of the spinal cord.Ap-

proximately 23 mL of ﬂuid ﬁlls the ventricles,and 117 mL ﬁlls

the subarachnoid space.The route taken by the CSF from its ori-

gin in the choroid plexuses to its return to the circulation is de-

picted in ﬁgure 13.12.The ﬂow rate of CSF from its origin to the

point at which it enters the bloodstream is about 0.4 mL/min.

CSF passes from the lateral ventricles through the interventricu-

lar foramina into the third ventricle and then through the cere-

bral aqueduct into the fourth ventricle.It can exit the interior of

the brain only from the fourth ventricle.One median aper ture

(foramen of Magendie), which opens through the roof of the

fourth ventricle, and two lateral apertures (foramina of

Luschka),which open through the walls, allow the CSF to pass

from the fourth ventricle to the subarachnoid space.Masses of

arachnoid tissue, arachnoid granulations, penetrate into the

dural venous sinus along the superior edge of the falx cerebri

called the superior sagittal sinus. CSF passes into the blood of

the dural venous sinuses through these granulations.The sinuses

are blood-ﬁlled;thus it is within these dural sinuses that the CSF

reenters the bloodstream. From the dural venous sinuses,the

blood ﬂows through the internal jugular veins to veins of the

general circulation.

Posterior horn of

lateral ventricle

Cerebral aqueduct

Fourth ventricle

Central canal

of spinal cord

Anterior horn of

lateral ventricle

Interventricular

foramen

Third ventricle

Inferior horn of

lateral ventricle

Figure 13.11

Ventriclesof the Brain Viewed from the Left

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Chapter 13 Brain and Cranial Nerves 447

1. Cerebrospinal fluid (CSF) is produced by the

choroid plexuses of each of the four ventricles

(

inset

Superior

sagittal sinus

Ependymal

cells

Connective

tissue

CSF enters

the lumen of

the ventricle

Capillary

containing

blood

Villus of

choroid

plexus

Skull

Dura mater

Arachnoid mater

Pia mater

Subarachnoid

space

Cerebrum

Subarachnoid

space

Falx cerebri

(dura mater)

Arachnoid

granulation

Superior

sagittal sinus

(dural venous sinus)

Arachnoid granulation

Choroid plexus of

lateral ventricle

Subarachnoid space

Interventricular foramen

Choroid plexus of

third ventricle

Choroid plexus of

fourth ventricle

Median aperture

Central canal of

spinal cord

Dura mater

Lateral aperture

Cerebral aqueduct

Subarachnoid space

3. CSF flows from the third ventricle through the

cerebral aqueduct to the fourth ventricle.

2. CSF from the lateral ventricles flows through the

interventricular foramina to the third ventricle.

5. CSF flows through the subarachnoid space to the

arachnoid granulations in the superior sagittal sinus,

where it enters the venous circulation (

inset

4. CSF exits the fourth ventricle through the lateral

and median apertures and enters the subarachnoid

space. Some CSF enters the central canal of the

spinal cord.

ProcessFigure 13.12

Flow ofCSF

CSFﬂow through the ventricles and subarachnoid space is shown by white arrows. Those going through the foramina in the walland roof of the fourth ventricle

depictthe CSF entering the subarachnoid space. CSF passes back into the blood through the arachnoid granulations(white and black arrow), which penetrate the

duralsinus. The black arrows show the direction of blood ﬂow in the sinuses.

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Hydrocephalus

Ifthe foramina of the fourth ventricle or the cerebral aqueduct are

blocked, CSFcan accumulate within the ventricles. Thiscondition is

calledinternal hydrocephalus and it results in increased CSF pressure.

The production ofCSF continues, even when the passages that normally

allow itto exit the brain are blocked. Consequently, ﬂuid buildsinside

the brain, causing pressure thatcompresses the nervous tissue and

dilatesthe ventricles. Compression of the nervous tissue usuallyresults

in irreversible brain damage. Ifthe skull bones are not completely

ossiﬁed when the hydrocephalusoccurs, the pressure may also severely

enlarge the head. The cerebralaqueduct maybe blocked at the time of

birth or maybecome blocked later in life because of a tumor growing in

the brainstem.

Internalhydrocephalus can be successfullytreated by placing a

drainage tube (shunt) between the brain ventriclesand abdominal cavity

to eliminate the high internalpressures. There is some riskof infection

being introduced into the brain through these shunts, however, and the

shuntsmust be replaced as the person grows. A subarachnoid

hemorrhage mayblock the return ofCSF to the circulation. If CSF

accumulatesin the subarachnoid space, the condition iscalled external

hydrocephalus.In this condition, pressure is applied to the brain

externally, compressing neuraltissuesand causing brain damage.

12. Describe the three meninges that surround the CNS. What

are the falxcerebri, tentorium cerebelli, and falx cerebelli?

13. Describe and list the contents of the dural sinuses subdural

space, and subarachnoid space.

14. Name the four ventricles of the brain, and describe their

locationsand the connections between them. What are the

septa pellucida?

15. Describe the production and circulation of CSF. Where does

the CSF return to the blood?

Blood Supply to the Brain

Objectives

■ Describe the blood supply to the brain.

■ Describe the blood-brain barrier.

The brain requires a tremendous amount of blood to main-

tain its normal functions.Even though the brain accounts for only

about 2% of the total weight of the body,it receives approximately

15%-20% ofblood pumped by the heart. Interruption of the brain’s

blood supply for only seconds can cause unconsciousness,and inter-

ruption of the blood supply for minutes can cause irreversible brain

damage.This extreme dependence on blood supply results from the

brain’s very high metabolic rate and,as a result,its extreme dependence

on a constant supply ofoxygen and glucose. Brain cells are not capable

ofstoring high-energy molecules for any length of time and depend al-

most exclusively on glucose as their energy source (see chapter 25).

The brain’s blood supply is illustrated in chapter 21 (see ﬁg-

ures 21.8 and 21.9).Blood reaches the brain through the internal

carotid arteries, which ascend to the head along the anterior-

Part3 Integration and ControlSystems448

lateral part of the neck, and the vertebral arteries, which ascend

along the posterior part of the neck, through the transverse

foramina of the cervical vertebrae. The internal carotid arteries

enter the cranial cavity through the carotid canals,and the verte-

bral arteries enter by the foramen magnum.The vertebral arteries

join together to form the basilar artery,which lies on the ventral

surface of the brainstem. The basilar artery and internal carotid

arteries contribute to the cerebral arterial circle(circle of Willis).

Branches from this circle and from the basilar artery supply blood

to the brain.

The cerebral cortex on each side ofthe brain is supplied by

three branches from the cerebral arterial circle: the anterior,

middle, and poster ior cerebral arteries. The middle cerebral

artery supplies most of the lateral surface of each cerebral hemi-

sphere.The anterior cerebral artery supplies the medial portion

of the parietal and frontal lobes. The posterior cerebral artery

supplies the occipital lobe and the medial surface ofthe tempo-

ral lobe.

The arteries to the brain and their larger branches are lo-

cated in the subarachnoid space.Small cortical arterial branches

leave the subarachnoid space and enter the pia mater,where they

branch extensively.Precapillary branches leave the pia mater and

enter the substance of the brain. Most of these branches are

short and remain in the cortex. Fewer,longer branches extend

into the medulla.

The arteries within the substance of the brain quickly divide

into capillaries.The endothelial cells of these capillaries are com-

pletely surrounded by tight junctions,which prevent movement of

most substances between epithelial cells. Movement ofmaterials

through epithelial cells is regulated by those cells.The capillary en-

dothelial cells,under the inﬂuence of the foot processes of astro-

cytes within the brain tissue and the basement membrane in

between, constitute the blood–brain barrier. Lipid-soluble sub-

stances,such as nicotine, ethanol, and heroin, can diffuse through

the blood–brain barrier and enter the brain.Water-soluble mole-

cules such as amino acids and glucose move across the

blood–brain barrier by mediated transport (see chapter 3).

Drugsand the Blood-Brain Barrier

The permeabilitycharacteristics of the blood–brain barrier mustbe

considered when developing drugsdesigned to affect the CNS. For

example, Parkinson’sdisease is caused bya lack of the neurotransmitter

dopamine, which normallyis produced by certain neuronsof the brain.

Thislack results in decreased muscle controland shaking movements.

Administering dopamine isnot helpful because dopamine cannot cross

the blood–brain barrier. Levodopa (

-dopa), a precursor to dopamine, is

administered instead because itcan cross the blood–brain barrier. CNS

neuronsthen convert levodopa to dopamine, which helps reduce the

symptomsof Parkinson’s disease.

16. Describe the blood supply to the brain. List the arteries

supplying each partof the cerebral cortex.

17. Describe the blood-brain barrier.

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Development of the CNS

Objective

■ Describe the formation of the neural tube, and listthe

structuresthat develop from its variousparts.

The CNS develops from a ﬂat plate of tissue, the neural

plate,on the upper surface of the embr yo,as a result of the inﬂu-

ence ofthe underlying rod-shaped notochord (ﬁgure 13.13a). The

lateral sides of the neural plate become elevated as waves, called

neural folds.The crest of each fold is called a neural crest, and the

center ofthe neur al plate becomes the neural groove.The neural

folds move toward each other in the midline,and the crests fuse to

create a neural tube (ﬁgure 13.13b). The cephalic portion of the

neural tube becomes the brain, and the caudal portion becomes

the spinal cord.Neural crest cells separate from the neural crests

and give rise to sensory and autonomic neurons of the peripheral

nervous system.They also give rise to all pigment cells of the body,

as well as facial bones and dentin ofthe teeth.

A series of pouches develops in the anterior part of the neu-

ral tube (ﬁgure 13.14).The pouch walls become the various por-

tions ofthe adult brain (table 13.3), and the pouch cavities become

ﬂuid-ﬁlled ventricles (ventri-klz). The ventricles are continuous

with each other and with the central canalof the spinal cord.The

neural tube develops ﬂexures that cause the brain to be oriented al-

most 90 degrees to the spinal cord.

Three brain regions can be identiﬁed in the early embryo

(see table 13.3 and ﬁgure 13.14a):a forebrain, or prosencephalon

(pros-en-sefa˘-lon); a midbrain, or mesencephalon (mez-en-

sefa˘-lon); and a hindbrain, or rhombencephalon (rom-ben-

sefa˘-lon).During development, the forebrain divides into the te-

lencephalon (tel-en-sefa˘-lon),which becomes the cerebrum, and

the diencephalon (dı¯-en-sefa˘-lon). The midbrain remains as a

single structure, but the hindbrain divides into the meten-

cephalon (meten-sefa˘-lon),which becomes the pons and cere-

bellum, and the myelencephalon (mı¯el-en-sefa˘-lon), which

becomes the medulla oblongata (ﬁgure 13.14band c).

18. Explain how the neural tube forms. Name the ﬁve divisions

of the neural tube and the partsof the brain that each

division becomes.

19. What do the cavities of the neural tube become in the adult

brain?

Cranial Nerves

Objective

■ Describe the distribution and functions of the cranial

nerves.

The 12 cranial nerves by convention are indicated by Roman

numerals (I–XII) from anterior to posterior (ﬁgure 13.15).A given

cranial nerve may have one or more ofthree functions: (1) sensory,

(2) somatic motor,and (3) parasympathetic (table 13.4). Sensory

functions include the special senses like vision and the more general

senses like touch and pain.Somatic (so¯-matik) motor functions re-

fer to the control of skeletal muscles through motor neurons.Pro-

prioception (pro¯-pre¯-o¯-sepshun) informs the brain about the

Neural

fold

Neural tube

Notochord

1. The neural plate is formed from

ectoderm.

Neural groove

Neural fold

Neural plate

Notochord

Neural groove

Crest of the neural fold

Neural fold

Neural

plate

Cut edge of

amnion

Neural

fold

Closed

neural

tube

Somite

Crest of the neural fold

Neural crest cells

Skin

Neural crest cells

4. The neural folds meet at the

midline to form the neural tube.

The neural tube becomes the

brain and spinal cord.

3. Neural crest cells break away

from the crest of the neural folds.

Neural crest cells give rise to a

number of stuctures: sensory and

autonomic neurons in the PNS,

facial pigment cells, facial bones,

and dentin of the teeth.

2. Neural folds form as parallel

ridges along the embryo.

Figure 13.13

Formation ofthe Neural Tube

(a) A21-day-old human embryo. (b) Cross sections through the embryo. The level of each section isindicated by a line in part (a).

(a)

(b)

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Table 13.3

Early Embryo Late Embryo Adult Cavity Function

Prosencephalon Telencephalon Cerebrum Lateral ventricles Higher brain functions

(forebrain)

Diencephalon Diencephalon (thalamus, Third ventricle Relay center, autonomic

subthalamus, nerve control,

epithalamus, endocrine control

hypothalamus)

Mesencephalon Mesencephalon Mesencephalon Cerebral aqueduct Nerve pathways,

(midbrain) (midbrain) reflex centers

Rhombencephalon Metencephalon Pons and cerebellum Fourth ventricle Nerve pathways,

(hindbrain) reflex centers,

muscle coordination,

balance

Myelencephalon Medulla oblongata Central canal Nerve pathways,

reflex centers

Development of the Central Nervous System (see figure 13.14)

Prosencephalon

Optic vesicle (eye)

Mesencephalon

Rhombencephalon

Spinal cord

Optic vesicle

Spinal cord

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon

Diencephalon

Midbrain

(mesencephalon)

Pons

(from

metencephalon)

Cerebrum

(from telencephalon)

Cerebellum

(from metencephalon)

Spinal cord

Medulla

oblongata

(from

myelencephalon)

Brainstem

Figure 13.14

Developmentof the Brain Segments and

Ventricles

(a) Young embryo. (b) Older embryo. (c) Adult.

(a)

(c)

(b)

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Chapter 13 Brain and Cranial Nerves 451

position of various body parts, including joints and muscles. The

cranial nerves innervating skeletal muscles also contain propriocep-

tive sensory ﬁbers,which convey action potentials to the CNS from

those muscles.Because proprioception is the only sensory function

of several otherwise somatic motor cranial nerves, however,that

function is usually ignored, and the nerves are designated by con-

vention as motor only.Parasympatheticfunction involves the regu-

lation of glands, smooth muscles, and cardiac muscle. These

functions are part of the autonomic nervous system and are dis-

cussed in chapter 16. Several of the cranial nerves have associated

ganglia,and these ganglia are of two types: parasympathetic and sen-

sory.Table 13.5 lists speciﬁc information about each cranial nerve.

The olfactory (I) and optic (II) nerves are exclusively sen-

sory and are involved in the special senses ofsmell and vision, re-

spectively.These nerves are discussed in chapter 15.

Theoculomotor nerve (III) innervates four of the six muscles

that move the eyeball and the levator palpebrae superioris muscle,

which raises the superior eyelid.In addition, parasympathetic nerve

ﬁbers in the oculomotor nerve innervate smooth muscles in the eye

and regulate the size ofthe pupil and the shape of the lens of the eye.

The trochlear (tro¯kle¯-ar) nerve (IV) is a somatic motor

nerve that innervates one of the six eye muscles responsible for

moving the eyeball.

Thetrigeminal (trı¯-jemi-na˘l)nerve (V) has somatic motor,

proprioceptive,and cutaneous sensory functions. It supplies motor

innervation to the muscles of mastication, one middle ear muscle,

one palatine muscle,and two throat muscles. In addition to propri-

oception associated with its somatic motor functions,the trigemi-

nal nerve also carries proprioception from the temporomandibular

joint.Damage to the trigeminal nerve may impede chewing.

The trigeminal nerve has the greatest general sensory func-

tion ofall the cr anial nerves and is the only cranial nerve involved

in sensory cutaneous innervation. All other cutaneous innerva-

tion comes from spinal nerves (see ﬁgure 12.15).Trigeminal means

three twins, and the sensory distribution of the trigeminal nerve

inthe face is divided into three regions, each supplied by a branch

of the nerve. The three branches—ophthalmic, maxillary, and

mandibular—arise directly from the trigeminal ganglion, which

serves the same function as the dorsal root ganglia of the spinal

nerves. Only the mandibular branch has motor axons, which

bypass the trigeminal ganglion, much like the ventral root of a

spinal nerve bypasses a dorsal root ganglion.

Olfactory tract

Optic chiasm

Pituitary gland

Mammillary body

Olive of medulla

oblongata

Medulla

oblongata

Olfactory bulb (olfactory

nerves [I] enter bulb)

Pons

Optic nerve (II)

Oculomotor nerve (III)

Trochlear nerve (IV)

Trigeminal nerve (V)

Abducens nerve (VI)

Facial nerve (VII)

Vestibulocochlear

nerve (VIII)

Glossopharyngeal

nerve (IX)

Vagus nerve (X)

Hypoglossal nerve (XII)

Accessory nerve (XI)

Figure 13.15

Inferior Surface ofthe Brain Showing the Origin of the Cranial Nerves

Table 13.4

Nerve Function Cranial Nerve

Functional Organization

of the Cranial Nerves

Sensory I Olfactory

II Optic

VIII Vestibulocochlear

Somatic motor IV Trochlear

VI Abducens

XI Accessory

XII Hypoglossal

Somatic motor V Trigeminal

and sensory

Somatic motor III Oculomotor

and parasympathetic

Somatic motor, VII Facial

sensory, and IX Glossopharyngeal

parasympathetic X Vagus

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In addition to these cutaneous functions, the maxillary and

mandibular branches are important in dentistry.The maxillary nerve

supplies sensory innervation to the maxillary teeth,palate, and gingiva

(jinjı¯-va˘; gum).The mandibular branch supplies sensor y innervation

to the mandibular teeth,tongue, and gingiva. The various nerves in-

Part3 Integration and ControlSystems452

nervating the teeth are referred to as alveolar(al-ve¯o¯-la˘r; refers to the

sockets in which the teeth are located).The superior alveolar nerves

to the maxillary teeth are derived from the maxillary branch of the

trigeminal nerve,and the inferior alveolar nerves to the mandibular

teeth are derived from the mandibular branch ofthe trigeminal nerve.

Table 13.5

Cranial Nerve Foramen or Fissure* Function

I: Olfactory Cribriform plate Sensory

Special sense of smell

II: Optic Optic foramen Sensory

Special sense of vision

III: Oculomotor Superior orbital fissure Motor

†

and parasympathetic

Motor to eye muscles (superior, medial, and inferior rectus; inferior

oblique) and upper eyelid (levator palpebrae superioris)

Proprioceptive from those muscles

Parasympathetic to the sphincter of the pupil (causing constriction)

and the ciliary muscle of the lens (causing accomodation)

Cranial Nerves and Their Functions

*Route of entry or exit from the skull.

†

Proprioception is a sensory function, not a motor function; however, motor nerves to muscles also contain some proprioceptive afferent fibers

from those muscles. Because proprioception is the only sensory information carried by some cranial nerves, these nerves still are considered "motor."

Olfactory

bulb

Cribiform plate

of ethmoid bone

Olfactory tract

(to cerebral cortex)

Fibers of

olfactory

nerves

Eyeball

Mammillary

body

Pituitary

gland

Optic nerve

Optic tract

Optic chiasm

To ciliary

muscles

Oculomotor

nerve

Medial rectus

muscle

Inferior

oblique

muscle

To sphincter

of the pupil

Ciliary

ganglion

Optic

nerve

Inferior

rectus

muscle

Levator palpebrae

superioris muscle

Superior

rectus muscle

continued

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Chapter 13 Brain and Cranial Nerves 453

Table 13.5

Cranial Nerve Foramen or Fissure* Function

IV: Trochlear Superior orbital fissure Motor

†

Motor to one eye muscle (superior oblique)

Proprioceptive from that muscle

V: Trigeminal

The trigeminal nerve is divided into three branches:

the ophthalmic (V

), the maxillary (V

), and the mandibular (V

)

Opththalmic branch (V

) Superior orbital fissure Sensory

Sensory from scalp, forehead, nose, upper eyelid, and cornea

Maxillary branch (V

) Foramen rotundum Sensory

Sensory from palate, upper jaw, upper teeth and gums,

nasopharynx, nasal cavity, skin and mucous membrane of cheek,

lower eyelid, and upper lip

Mandibular branch (V

) Foramen ovale Sensory and motor

†

Sensory from lower jaw, lower teeth and gums, anterior two-thirds

of tongue, mucous membrane of cheek, lower lip, skin of cheek and

chin, auricle, and temporal region

Motor to muscles of mastication (masseter, temporalis,medial and

lateral pterygoids), soft palate (tensor veli palatini), throat (anterior

belly of digastric, mylohyoid), and middle ear (tensor tympani)

Proprioceptive from those muscles

continued

Superior oblique

muscle

Trochlear nerve

Trigeminal nerve

Sensory root

Motor root

Mandibular

branch (V

)

Chorda tympani

(from facial nerve)

To muscles of mastication

Lingual nerve

Opthalmic

branch (V

)

Maxillary

branch (V

)

Trigeminal

ganglion

Inferior alveolar nerve

Submandibular ganglion

To mylohyoid muscle

Superior

alveolar

nerves

To skin

of face

Trigeminal

nerve

Opthalmic

branch (V

)

Mandibular

branch (V

)

Maxillary

branch (V

)

Mental

nerve

continued

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Table 13.5

Cranial Nerve Foramen or Fissure* Function

VI: Abducens Superior orbital fissure Motor

†

Motor to one eye muscle (lateral rectus)

Proprioceptive from that muscle

VII: Facial Internal auditory meatus Sensory, motor,

†

and parasymathetic

Stylomastoid foramen Sense of taste from anterior two-thirds of tongue, sensory from

some of external ear and palate

Motor to muscles of facial expression, throat (posterior belly of

digastric, stylohyoid), and middle ear (stapedius)

Proprioceptive from those muscles

Parasympathetic to submandibular and sublingual salivary glands,

lacrimal gland, and glands of the nasal cavity and palate

continued

Abducens

nerve

Lateral rectus

muscle

To platysma

Pterygopalatine

ganglion

To lacrimal gland and

nasal mucous membrane

To forehead muscles

To orbicularis oculi

To orbicularis oris and

upper lip muscles

Trigeminal

ganglion

Geniculate

ganglion

Facial

nerve

To occipitofrontalis

Chorda tympani

(for salivary glands,

sense of taste)

To digastric and

stylohyoid muscles

To buccinator, lower

lip, and chin muscles

continued

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Chapter 13 Brain and Cranial Nerves 455

Table 13.5

Cranial Nerve Foramen or Fissure* Function

VIII: Vestibulocochlear Internal auditory meatus Sensory

Special senses of hearing and balance

IX: Glossopharyngeal Jugular foramen Sensory, motor,

†

and parasympathetic

Sense of taste from posterior third of tongue, sensory from pharynx,

palatine tonsils, posterior third of tongue, middle ear, carotid sinus

and carotid body

Motor to pharyngeal muscle (stylopharyngeus)

Proprioceptive from that muscle

Parasympathetic to parotid salivary gland and the glands of the

posterior third of tongue

continued

Vestibulocochlear

nerve

Cochlear

nerve

Vestibular nerveVestibular

ganglion

Spiral ganglion

of cochlea

Glossopharyngeal nerve

To parotid gland

Superior and inferior ganglia

To palatine tonsil

To stylopharyngeus muscle

To posterior third

of tongue for

taste and

general sensation

To carotid

body and

carotid sinus

To pharynx

continued

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Table 13.5

Cranial Nerve Foramen or Fissure* Function

X: Vagus Jugular foramen Sensory, motor,

†

and parasympathetic

Sensory from inferior pharynx, larynx, thoracic and abdominal

organs, sense of taste from posterior tongue

Motor to soft palate, pharynx, intrinsic laryngeal muscles (voice

production), and an extrinsic tongue muscle (palatoglossus)

Proprioceptive from those muscles

Parasympathetic to thoracic and abdominal viscera

XI: Accessory Foramen magnum Motor

†

Jugular foramen Motor to soft palate, pharynx, sternocleidomastoid, and trapezius

Proprioceptive from those muscles

continued

Colon

Kidney

Small

intestne

Pancreas

Right vagus

nerve

Left vagus nerve

Pharyngeal

branch

Celiac plexus

Larynx

Right recurrent

laryngeal branch

Spleen

Stomach

Esophageal plexus

Heart

Lung

Cardiac branch

Left recurrent

laryngeal branch

Superior laryngeal

branch

Inferior vagal

ganglion

Superior vagal

ganglion

Pulmonary plexus

Liver

Cardiac

branch

Sternocleidomastoid

muscle

Accessory nerve

Cranial roots of

accessory nerve

Spinal roots of accessory nerve

To soft palate and pharyngeal muscles

To sternocleidomastoid and trapezius muscles

Cervical

spinal

nerves

External branch

of accessory nerve

Trapezius

muscle

continued

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Chapter 13 Brain and Cranial Nerves 457

DentalAnesthesia

Dentistsinject anesthetic to block sensory transmission bythe alveolar

nerves. The superior alveolar nervesare not usually anesthetized directly

because theyare difﬁcult to approach with a needle. For this reason, the

maxillaryteeth are usually anesthetized locally byinser ting the needle

beneath the oralmucosa surrounding the teeth. The inferior alveolar

nerve probablyis anesthetized more often than any other nerve in the

body. To anesthetize thisnerve, the dentistinserts the needle somewhat

posterior to the patient’slast molar.

Severalnondental nerves are usually anesthetized during an

inferior alveolar block. The mentalnerve, which suppliescutaneous

innervation to the anterior lip and chin, isa distal branch ofthe inferior

alveolar nerve. When the inferior alveolar nerve isblocked, the mental

nerve isblocked also, resulting in a numb lip and chin. Nerves lying near

the pointwhere the inferior alveolar nerve enters the mandible often are

also anesthetized during inferior alveolar anesthesia. For example, the

lingualnerve can be anesthetized to produce a numb tongue. The facial

nerve liessome distance from the inferior alveolar nerve, but in rare cases

anestheticcan diffuse far enough posteriorly to anesthetize that nerve. The

resultis a temporary facial palsy (paralysisor paresis), with the injected

side ofthe face drooping because of ﬂaccid muscles, which disappears

when the anesthesia wearsoff. If the facialner ve iscut by an improperly

inserted needle, permanentfacial palsy may occur.

Theabducens (ab-doosenz)nerve (VI), like the trochlear nerve,

is a somatic motor nerve that innervates one ofthe six eye muscles

responsible for moving the eyeball.

PREDICT

A drooping upper eyelid on one side ofthe face is a sign of possible

oculomotor nerve damage. Describe how thiscould possibly be

evaluated byexamining other oculomotor nerve functions. Describe

the movementsof the eye that would distinguish among oculomotor,

trochlear, and abducensnerve damage.

The facial nerve (VII) is somatic motor, sensory, and

parasympathetic.It controls all the muscles of facial expression, a

small muscle in the middle ear,and two throat muscles. It is sen-

sory for the sense of taste in the anterior two-thirds of the tongue

(see chapter 15).The facial nerve supplies parasympathetic inner-

vation to the submandibular and sublingual salivary glands and to

the lacrimal glands.

The vestibulocochlear (ves-tibu¯-lo¯-kokle¯-a˘r) ner ve

(VIII), like the olfactory and optic nerves, is exclusively sensory

and transmits action potentials from the inner ear responsible for

the special senses ofhearing and balance (see chapter 15).

The glossopharyngeal (gloso¯-fa˘-rinje¯-a˘l) nerve (IX),

like the facial nerve,is somatic motor, sensory, and parasympa-

thetic and has both sensory and parasympathetic ganglia. The

Table 13.5

Cranial Nerve Foramen or Fissure* Function

XII: Hypoglossal Hypoglossal canal Motor

†

Motor to intrinsic and extrinsic tongue muscles (styloglossus,

hypoglossus, genioglossus) and throat muscles (thyrohyoid and

geniohyoid)

Proprioceptive from those muscles

continued

Hypoglossal nerve

Lingual branch of

trigeminal nerve

To tongue muscles

To geniohyoid muscle

(cervical nerves

running with

hypoglossal)

To thyrohyoid muscle

(cervical nerves

running with

hypoglossal)

Ansa cervicalis to

infrahyoid muscles

(cervical nerves

running with

hypoglossal)

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glossopharyngeal nerve is somatic motor to one muscle of the phar-

ynx and supplies parasympathetic innervation to the parotid salivary

glands.The glossophar yngeal nerve is sensory for the sense of taste

in the posterior third ofthe tongue. It also supplies tactile sensory in-

nervation from the posterior tongue,middle ear, and pharynx and

transmits sensory stimulation from receptors in the carotid arteries

and the aortic arch,which monitor blood pressure and blood carbon

dioxide,blood oxygen, and blood pH levels (see chapter 21).

Thevagus (va¯gu˘s)nerve (X), like the facial and glossopha-

ryngeal nerves, is somatic motor,sensor y,and parasympathetic

and has both sensory and parasympathetic ganglia. Most muscles

ofthe soft palate, pharynx, and larynx are innervated by the vagus

nerve.Damage to the laryngeal branches of the vagus nerve can in-

terfere with normal speech. The vagus nerve is sensory for taste

from the root ofthe tongue (see chapter 15). It’s sensory for the in-

ferior pharynx and the larynx and assists the glossopharyngeal

nerve in transmitting sensory stimulation from receptors in the

carotid arteries and the aortic arch,which monitor blood pressure

and carbon dioxide,oxygen, and pH levels in the blood (see chap-

ter 21).In addition, the vagus nerve conveys sensory information

from the thoracic and abdominal organs. The parasympathetic

part of the vagus nerve is very important in regulating the func-

tions of the thoracic and abdominal organs.It carries par asympa-

thetic ﬁbers to the heart and lungs in the thorax and to the

digestive organs and kidneys in the abdomen.

The accessory (XI) and hypoglossal (XII) nerves are so-

matic motor nerves.The accessory nerve has both a cranial and a

spinal component. The cranial component joins the vagus nerve

(hence the name accessory) and participates in its function. The

spinal component ofthe accessory nerve provides the major inner-

vation to the sternocleidomastoid and trapezius muscles of the

neck and shoulder. The hypoglossal nerve supplies the intrinsic

tongue muscles,three of the four extrinsic tongue muscles, and the

thyrohyoid and the geniohyoid muscles.

20. What are the three major functions of the cranial nerves?

21. Which cranial nerves are sensory only? With what sense is

each of these nervesassociated?

22. Name the cranial nerves that are somatic motor and

proprioceptive only. Whatmuscles or muscle groups does

each nerve supply?

23. The sensory cutaneous innervation of the face is provided

bywhat cranial nerve? How is this nerve important in

dentistry? Name the musclesthat would not function if this

nerve wasdamaged.

24. Which four cranial nerves have a parasympathetic function?

Describe the function of each of these nerves.

25. Name the cranial nerves that control the movement of the

eyeball.

Part3 Integration and ControlSystems458

26. Which cranial nerves are involved in the sense of taste?

Whatpart of the tongue does each supply?

27. Speech production involves which cranial nerves? Describe

the branchesof these nerves.

PREDICT

Injuryto the spinal portion of the accessory nerve may resultin

sternocleidomastoid muscle dysfunction, a condition called “wry

neck.” Ifthe head of a person with wry neckis turned to the left,

would thisposition indicate injury to the left or right spinal

componentof the accessory nerve?

PREDICT

Unilateraldamage to the hypoglossal nerve results in loss of tongue

movementon one side, which is most obvious when the tongue is

protruded. Ifthe tongue is deviated to the right, is the left or right

hypoglossalnerve damaged?

Reﬂexesin the Brainstem Involving

CranialNerves

Reﬂexes integrated within the spinal cord were discussed in chap-

ter 12.Many of the body’s functions, especially those involved in

maintaining homeostasis, involve reﬂexes that are integrated

within the brain.Some of these reﬂexes,such as those involved in

the control ofheart rate (see chapter 20), blood pressure (see chap-

ter 21), and respiration (see chapter 23), are integrated in the

brainstem and many involve cranial nerve X (vagus nerve).

Many of the brainstem reﬂexes are associated with cranial

nerve function.The circuitry of most of these reﬂexes is too com-

plex for our discussions, but some general outlines can be pre-

sented. These reflexes involve sensory input from the cranial

nerves or spinal cord,and the motor output of the motor cranial

nerves.

Turning ofthe eyes toward a ﬂash of light, sudden noise, or a

touch on the skin are examples ofbr ainstem reﬂexes.Moving the

eyes to track a moving object is another,complex brainstem reﬂex.

Some of the sensory neurons from cranial nerve VIII form a re-

ﬂex arc with neurons ofcranial nerves V and VII, which send axons

to muscles ofthe middle ear and dampen the effects of very loud,

sustained noises on delicate inner ear structures (see chapter 15).

Reﬂexes that occur during the process ofchewing allow the jaws to

react to foods of various hardness and protect the teeth from

breakage from very hard food items.Both the sensory and motor

components ofthe reﬂex arc are carried by cranial nerve V.Reﬂexes

involving input through cranial nerve V and output through cra-

nial nerve XII move the tongue about to position food between the

teeth for chewing and then move the tongue out of the way so it

isn’t bitten!

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Clinical Focus PeripheralNervous System Disorders

—

CranialNerves

General issues of PNS disorders are de-

scribed in chapter 12. Thischapter addresses

onlythose speciﬁc to the cranial nerves.

Trigeminal neuralgia, also called tic

douloureux, involves one or more of the

trigeminal nerve branches and consistsof

sharp burstsof pain in the face. This disor-

der often has a trigger pointin or around

themouth, which, when touched, elicits the

pain response in some other part of the

face. The cause oftrigeminal neuralgia is

unknown.

Facial palsy (called Bell’s palsy) is a

unilateral paralysis of the facial muscles.

The affected side of the face droops be-

cause ofthe absence of muscle tone. Facial

palsyinvolves the facial nerve and may re-

sultfrom facial nerve neuritis.

Infections

Herpessimplex I is usuallycharacterized by

one or more lesions (sores) on the lips or

nose. The virusapparently remain dormant

in the trigeminal ganglion. Eruptions are

usuallyrecurrent and often occur in times of

reduced resistance, such asduring a case

of the common cold. For thisreason they

are called cold soresor fever blisters.

Geneticand Autoimmune

Disorders

Neuroﬁbromatosis(nooro¯-fı¯-bro¯-ma˘-to¯sis)

is a genetic disorder in which smallskin

lesionsappear in early childhood followed

by the development of multiple subcuta-

neous neurofibromas, which are benign

tumorsresulting from Schwann cell prolif-

eration. The neuroﬁbromasmay slowly in-

crease in size and number over several

yearsand cause extreme disﬁguration.

Chapter 13 Brain and Cranial Nerves 459

Brainstem

(p. 434)

Medulla Oblongata

1. The medulla oblongata is continuous with the spinal cord and

contains ascending and descending nerve tracts.

2. The pyramids are nerve tracts controlling voluntary muscle

movement.

3. The olives are nuclei that function in equilibrium,coordination, and

modulation ofsound from the inner ear.

4. Medullary nuclei regulate the heart,blood vessels, respiration,

swallowing,vomiting, coughing, sneezing, and hiccuping. The

nuclei ofcranial nerves V and IX–XII are in the medulla.

Pons

1. The pons is superior to the medulla.

2. Ascending and descending nerve tracts pass through the pons.

3. Pontine nuclei regulate sleep and respiration.The nuclei of cranial

nerves V–IX are in the pons.

Midbrain

1. The midbrain is superior to the pons.

2. The midbrain contains the nuclei for cranial nerves III,IV,and V.

3. The tectum consists offour colliculi. The two inferior colliculi are

involved in hearing and the two superior colliculi in visual reﬂexes.

4. The tegmentum contains ascending tracts and the red nuclei,which

are involved in motor activity.

5. The cerebral peduncles are the major descending motor pathway.

6. The substantia nigra connects to other basal nuclei and is involved

with muscle tone and movement.

Reticular Formation

The reticular formation consists ofnuclei scattered throughout the brain-

stem.The reticular-activating system extends to the thalamus and cere-

brum and maintains consciousness.

Cerebellum

(p. 437)

1. The cerebellum has three parts that control balance,gross motor

coordination,and ﬁne motor coordination.

2. The cerebellum functions to correct discrepancies between intended

movements and actual movements.

3. The cerebellum can “learn”highly speciﬁc complex motor activities.

Diencephalon

(p. 439)

The diencephalon is located between the brainstem and the cerebrum.

Thalamus

1. The thalamus consists oftwo lobes connected by the intermediate

mass.The thalamus functions as an integration center.

2. Most sensory input synapses in the thalamus.

3. The thalamus also has some motor functions.

Subthalamus

The subthalamus is inferior to the thalamus and is involved in motor func-

tion.

Epithalamus

The epithalamus is superior and posterior to the thalamus and contains

the habenular nuclei, which inﬂuence emotions through the sense of

smell.The pineal body may play a role in the onset of puberty.

Hypothalamus

1. The hypothalamus,the most inferior portion of the diencephalon,

contains several nuclei and tracts.

2. The mamillary bodies are reﬂex centers for olfaction.

3. The hypothalamus regulates many endocrine functions (e.g.,

metabolism,reproduction, response to stress, and urine

production).The pituitary gland attaches to the hypothalamus.

4. The hypothalamus regulates body temperature,hunger, thirst,

satiety,swallowing, and emotions.

Cerebrum

(p. 441)

1. The cortex ofthe cerebrum is folded into ridges called gyri and

grooves called sulci,or ﬁssures.

2. The longitudinal ﬁssure divides the cerebrum into left and right

hemispheres.Each hemisphere has ﬁve lobes.

• The frontal lobes are involved in smell,voluntary motor function,

motivation,aggression, and mood.

SUMMARY

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• The parietal lobes contain the major sensory areas receiving

general sensory input,taste, and balance.

• The occipital lobes contain the visual centers.

• The temporal lobes receive olfactory and auditory input and are

involved in memory,abstract thought, and judgment.

3. Nerve tracts connect areas ofthe cortex within the same hemisphere

(association ﬁbers),between different hemispheres (commissural

ﬁbers),and with other parts of the brain and the spinal cord

(projection ﬁbers).

BasalNuclei

1. Basal nuclei include the subthalamic nuclei,substantia nigra, and

corpus striatum.

2. The basal nuclei are important in controlling motor functions.

LimbicSystem

1. The limbic system includes parts ofthe cerebral cortex, basal nuclei,

thalamus,hypothalamus, and the olfactory cortex.

2. The limbic system controls visceral functions through the

autonomic nervous system and the endocrine system and is also

involved in emotions and memory.

Meningesand Cerebrospinal Fluid

(p. 444)

Meninges

1. The brain and spinal cord are covered by the dura,arachnoid, and

pia mater.

2. The dura mater attaches to the skull and has two layers that can

separate to form dural sinuses.

3. Beneath the arachnoid mater the subarachnoid space contains CSF

that helps cushion the brain.

4. The pia mater attaches directly to the brain.

Ventricles

1. The lateral ventricles in the cerebrum are connected to the third

ventricle in the diencephalon by the interventricular foramen.

2. The third ventricle is connected to the fourth ventricle in the pons

by the cerebral aqueduct.The central canal of the spinal cord is

connected to the fourth ventricle.

CerebrospinalFluid

1. CSF is produced from the blood in the choroid plexus ofeach

ventricle.CSF moves from the lateral to the third and then to the

fourth ventricle.

2. From the fourth ventricle CSF enters the subarachnoid space

through three foramina.

3. CSF leaves the subarachnoid space through arachnoid granulations

and returns to the blood in the dural sinuses.

Part3 Integration and ControlSystems460

Blood Supplyto the Brain

(p. 448)

1. The brain receives blood from the internal carotid and vertebral

arteries.The latter form the basilar artery. The basilar and internal

carotid arteries contribute to the cerebral arterial circle.Branches

from the circle and basilar artery supply the brain.

2. The blood–brain barrier is formed from the endothelial cells ofthe

capillaries in the brain,the astrocytes in the brain tissue, and the

basement membrane in between.

Developmentof the CNS

(p. 449)

The brain and spinal cord develop from the neural tube.The ventricles

and central canal develop from the lumen ofthe neural tube.

CranialNerves

(p. 449)

1. Cranial nerves perform sensory,somatic motor, proprioceptive,and

parasympathetic functions.

2. The olfactory (I) and optic (II) nerves are involved in the sense of

smell and vision.

3. The oculomotor nerve (III) innervates four ofsix extrinsic e ye

muscles and the upper eyelid.The oculomotor nerve also provides

parasympathetic supply to the iris and lens ofthe eye.

4. The trochlear nerve (IV) controls an extrinsic eye muscle.

5. The trigeminal nerve (V) supplies the muscles of mastication, as well

as a middle ear muscle,a palatine muscle, and two throat muscles.

The trigeminal nerve has the greatest cutaneous sensory distribution

ofany cranial nerve. The trigeminal nerve has three branches. Two of

the three trigeminal nerve branches innervate the teeth.

6. The abducens nerve (VI) controls an extrinsic eye muscle.

7. The facial nerve (VII) supplies the muscles offacial expression, an

inner ear muscle,and two throat muscles. It is involved in the sense

oftaste. It’s parasympathetic to two sets of salivary glands and to the

lacrimal glands.

8. The vestibulocochlear nerve (VIII) is involved in the sense of

hearing and balance.

9. The glossopharyngeal nerve (IX) is involved in taste and supplies

tactile sensory innervation from the posterior tongue,middle ear,

and pharynx.It’s also sensory for receptors that monitor blood

pressure and gas levels in the blood.The glossopharyngeal nerve is

parasympathetic to the parotid salivary glands.

10. The vagus nerve (X) innervates the muscles ofthe phar ynx,palate,

and larynx.It’s also involved in the sense of taste.The vagus ner ve is

sensory for the pharynx and larynx and for receptors that monitor

blood pressure and gas levels in the blood.The vagus nerve is sensory

for thoracic and abdominal organs.The vagus nerve provides

parasympathetic innervation to the thoracic and abdominal organs.

11. The accessory nerve (XI) has a cranial and a spinal component.The

cranial component joins the vagus nerve.The spinal component

supplies the sternocleidomastoid and trapezius muscles.

12. The hypoglossal nerve (XII) supplies the intrinsic tongue muscles,

three offour extrinsic tongue muscles, and two throat muscles.

Reﬂexesin the Brainstem Involving Cranial Nerves

Many reﬂexes involved in homeostasis involve the cranial nerves and occur

in the brainstem.

1. Ifa section is made that separates the brainstem from the rest of the

brain,the cut is between the

a. medulla oblongata and pons.

b. pons and midbrain.

c. midbrain and diencephalon.

d. thalamus and cerebrum.

e. medulla oblongata and spinal cord.

2. Important centers for heart rate,blood pressure, respiration,

swallowing,coughing, and vomiting are located in the

a. cerebrum.

b. medulla oblongata.

c. midbrain.

d. pons.

e. cerebellum.

REVIEW AND COMPREHENSION

Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

III. Integration and Control

Systems

13. Brain and Cranial

Nerves

Companies, 2004

Chapter 13 Brain and Cranial Nerves 461

3. In which ofthese parts of the brain does decussation ofdescending

nerve tracts involved in the conscious control ofskeletal muscles

occur?

a. cerebrum

b. diencephalon

c. midbrain

d. pons

e. medulla oblongata

4. Important respiratory centers are located in the

a. cerebrum.

b. cerebellum.

c. pons and medulla oblongata.

d. midbrain

e. limbic system.

5. The cerebral peduncles are a major descending motor pathway

found in the

a. cerebrum.

b. cerebellum.

c. pons.

d. midbrain.

e. medulla oblongata.

6. The superior colliculi are involved in ,whereas the

inferior colliculi are involved in .

a. hearing,visual reﬂexes

b. visual reﬂexes,hearing

c. balance,motor pathways

d. motor pathways,balance

e. respiration,sleep

7. The cerebellum communicates with other regions ofthe CNS

through the

a. ﬂocculonodular lobe.

b. cerebellar peduncles.

c. vermis.

d. lateral hemispheres.

e. folia.

8. The major relay station for sensory input that projects to the

cerebral cortex is the

a. hypothalamus.

b. thalamus.

c. pons.

d. cerebellum.

e. midbrain.

9. Which part ofthe brain is involved with olfactory reﬂexes and

emotional responses to odors?

a. inferior colliculi

b. superior colliculi

c. mamillary bodies

d. pineal body

e. pituitary gland

10. The part ofthe diencephalon directly connected to the pituitary

gland is the

a. hypothalamus.

b. epithalamus.

c. subthalamus.

d. thalamus.

11. Which ofthe following is a function of the hypothalamus?

a. regulates autonomic nervous system functions

b. regulates the release ofhormones from the posterior pituitary

c. regulates body temperature

d. regulates food intake (hunger) and water intake (thirst)

e. all ofthe above

12. The grooves on the surface ofthe cerebrum are called the

a. nuclei.

b. commissures.

c. tracts.

d. sulci.

e. gyri.

13. Which ofthese areas is located in the postcentral gyrus of the

cerebral cortex?

a. olfactory cortex

b. visual cortex

c. primary motor cortex

d. primary somatic sensory cortex

e. primary auditory cortex

14. Which ofthese cerebral lobes is important in voluntary motor

function,motivation, aggression, sense of smell, and mood?

a. frontal

b. insula

c. occipital

d. parietal

e. temporal

15. Fibers that connect areas ofthe cerebral cortex within the same

hemisphere are

a. projection ﬁbers.

b. commissural ﬁbers.

c. association ﬁbers.

d. all ofthe above.

16. The basal nuclei are located in the

a. inferior cerebrum

b. diencephalon

c. midbrain

d. all ofthe above

17. The most superﬁcial ofthe meninges is a thick, tough membrane

called the

a. pia mater.

b. dura mater.

c. arachnoid mater.

d. epidural mater.

18. The ventricles ofthe brain are interconnected. Which of these

ventricles are notcorrectly matched with the structures that connect

them?

a. lateral ventricle to the third ventricle—interventricular foramina

b. left lateral ventricle to right lateral ventricle—central canal

c. third ventricle to fourth ventricle—cerebral aqueduct

d. fourth ventricle to subarachnoid space—median and lateral

apertures

19. Cerebrospinal ﬂuid is produced by the ,circulates

through the ventricles,and enters the subarachnoid space. The

cerebrospinal ﬂuid leaves the subarachnoid space through the

a. choroid plexuses,arachnoid granulations

b. arachnoid granulations,choroid plexuses

c. dural sinuses,dura mater

d. dura mater,dural sinuses

20. Given these spaces:

1. third ventricle

2. epidural space

3. subarachnoid space

4. subdural space

5. superior sagittal sinus

Which ofthese spaces contains cerebrospinal ﬂuid (CSF)?

a. 1,3

b. 1,2,3

c. 1,3,5

d. 1,2,3,5

e. 2,3,4,5

Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

III. Integration and Control

Systems

13. Brain and Cranial

Nerves

Companies, 2004

21. Water-soluble molecules such as glucose and amino acids move

across the blood–brain barrier by

a. diffusion.

b. endocytosis.

c. exocytosis.

d. mediated transport.

e. ﬁltration.

22. Which ofthese parts of the embr yonic brain is correctly matched

with the structure it becomes in the adult brain?

a. mesencephalon—midbrain

b. metencephalon—medulla oblongata

c. myelencephalon—cerebrum

d. telencephalon—pons and cerebellum

23. The cranial nerve involved in chewing food is the

a. trochlear (IV).

b. trigeminal (V).

c. abducens (VI).

d. facial (VII).

e vestibulocochlear (VIII).

24. The cranial nerve responsible for focusing the eye (innervates the

ciliary muscle ofthe eye) is the

a. optic (II).

b. oculomotor (III).

c. trochlear (IV).

d. abducens (VI).

e. facial (VII).

25. The cranial nerve involved in moving the tongue is the

a. trigeminal (V).

b. facial (VII).

c. glossopharyngeal (IX).

d. accessory (XI).

e. hypoglossal (XII).

26. The cranial nerve involved in feeling a toothache is the

a. trochlear (IV).

b. trigeminal (V).

c. abducens (VI).

d. facial (VII).

e. vestibulocochlear (VIII).

27. From this list ofcranial nerves:

1. olfactory (I)

2. optic (II)

3. oculomotor (III)

4. abducens (VI)

5. vestibulocochlear (VIII)

Select the nerves that are sensory only.

a. 1,2,3

b. 2,3,4

c. 1,2,5

4. 2,3,5

5. 3,4,5

Part3 Integration and ControlSystems462

28. From this list ofcranial nerves:

1. optic (II)

2. oculomotor (III)

3. trochlear (IV)

4. trigeminal (V)

5. abducens (VI)

Select the nerves that are involved in moving the eyes.

a. 1,2,3

b. 1,2,4,

c. 2,3,4

d. 2,4,5

e. 2,3,5

29. From this list ofcranial nerves:

1. trigeminal (V)

2. facial (VII)

3. glossopharyngeal (IX)

4. vagus (X)

5. hypoglossal (XII)

Select the nerves that are involved in the sense oftaste.

a. 1,2,3

b. 1,4,5

c. 2,3,4

d. 2,3,5

e. 3,4,5

30. From this list ofcranial nerves:

1. trigeminal (V)

2. facial (VII)

3. glossopharyngeal (IX)

4. vagus (X)

5. hypoglossal (XII)

Select the nerves that innervate the salivary glands.

a. 1,2

b. 2,3

c. 3,4

d. 4,5

e. 3,5

31. From this list ofcranial nerves:

1. oculomotor (III)

2. trigeminal (V)

3. facial (VII)

4. vestibulocochlear (VIII)

5. glossopharyngeal (IX)

6. vagus (X)

Select the nerves that are part ofthe parasympathetic division of the

ANS.

a. 1,2,4,5

b. 1,3,5,6

c. 1,4,5,6

d. 2,3,4,5

e. 2,3,5,6

Answers in Appendix F

1. A patient looses all sense offeeling in the left side of the back,below

the upper limb,and extending in a band around to the chest, also

below the upper limb.All sensation on the right is normal. The line

between normal and absent sensation is the anterior and posterior

midline.Explain this condition.

2. The cerebral cortex ofhumans is highly convoluted. What advantage

does this provide?

3. What happens to the developing brain ifthe CSF is not properly

drained,resulting in early hydrocephalus?

4. A patient exhibits enlargement ofthe lateral and third ventricles, but

no enlargement ofthe fourth ventricle. What would you conclude?

5. During a spinal tap ofa patient, blood is discovered in the CSF.

What does this ﬁnding suggest?

Answers in Appendix G

CRITICAL THINKING

Seeley−Stephens−Tate:

Anatomy and Physiology,

Sixth Edition

III. Integration and Control

Systems

13. Brain and Cranial

Nerves

Companies, 2004

Chapter 13 Brain and Cranial Nerves 463

1. The oculomotor nerve innervates four eye muscles and the levator

palpebrae superioris muscle.One cause of ptosis, a drooping upper

eyelid,can be oculomotor nerve damage and subsequent paralysis of

the levator palpebrae superioris muscle.The four eye muscles

innervated by the oculomotor nerve move the eyeball so that the

gaze is directed superiorly,inferiorly,medially, or superolaterally.

Damage to this nerve can be tested by having the patient look in

these directions.The abducens nerve directs the gaze laterally,and

the trochlear nerve directs the gaze inferolaterally.If the patient can

move the eyes in these directions,the associated nerves are intact.

2. The sternocleidomastoid muscle pulls the mastoid process (located

behind the ear) toward the sternum,thus turning the face to the

opposite side.If the innervation to one sternocleidomastoid muscle

is eliminated (accessory nerve injury),the opposite muscle is

unopposed and turns the face toward the side ofinjury. A person

with wry neck whose head is turned to the left most likely has an

injured left accessory nerve.

3. The tongue is protruded by contraction ofthe geniohyoid muscle,

which pulls the back ofthe tongue forward, thereby pushing the

muscle mass ofthe tongue forward. With one side pushed forward

and unopposed by muscles ofthe opposite side, the tongue deviates

toward the nonfunctional side.In the example, therefore,the rig ht

hypoglossal nerve is damaged.

ANSWERS TO PREDICT QUESTIONS

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