Chapter 15
*Lecture Outline
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Chapter 15 Outline
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Brain and Tissue Development
Support and Protection of the Brain
Cerebrum
Diencephalon
Brainstem
Cerebellum
Limbic System
Cranial Nerves
Human Brain Size
• Volume: 1200–1500 cc
• Weight: 1.35–1.4 kg
Major Regions of Human Brain
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Cerebrum
Diencephalon
Brainstem
Cerebellum
Major Parts of Adult Brain
Figure 15.1
Major Parts of Adult Brain
Figure 15.1
Major Parts of Adult Brain
Figure 15.1
The Cerebrum-Lobes
Motor Cortex
Sensory Cortex
Directional Terms
to Describe the Brain
• Rostral —toward the nose (synonymous
with anterior)
• Caudal —toward the tail (synonymous
with posterior)
Embryonic Development
of the Brain
By the late fourth week of development
three primary brain vesicles have
formed:
1. Prosencephalon (forebrain)
2. Mesencephalon (midbrain)
3. Rhombencephalon (hindbrain)
Developing Human Brain
(Four Weeks)
Figure 15.2
Embryonic Development
of the Brain
By the fifth week of development, the three primary
vesicles further develop into five secondary brain
vesicles:
1. Telencephalon—arises from prosencephalon, eventually forms
cerebrum
2. Diencephalon—derives from prosencephalon, eventually forms
thalamus, hypothalamus, and epithalamus
3. Mesencephalon—only primary vesicle that does not form a new
secondary vesicle
4. Metencephalon—arises from rhombencephalon, eventually
forms the pons and cerebrum
5. Myelencephalon—derives from rhombencephalon, eventually
forms medulla oblongata
Developing Human Brain
(Fifth Week)
Figure 15.2
Developing Human Brain
Figure 15.2
Developing Human Brain
Figure 15.2
Developing Human Brain
Figure 15.2
Developing Human Brain
Organization of Neural Tissue
Areas in the Brain
Gray matter:
• houses motor neuron and interneuron cell bodies,
dendrites, telodendria, unmyelinated axons
• forms the cortex, which covers the surface of most of
the adult brain
• forms discrete internal clusters called cerebral
nuclei
White matter:
• made up of myelinated axons
• lies deep to the gray matter of the cortex
Organization of Neural Tissue
Areas in the Brain
Support and Protection
of the Brain
Cranial meninges are connective tissue layers that:
• Separate soft tissue of the brain from bones of
cranium
• enclose and protect blood vessels that supply the
brain
• contain and circulate cerebrospinal fluid
• form some of the veins that drain blood from the brain
• the layers are:
– dura mater
– arachnoid mater
– pia mater
Cranial Meninges
Figure 15.4
Cranial Dural Septa
There are four cranial dural septa that partition separate
specific parts of the brain and provide stabilization and support:
1. Falx cerebri—projects into longitudinal fissure and
separates left and right cerebral hemispheres
2. Tentorium cerebelli—horizontal fold that separates
cerebrum from cerebellum; anterior surface has a gap
(tentorial notch) to allow for passage of
brainstem
3. Falx cerebelli—partition that separates left and right
cerebellar hemispheres
4. Diphragma selae—small septum between pituitary and
hypothalamus
Dural Venous Sinuses
The dural venous sinuses run within the
margins of the dural septa.
• Superior sagittal sinus—runs within the superior
margin of the falx cerebri
• Inferior sagittal sinus—runs within the inferior
margin of the falx cerebri
• Transverse sinuses—run within the posterior border
of the tentorium cerebelli
• Occipital sinus—runs in the posterior vertical border
of the falx cerebelli
Cranial Dural Septa
Figure 15.5
Brain Ventricles
Ventricles are cavities or expansions within the
brain that are continuous with one another and
the central canal of the spinal cord. All
ventricles contain cerebral spinal fluid. There
are four ventricles in the brain:
• Two lateral ventricles, one in each
hemisphere of the cerebrum, separated by a
thin septum pellucidum
• A third ventricle in the diencephalon
• A fourth ventricle between the pons and
cerebellum
Ventricles of the Brain
Figure 15.6
Cerebrospinal Fluid
Cerebrospinal fluid (CSF) is a clear, colorless
liquid that circulates in the ventricles and
subarachnoid space. Several important
functions of CSF are:
• Buoyancy—the brain floats in the CSF
• Protection—CSF provides a liquid cushion
from sudden movements
• Environmental stability—CSF transports
nutrients and removes waste from the brain
Cerebral Spinal Fluid Formation
in the Choroid Plexus
Figure 15.7
Figure 15.8
Blood-Brain Barrier
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The blood brain barrier (BBB) strictly
regulates what substances can enter the
interstitial fluids of the brain.
Capillary endothelial cells and astrocyte
perivascular feet contribute to the BBB.
The BBB is markedly missing or reduced in
three distinct locations of the CNS:
– choroid plexus
– hypothalamus
– pineal gland
Blood-Brain Barrier
Figure 15.9
Cerebrum
• The cerebrum is the location of
conscious thought processes and the
origin of intellectual functions.
• The cerebrum contains a large number
of neurons that are needed for complex
analytical and integrative functions.
Cerebrum
• The outer layer is called the cerebral
cortex and is gray matter. The internal
layer is white matter.
• Deep to the white matter are discrete
regions of gray matter called cerebral
nuclei.
• The surface of the cerebrum folds into
elevated ridges called gyri.
• Adjacent gyri are separated by shallow
sulci or deeper grooves called
fissures.
The Cerebrum –Basal Nuclei
Cerebral Hemispheres
• The cerebrum is composed of two halves called
left and right cerebral hemispheres.
• The paired cerebral hemispheres are divided by
a longitudinal fissure that extends along the
midsagittal plane.
• The hemispheres are separate from one another
except at a few locations where bundles of axons
called tracts form white matter regions that allow
for communication between them.
• The corpus callosum is the largest tract and the
main tract that connects the two hemispheres.
Cerebral Hemispheres
• Considerable overlap and indistinct boundaries
permit a single region of the cortex to exhibit several
different functions.
• Some aspects of cortical function, such as memory or
consciousness, cannot easily be assigned to any
single region.
• With few exceptions, both cerebral hemispheres
receive their sensory information from and project
motor commands to the opposite sides of the body.
• The two hemispheres appear as anatomic mirror
images, but they display some functional differences,
termed hemisphere lateralization.
Lobes of the Cerebrum
Each hemisphere is divided into five
anatomically distinct lobes:
1. Frontal Lobe
2. Parietal Lobe
3. Temporal Lobe
4. Occipital Lobe
5. Insula
Cerebral Hemispheres
Figure 15.10
Cerebral Lobes
Figure 15.11
Frontal Lobe
• Located deep to the frontal bone and forms
anterior part of cerebral hemisphere
• Ends posteriorly at the central sulcus;
inferior border marked by the lateral sulcus
• Precentral gyrus is a mass of nervous tissue
in the frontal lobe immediately anterior to the
central sulcus
• Involved with voluntary motor function,
concentration, verbal communication,
decision making, planning, and
personality
Parietal Lobe
• Forms the superoposterior part of each
hemisphere and underlies the parietal bone
• Terminates anteriorly at the central sulcus,
laterally at the lateral sulcus, and posteriorly
at the parieto-occipital sulcus
• Postcentral gyrus is a mass of nervous
tissue in the parietal lobe immediately
posterior to central sulcus
• Involved with general sensory functions
Temporal Lobe
• Located inferior to the lateral sulcus
underlying the temporal bone
• Involved with hearing and smell
Occipital Lobe
• Located in the posterior region of each
hemisphere underlying the occipital
bone
• Processes incoming visual
information
• Stores visual memories
Insula
• Located deep to the lateral sulcus
• Involved in memory and interpretation of
taste
Functional Areas of
Cerebrum
Three categories of functional areas are
recognized:
1. Motor areas—control voluntary motor
functions
2. Sensory areas—provide conscious
awareness of sensation.
3. Association areas—integrate and
store information
Motor Areas
• Primary Motor Cortex (somatic motor area)—
controls voluntary skeletal muscle activity; located
within the precentral gyrus; axons project
contralaterally to the brainstem and spinal cord;
innervation to various body parts can be
diagrammed as a motor homunculus on the
precentral gyrus
• Motor Speech Area (Broca’s Area)—controls
muscular movements necessary for vocalization;
located in most individuals within the inferolateral
portion of the left frontal lobe
• Frontal Eye Field—controls and regulates eye
movements and binocular vision; located on the
superior surface of the middle frontal gyrus,
immediately anterior to the premotor cortex
Primary Motor Cortex
Figure 15.12
Sensory Areas
Cortical areas involved with conscious awareness of
sensation:
• Primary somatosensory cortex—receives general
somatic sensory information from touch, pressure, pain,
and temperature receptors; located within the postcentral
gyrus; sensory homunculus may be traced on surface
• Primary visual cortex—receives and processes incoming
visual information; located in occipital lobe
• Primary auditory cortex—receives and processes
auditory information; located in temporal lobe
• Primary gustatory cortex—processes taste information;
located in insula
• Primary olfactory cortex—provides conscious awareness
of smell; located in temporal lobe
Primary Somatosensory Cortex
Figure 15.12
Association Areas
• Premotor cortex (somatic motor association area)—
processes motor information and coordinates learned skilled
motor activities; located in frontal lobe immediately anterior to
precentral gyrus
• Somatosensory association area—integrates and interprets
sensory information; located in parietal lobe immediately
posterior to post central gyrus
• Auditory association area—interprets characteristics of sound
and stores memories of sound; located within temporal lobe
posteroinferior to the primary auditory cortex
• Visual association area—processes visual information; located
in the occipital lobe
• Wernicke’s area—recognizes and comprehends spoken and
written language; typically located within left hemisphere where
it overlaps the parietal and temporal lobes
• Gnostic area (common integrative area)—integrates all
sensory, visual, and auditory information; composed of regions
of the parietal, occipital, and temporal lobes
Higher-Order Processing
Centers
• Process incoming information from several
different association areas
• Ultimately direct either extremely complex
motor activity or complicated analytical
functions
• Involve functions such as speech, cognition,
understanding spatial relationships, and
general interpretation
• Housed in both cerebral hemispheres
Central White Matter
Central White Matter
Figure 15.13
Cerebral Nuclei
Cerebral nuclei are paired irregular masses of gray matter
buried deep within the central white matter in the basal region of
the cerebral hemispheres inferior to the floor of the lateral
ventricles. They contain the following components:
• Caudate nucleus—produces patterned arm and leg
movements associated with walking
• Amygdaloid body—expression of emotions, control of
behavioral activities, development of moods
• Lentiform nucleus is composed of:
– putamen—subconscious muscular movement
– globus pallidus—excites and inhibits activities of thalamus to
control and adjust muscle tone
• Claustrum—processes visual information at a subconscious
level
• Corpus Striatum—striped appearance of internal capsule as
it passes among the caudate nucleus and lentiform nucleus
Cerebral Nuclei
Figure 15.14
Diencephalon
Components of the diencephalon include:
• Epithalamus
• Thalamus
• Hypothalamus
Diencephalon
Figure 15.15
Epithalamus
• Partially forms posterior roof of the
diencephalon and covers the third ventricle;
components include:
– pineal gland, which secretes melatonin, a
hormone that helps regulate day–night cycles
(circadian rhythm)
– habenular nuclei, which help relay signals from
the limbic system to the mesencephalon and are
involved in visceral and emotional responses to
odor
Thalamus
• The thalamus refers to paired oval masses of gray
matter that lie on each side of the third ventricle.
• A small midline mass of gray matter called the
interthalamic adhesion (or intermediate mass)
connects the right and left thalamic bodies.
• Each part of the thalamus is a gray matter mass
composed of about a dozen or more thalamic nuclei
with axons projecting to particular regions of the
cerebral cortex.
• Sensory impulses from all conscious senses except
olfaction converge on the thalamus and synapse in at
least one of its nuclei.
• The thalamus is a principal and final relay point for
sensory information that will be processed and
projected to the somatosensory cortex.
Thalamus
Figure 15.16
Hypothalamus
• The hypothalamus is the anteroinferior
region of the diencephalon.
• The thin, stalklike infundibulum
extends inferiorly from the
hypothalamus to attach to the pituitary
gland.
Hypothalamus
Figure 15.17
Functions of the Hypothalamus
• Master control of the autonomic
nervous system
• Master control of the endocrine
system
• Regulation of body temperature
• Control of emotional behavior
• Control of food intake
• Control of water intake
• Regulation of sleep–wake (circadian)
rhythms
Brainstem
• Connects the forebrain and cerebellum to the
spinal cord
• Is a bidirectional passageway for all tracts
extending between the cerebrum and the
spinal cord
• Contains many autonomic centers and reflex
centers required for survival
• Houses nuclei of many of the cranial nerves
Brainstem
Three regions form the brainstem:
1. Mesencephalon
2. Pons
3. Medulla Oblongata
Brainstem
Figure 15.18
Mesencephalon
• Superior portion of brainstem
• Cerebral aqueduct extends through the mesencephalon
and connects third and fourth ventricles
– surrounded by periaqueductal gray matter
• Nuclei of oculomotor nerve (CN III) and trochlear nerve
(CN IV) are housed in the mesencephalon
• Somatic motor axons descend from the primary motor
cortex through the cerebral peduncles (located on the
anterolateral surfaces of the mesencephalon) to the spinal
cord
• The superior cerebellar peduncles connect the
cerebellum to the mesencephalon
Mesencephalon
• The tegmentum is between the substantia nigra and the
periaqueductal gray matter. The tegmentum contains the red
nuclei and the reticular formation. The tegmentum integrates
information from the cerebrum and cerebellum and issues
involuntary motor commands to the erector spinae muscles of
the back to maintain posture.
• The substantia nigra consists of bilaterally symmetrical
nuclei with the mesencephalon. The substantia nigra
houses clusters of neurons that produce the
neurotransmitter dopamine, which affects brain processes
that control movement, emotional response, and the ability
to experience pleasure and pain. Degeneration of cells in
the substantia nigra is a pathology that underlies Parkinson
disease.
• The tectum is the posterior region of the mesencephalon dorsal
to the mesencephalic aqueduct. It contains the tectal plate
(quadrigeminal plate) containing the superior colliculi (visual
reflex centers), and the inferior colliculi (auditory reflex
centers).
Mesencephalon
Figure 15.19
Pons
• The pons is a bulging region on the anterior part of the
brainstem that forms from part of the metencephalon.
• Sensory and motor tracts are housed within the pons that
connect to the brain and spinal cord.
• The middle cerebellar peduncles are transverse fibers that
connect the pons to the cerebellum.
• The pons house two autonomic respiratory
centers: the pneumotaxic center and the
apneustic center. These centers regulate the rate
and depth of breathing, and influence the activity
of the respiratory center in the medulla
oblongata.
• The pons houses sensory and motor cranial nerve nuclei for the
trigeminal (CN V), abducens (CN VI), and facial (CN VII) cranial
nerves. Some of the nuclei for the vestibulocochlear cranial
nerve (CN VIII) are located in the pons.
• The superior olivary complex nuclei are located in the pons.
This nuclear complex receives auditory input and involves
pathways for sound localization.
Pons
Figure 15.20
Medulla Oblongata
• The medulla oblongata, the most inferior part of the brainstem,
is formed from the myelencephalon.
• It continues with the spinal cord inferiorly. The caudal portion of
the medulla oblongata resembles the spinal cord.
• The central canal of the spinal cord extends rostrally through the
medulla and enlarges to become the fourth ventricle.
• All communication between the brain and spinal cord involves
tracts that ascend or descend through the medulla oblongata.
• The anterior surface exhibits two longitudinal ridges called the
pyramids, which house the motor projection tracts called the
corticospinal tracts.
• Most of the axons in the pyramids cross to the opposite side at a
point called the decussation of the pyramids, so that each
cerebral hemisphere controls voluntary movement on the
opposite side of the body.
• Paired inferior cerebellar peduncles are tracts that connect
the medulla oblongata to the cerebellum.
Medulla Oblongata
• Immediately lateral to each pyramid is a bulge called the olive,
which contains gray matter called the inferior olivary nucleus.
These nuclei relay ascending sensory impolses, especially
proprioceptive information, to the cerebellar cortex.
• Within the medulla oblongata are cranial nerve nuclei
associated with the vestibulocochlear (CN VIII),
glossopharyngeal (CN IX), vagus (CN X), accessory (CN XI),
and hypoglossal (CN XII) cranial nerves.
• The medulla oblongata contains the nucleus cuneatus and the
nucleus gracilis, which relay somatic sensory information to
the thalamus.
• The nucleus cuneatus receives sensory innervation from the
upper limbs of the same side. The nucleus gracilis receives
sensory innervation from the lower limbs.
• Bands of myelinated fibers composing a medial lemniscus exit
the nucleus cuneatus and the nucleus gracilis and decussate in
the inferior region of the medulla oblongata. The medial
lemniscus projects through the brainstem to the ventral posterior
nucleus of the thalamus.
Medulla Oblongata
The medulla oblongata contains several autonomic
nuclei, which group to form the following centers:
• Cardiac center—regulates heart rate and its
strength of contraction
• Vasomotor center—controls blood pressure by
regulating the contraction and relaxation of smooth
muscle in the walls of arterioles
• Respiratory center—regulates respiratory rate and
is influenced by the apneustic and pneumotaxic
centers of the pons
• Other nuclei—are involved in coughing, sneezing,
salivation, swallowing, gagging, and vomiting
Medulla Oblongata
Figure 15. 21
Cerebellum
• Second largest part of the brain
• Develops from the metencephalon
• Has a complex, highly convoluted surface covered by a layer
of cerebellar cortex with folds called folia
• Composed of left and right cerebellar hemispheres
• Each hemisphere consists of two lobes, anterior lobe and
posterior lobe, separated by primary fissure
• Along the midline, a narrow band of cortex, the vermis,
separates the left and right cerebellar hemispheres. The
vermis receives sensory input on the torso position and
balance. Its output to the vestibular nucleus helps maintain
balance.
• Slender flocculonodular lobes lie anterior and inferior to
each cerebellar hemisphere.
Cerebellum
The cerebellum is partitioned into three
regions:
1. An outer gray matter layer of cortex
2. An internal region of white matter,
called the arbor vitae
3. Cerebellar nuclei in the deepest
layer
Cerebellum
Figure 15.22
Cerebellar Functions
• Coordinates and fine-tunes skeletal muscle
movements and ensures that skeletal muscle
contraction follows the correct pattern leading to
smooth, coordinated movements
• Stores memories of previously learned movement
patterns
• Adjusts skeletal muscle activity to maintain
equilibrium and posture
• Receives proprioceptive (sensory) information from
the muscles and joints and uses this information to
regulate the body’s position
• Monitors the position of each body joint and its
muscle tone
Cerebellar Peduncles
The cerebellar peduncles are three thick tracts
that link the cerebellum with the brainstem.
1. Superior cerebellar peduncles—connect
the mesencephalon to the cerebellum
2. Middle cerebellar peduncles—connect the
pons to the cerebellum
3. Inferior cerebellar peduncles—connect the
medulla oblongata to the cerebellum
Limbic System
• The structures of the limbic system
form a ring around around the
diencephalon.
• The limbic system is composed of multiple
cerebral and diencephalic structures that
collectively process and experience
emotions.
• The limbic system affects memory
formation through the integration of
past memories of physical
sensations with emotional states.
Limbic System
Brain structures commonly recognized to be part
of the limbic system:
• Cingulate gyrus—internal mass of cerebral cortex
located within the longitudinal fissure and superior to
the corpus callosum; receives input from the other
components of the limbic system
• Parahippocampal gyrus—mass of cortical tissue
associated with the hippocampus
• Hippocampus—a nucleus shaped like a seahorse;
essential in storing memories and forming long-term
memory
• Amygdaloid body—involved in several aspects of
emotion, especially fear; helps sort and code memories
based on how they are emotionally perceived
Limbic System
• Olfactory bulbs, olfactory tracts, olfactory
cortex—particular odors can provoke
certain emotions or be associated with
certain emotions
• Fornix—thin tract of white matter that connects
hippocampus with other diencephalon limbic system
structures
• Various nuclei in the diencephalon (anterior
thalamic nuclei, habenular nuclei, septal nuclei,
mammillary bodies)—interconnect other parts of the
limbic system and contribute to overall function
Limbic System
Figure 15.23
Cranial Nerves
• There are 12 pairs of cranial nerves.
• They are numbered with Roman
numerals by their position, beginning
with the most anteriorly placed nerve.
• Their names are generally related to
function.
Cranial Nerves
Figure 15.24
Cranial Nerves
Cranial Nerves
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Table 15.8
Cranial Nerves
CN I OLFACTORY NERVE (ol-fak ́to˘ -re¯; olfacio = to smell)
Olfactory tract
(to cerebral cortex)
Olfactory bulb
Cribriform plate
of ethmoid bone
Axons of olfactory
nerves (CN I)
Description
Sensory function
Conducts olfactory (smell) sensations to brain; only type of nervous tissue to regenerate.
Olfaction (smell)
Origin
Receptors (bipolar neurons) in olfactory mucosa of nasal cavity
Pathway
Travels through the cribri form foramina of ethmoid bone and synapses in the olfactory bulbs, which are located in
the anterior cranial fossa. Within the olfactory bulb, the axons synapse with a smaller number of neurons, the axons
of which form the olfactory tract and project to olfactory cortex
Conditions caused by nerve damage
Anosmia (partial or total loss of smell)
Cranial Nerves
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CN II OPTIC NERVE (op ́tik; ops = eye)
Eye
Optic nerve (CN II)
Optic chiasm
Optic tract
Lateral geniculate
nucleus of thalamus
Optic projection axons
Visual cortex (in occipital lobe)
Description
Sensory function
Origin
Pathway
Conditions caused by nerve damage
Special sensory nerve of vision that is an outgrowth of the brain; more appropriately called a brain tract
Vision
Retina of theeye
Enters cranium via optic canal of sphenoid bone; left and right optic nerves unite at optic chiasm;
optic tract travels to lateral geniculate nucleus of thalamus; finally, information is forwarded to the
occipital lobe
Anopsia (visual defects)
Cranial Nerves
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Table 15.8
Cranial Nerves
CN III OCULOMOTOR NERVE (ok ́u¯ -lo¯-mo¯ ́to˘ r; oculus = eye, motorius = moving)
Levator palpebrae
superioris
Optic
nerve
Superior
rectus
Medial rectus
To ciliary
muscles
Oculomotor
nerve (CNIII)
Ciliary ganglion
Inferior rectus
Inferior oblique
To sphincter
pupillae
Description
Innervates upper eyelid muscle and four of the six extrinsic eye muscles
Somatic motor function
Supplies four extrinsic eye muscles (superior rectus, inferior rectus, medial rectus, inferior oblique) that move eye
Supplies levator palpebrae superioris muscle to elevate eyelid
Parasympathetic motor function
Innervates sphincter pupillae muscle of iris to make pupil constrict
Contracts ciliary muscles to make lens of eye more spherical (as needed for near vision)
Origin
Oculomotor and Edinger Westphal nuclei within mesencephalon
Pathway
Leaves cranium via superior orbital fissure and travels to eye and eyelid. (Parasympathetic fibers travel to ciliary
ganglion, and postganglionic parasympathetic fibers then travel to iris and ciliary muscle.)
Conditions caused by nerve damage
Ptosis (upper eyelid droop); paralysis of most eye muscles, leading to strabismus (eyes not in parallel/deviated
improperly), diplopia (double vision), focusing diffi cultyz
Cranial Nerves
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CN IV TROCHLEAR NERVE (trok ́le¯-ar; trochlea = a pulley)
Optic
nerve (CNII)
Superior
oblique
Trochlear nerve (CNIV)
Description
Innervates one extrinsic eye muscle (superior oblique) that loops through a pulley-shaped ligament
Somatic motor function
Supplies one extrinsic eye muscle (superior oblique) to move eye inferiorly and laterally
Origin
Trochlear nucleus within mesencephalon
Pathway
Leaves cranium via superior orbital fi ssure and travels to superior oblique muscle
Conditions caused by nerve damage
Paralysis of superior oblique, leading to strabismus (eyes not in parallel/deviated improperly), diplopia (double
vision)
Cranial Nerves
Cranial Nerves
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Table 15.8
Cranial Nerves
CN VI ABDUCENS NERVE (ab-doo ́senz; to move away from)
Abducens nerve (CN VI)
Optic nerve
Lateral rectus (cut)
Description
Innervates lateral rectus eye muscle ,which abducts the eye (“pulls away laterally”)
Somatic motor function
Innervates one extrinsic eye muscle (lateral rectus) for eye abduction
Origin
Pontine (abducens) nucleus in pons
Pathway
Leaves cranium through superior orbital fissure and travels to lateral rectus muscle
Conditions caused by nerve damage
Paralysis of lateral rectus limits lateral movement of eye; diplopia (double vision)
Cranial Nerves
CN VII FACIAL NERVE (fa¯ ́sha˘l; fascialis = of the face)
Temporal branch
Geniculate ganglion
Lacrimal gland
Greater petrosal nerve
Pons
Facial nerve (CN VII)
Pterygopalatine ganglion
Zygomatic branch
Posterior auricular branch
Stylomastoid foramen
Chorda tympani nerve
(traveling to mandibular
branch of CN V)
Parotid gland
Buccal branch
Branch of lingual nerve of CN V
Submandibular ganglion
Mandibular branch
Cervical branch
Description
Sensory function
Innervates muscles of facial expression, lacrimal (tear) gland, and most salivary glands; conducts taste sensations
from anterior two-thirds of tongue
Taste from anterior two-thirds of tongue
Somatic motor function
The five major motor branches (temporal, zygomatic, buccal, mandibular, and cervical) innervate the muscles of
facial expression, the posterior belly of the digastric muscle, and the stylohyoid and stapedius muscles
Parasympathetic motor function
Increases secretions of the lacrimal gland of the eye as well as the submandibular and sublingual salivary glands
Origin
Pathway
Conditions caused by nerve damage
Nuclei within the pons
Sensory axons travel from the tongue via the chorda tympani branch of the facial nerve through a tiny foramen to
enter the skull, and axons synapse at the geniculate ganglion of the facial nerve. Somatic motor axons leave the
pons and enter the temporal bone through the internal acoustic meatus, project through temporal bone, and emerge
through stylomastoid foramen to supply the musculature. Parasympathetic motor axons leave the pons, enter the
internal acoustic meatus, leave with either the greater petrosal nerve or chorda tympani nerve, and travel to an
autonomic ganglion before innervating their respective glands
Decreased tearing (dry eye) and decreased salivation (dry mouth); loss of taste sensation to anterior two-thirds of
tongue and/or facial nerve palsy (sometimes called Bell palsy) characterized by paralyzed facial muscles, lack of
obicularis oculi contraction, sagging at corner of mouth
Cranial Nerves
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Table 15.8
Cranial Nerves
CN VIII VESTIBULOCOCHLEAR NERVE (ves-tib ́u¯-lo¯ -kok ́le¯ -a˘ r; relating to the vestibule and cochlea of the ear)
Vestibular branch
Internal acoustic meatus
Vestibulocochlear
nerve (CN VIII)
Cochlear
branch
Semicircular
canals
Tympanic
cavity
(middle ear)
Tympanic
membrane
(eardrum)
Cochlea
Description
Pons
Medulla
oblongata
Conducts equilibrium and auditory sensations to brain; formerly called the auditory nerve or acoustic nerve
Sensory function
Vestibular branch conducts impulses for equilibrium while cochlear branch conducts impulses for hearing
Origin
Vestibular branch: Hair cells in the vestibule of the inner ear
Cochlear branch: Cochlea of the inner ear
Pathway
Conditions caused by nerve damage
Sensory cell bodies of the vestibular branch are located in the vestibular ganglion, while sensory cell bodies of the
cochlear branch are located in the spiral ganglion near the cochlea. The vestibular and cochlear branches merge,
and together enter cranial cavity through internal acoustic meatus and travel to junction of the pons and the
medulla oblongata
Lesions in vestibular branch produce loss of balance, nausea, vomiting, and dizziness; lesions in cochlear branch
result in deafness (loss of hearing)
Cranial Nerves
CN IX GLOSSOPHARYNGEAL NERVE (glos ́o¯ -fa˘ -rin ́je¯ -a˘ l; glossa = tongue)
Superior ganglion
Otic ganglion
To parotid gland
Inferior ganglion
Glossopharyngeal
nerve (CN IX)
To stylopharyngeus
muscle
To posterior 1/3
of tongue for taste
and general sensation
To carotid body
and carotid sinus
Description
Receives taste and touch sensations from posterior tongue, innervates one pharynx muscle and the parotid
salivarygland
Sensory function
General sensation and taste to posterior one-third of tongue; chemoreceptor axons to carotid bodies (structures on
the carotid arteries that detect and monitor O2 and CO2 levels in the blood)
Somatic motor function
Increases secretion of parotid salivary gland
Parasympathetic motor function
Innervates stylopharyngeus (pharynx muscle)
Origin
Sensory axons originate on taste buds and mucosa of posterior one-third of tongue, as well as the carotid bodies.
Motor axons originate in nuclei in the medulla oblongata
Pathway
Sensory axons travel from posterior one-third of tongue and carotid bodies along nerve through the inferior or
superior ganglion into the jugular foramen, and travel to pons. Somatic motor axons leave cranium via jugular
foramen and travel to stylopharyngeus. Parasympathetic motor axons travel to otic ganglion and then to parotid
gland
Conditions caused by nerve damage
Reduced salivary secretion (dry mouth); loss of taste sensations to posterior one-third of tongue
Cranial Nerves
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Table 15.8
Cranial Nerves
CN X VAGUS NERVE (va¯ ́gu˘ s; wandering)
Superior ganglion
Inferior ganglion
Pharyngeal branch
Superior laryngeal nerve
Internal laryngeal nerve
External laryngeal nerve
Right vagus nerve (CNX)
Left vagus nerve (CNX)
Right recurrent
Laryngeal branch
Left recurrent
laryngeal branch
Cardiac branch
Lung
Pulmonary plexus
Heart
Anterior vagal trunk
(formed from left vagus)
Kidney
Spleen
Liver
Stomach
Pancreas
Small intestine
Ascending
colon
Appendix
Description
Sensory function
Somatic motor function
Parasympathetic motor function
Origin
Innervates structures in the head and neck and in the thoracic and abdominal cavities
Visceral sensory information from pharynx, larynx, heart, lungs, and most abdominal organs. General sensory
information from external acoustic meatus, eardrum, and pharynx
Innervates most pharynx muscles and larynx muscles
Innervates visceral smooth muscle, cardiac muscle, and glands of heart, lungs, pharynx, larynx, trachea, and most
abdominal organs
Motor nuclei in medulla oblongata
Pathway
Leaves cranium via jugular foramen before traveling and branching extensively in neck, thorax, and abdomen;
sensory neuron cell bodies are located in the superior and inferior ganglia associated with the nerve
Conditions caused b\y nerve damage
Paralysis leads to a variety of larynx problems, including hoarseness, monotone voice, or complete loss of voice.
Other lesions may cause diffi culty in swallowing or impaired gastrointestinal system mobility
Cranial Nerves
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Table 15.8
Cranial Nerves
CN XI ACCESSORY NERVE (ak-ses ́o¯-re¯; accedo = to move toward)
Pons
Spinal root
Cranial root
Foramen magnum
Medulla oblongata
Cervical region of
spinalcord(C1–C5)
Jugular foramen
Vagus nerve (CNX)
Cranial root diverges
and joins vagus nerve
Accessory nerve (CNXI)
Sternocleidomastoid muscle
Trapezius muscle
Description
Innervates trapezius, sternocleidomastoid, and some pharynx muscles; formerly called the “spinal accessory nerve”
Somatic motor function
Cranial root: Travels with CN X fi bers to pharynx
Spinal root: Innervates trapezius and sternocleidomastoid
Origin
Cranial root: Motor nuclei in medulla oblongata
Spinal root: Motor nuclei in spinal cord
Pathway
Conditions caused by nerve damage
Spinal root travels superiorly to enter skull through foramen magnum; there, cranial and spinal roots merge and
leave the skull via jugular foramen. Once outside the skull, cranial root splits to travel with CN X (vagus) to
innervate pharynx muscles, and spinal root travels to sternocleidomastoid and trapezius
Paralysis of trapezius and sternocleidomastoid, resulting in diffi culty in elevating shoulder (trapezius function) or
turning head to opposite site (sternocleidomastoid function)
Cranial Nerves
CN XII HYPOGLOSSAL NERVE (hı¯-po¯ -glos ́a˘l; hypo = below, glossus = tongue)
Hypoglossal
Nerve (CNXII)
C1
C2
C3
Ansa cervicalisto
Infrahyoid muscles
(cervical nerves
Running with
hypoglossal)
To tongue muscles
To geniohyoid muscle
Description
Innervates intrinsic and extrinsic tongue muscles; name means “under the tongue”
Somatic motor function
Innervates intrinsic and extrinsic tongue muscles
Origin
Hypoglossal nucleus in medulla oblongata
Pathway
Leaves cranium via hypoglossal canal; travels inferior to mandible and to inferior surface of tongue
Conditions caused by nerve damage
Swallowing and speech diffi culties due to impaired tongue movement; if a single hypoglossal nerve (either left or
right) is paralyzed, a protruded (stuck out) tongue deviates to the side of the damaged nerve