Chapter 14
Transcript of Chapter 14
Copyright © John Wiley & Sons, Inc. All rights reserved.
Chapter 14
The Brain and Cranial
Nerves
Lecture slides prepared by Curtis DeFriez, Weber State University
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Human Brain
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Human Brain The human brain, compared to all other animals’
brains, is marked by the highest ratio of brain to
body size - thought to directly correlate with our
higher level of intelligence.
Most of the expansion is manifest in man’s
large cerebral cortex. Especially expanded are
the frontal lobes which are associated with
higher (executive) functions
such as self-control, planning,
reasoning, and abstract thought.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Brain Development During the first 3 weeks of gestation, the human
embryo's neural tube flexes as it grows, forming
the three primary brain vesicles colloquially
called
the forebrain, midbrain, and
hindbrain. The 1st and 3rd
vesicles further divide forming
5 secondary brain vesicles in a
process called encephalization.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Brain Development The major parts of the adult brain are directly
derived from the 2o brain vesicles: From the
crescent-shaped cerebral hemispheres of the
telencephalon to the inferiorly placed brain stem
formed from the
metencephalon and
myelencephalon
Copyright © John Wiley & Sons, Inc. All rights reserved.
Brain Development The brain grows at an amazing rate during
development; at times, as many as 50,000
neurons are added each second!
At birth, the neonatal brain looks very much like
that of an adult and almost all
the neurons the brain
will ever have are
already present.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Brain Organization The brain stem is the continuation of the
spinal cord and consists of the medulla
oblongata, pons and midbrain.
The cerebellum is the second largest part of
the brain.
The diencephalon gives rise to the thalamus
& hypothalamus.
The cerebrum is the newest (evolutionarily)
and largest part of the brain as a whole.
It is in the cerebral cortex that perception,
thought, imagination, judgment, and decision
making occur.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Brain Organization The major parts of the adult brain are shown here
Copyright © John Wiley & Sons, Inc. All rights reserved.
Protective Coverings The cranial meninges are continuous with
the spinal meninges and mirror their structure
and function – they also bear the
same names: a tough outer dura mater a spidery arachnoid
mater and a thin,
delicate pia
mater
Copyright © John Wiley & Sons, Inc. All rights reserved.
Protective Coverings The cranial dura mater, however, has two
layers – an external periosteal layer and an
internal meningeal layer; the spinal dura mater
has only one.
In the brain, extensions of the dura mater
form hard, non-compliant membranes that
divide the intracranial vault in various ways:.
The 3 important dural extensions are the falx
cerebri, the falx cerebelli, and the
tentorium cerebelli.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Protective Coverings The falx cerebri is a strong sickle-shaped fold
of dura mater which descends vertically in the
longitudinal fissure and separates the two
cerebral hemispheres.
The falx cerebelli is a
small triangular
process that separates
the two cerebellar
hemispheres.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Protective Coverings Clinically, the tentorium cerebelli is
important because brain tumors are often
characterized as supratentorial (above the
tentorium) and infratentorial (below the
tentorium). Most childhood tumors are
infratentorial, while most adult tumors are
supratentorial.
Since the tentorium is a hard structure, if
there is any brain swelling the brain can get
partly pushed down and herniate through the
tentorium, which becomes a life-threatening
event.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The brain represents only 2 percent of total body
weight, but receives about 20% of the body’s
blood supply and consumes 20% of the O2 and
glucose (even when resting).
Anteriorly, the internal carotid arteries
supply blood to the brain; the posterior blood
supply is
via the vertebral arteries.
The internal
jugular veins are
the venous return
Brain Blood Flow
Copyright © John Wiley & Sons, Inc. All rights reserved.
The vascular endothelium around brain
capillaries differs from most other organs of the
body in that it forms tight junctions with the
end-feet of nearby astrocytes.
As a result of this unusual architecture, a blood
brain barrier (BBB) is formed
that serves to isolate the
parenchyma of the brain
from many substances in
the blood that would
normally be able to gain access.
Encyclopedia of Life Sciences, © Wiley
Brain Blood Flow
Copyright © John Wiley & Sons, Inc. All rights reserved.
Brain Blood Flow The BBB protects the brain from some harmful
substances (like bacteria), but at a cost:
For one thing, certain molecules needed to
meet metabolic needs (such as glucose) must
be actively transported across the barrier
using specific transport proteins and energy.
Another aspect of the BBB is that if a brain
infection were to develop, antibiotics (and
many other drugs) have difficulty crossing into
the brain tissues and reaching therapeutic
levels.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Brain Blood Flow The BBB can be used advantageously in certain
pharmacological situations. For example, it is well
known that certain older antihistamine drugs readily
cross the BBB and cause sedation. This makes these
drugs not very good antihistamines, but very helpful in
cough and cold medications to induce sleep (NyQuil).
Drugs companies have devoted enormous resources
to the development of newer 2nd and 3rd generation
antihistamines that do not cross the BBB, and don’t
(usually) cause somnolence – they also charge you
accordingly.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cerebral spinal fluid is a clear fluid that
circulates through the internal cavities in the
brain (called brain ventricles) and spinal cord
(the central canal) and also flows over and
around the brain and cord in the subarachnoid
space. In essence, the brain "floats" in it.
CSF absorbs shock and protects the brain and
the cord.
• It also helps transport nutrients and wastes
between blood and nervous tissues.
Production and Flow of CSF
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Irrigation System of the fluid filled brain showing the
circulating CSF.
Production and Flow of CSF
Copyright © John Wiley & Sons, Inc. All rights reserved.
Production and Flow of CSF The majority of CSF production - 80 to 150 mL at
any given time in an adult - comes from
ependymal cells in the choroid plexuses
(networks of blood capillaries that line the
ventricles).
The pathway CSF follows from the internal
ventricles to the SAS is given in the following
sequence:
• lateral ventricles interventricular foramina
third ventricle cerebral aqueduct fourth
ventricle median aperture (of Magendie )
and the lateral apertures (of Luschka ) SAS
Copyright © John Wiley & Sons, Inc. All rights reserved.
Production and Flow of CSF The choroid plexuses can be seen in this
superior view of a transverse section through
the brain:
Copyright © John Wiley & Sons, Inc. All rights reserved.
Once in the SAS, CSF flows continuously between the
pia mater covering the brain and the arachnoid that
is tightly
adhered to the outer dura.
Pressure remains
constant in the head
because the rate of
fluid reabsorption
closely matches fluid
formation at approx.
20 mL/h.
Production and Flow of CSF
Copyright © John Wiley & Sons, Inc. All rights reserved.
__ _________ __________ ____ ____ ___ _____
_______ ___ _________ _____ ______ ____
___________ ____ ______ ____ ___ _____ _______
_ ____ _______ ___
_________ _____ ___
____ __________
____ ___ ________
________ _____ _______ __
_________ _____ __ ______
__ _________ ___________
CSF is gradually reabsorbed back into the blood
through the arachnoid villi (finger-like
projections that extend into the dural sinuses).
In this graphic, the
arachnoid villi are
seen projecting
into the superior
sagittal sinus. A cluster of
arachnoid villi is called
an arachnoid granulation.
Production and Flow of CSF
Copyright © John Wiley & Sons, Inc. All rights reserved.
Failure of CSF to form and drain normally results
in a buildup of pressure called hydrocephalus.
Hydrocephalus occurs with congenital
abnormalities, head injury, meningitis,
and episodes of
bleeding into
the brain.
_________ ___ ___ __ Production and Flow of CSF
Copyright © John Wiley & Sons, Inc. All rights reserved.
Parts of the Brain
Copyright © John Wiley & Sons, Inc. All rights reserved.
The brain stem is superior to, but continuous
with, the spinal cord. Developmentally, it does
not represent a single structure, but rather a
group
of anatomical components
considered collectively.
It is made up of
the midbrain, pons,
and medulla oblongata.
The Brain Stem
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Medulla Oblongata
Copyright © John Wiley & Sons, Inc. All rights reserved.
It has two external bulges called the pyramids
formed by the largest motor tracts in the body.
Axons from the left pyramid cross over to the
right and axons on the right cross over to
the left (decussation of
pyramids) – so that the left
hemisphere of the brain
controls the right
side muscles, while the right
hemisphere controls the left side.
The Medulla Oblongata
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Medulla Oblongata Vital functional centers regulated by the
medulla include:
The cardiovascular center – controls the
rate and force of heartbeat, and the diameter
of blood vessels
The respiratory rhythmicity center –
controls the rate and rhythm of breathing
The vomiting, coughing, and sneezing
centers
The nuclei associated with 5 of the 12 cranial
nerves originates in the medulla (CN VIII – XII).
A portion of the 4th ventricle extends to the
medulla.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Medulla Oblongata
Three cranial nerves emerge from the
medulla.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Pons The pons lies directly above the medulla and
anterior to the cerebellum (2.5 cm). It acts as a
bridge connecting the spinal cord with the brain
and
parts of the brain with
each other.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Pons Together with the medulla, areas in the pons
help control breathing (inhalation and
exhalation).
The pontine respiratory group is normally
inactive during quiet breathing. This group of
neurons acts like an “off-switch” to terminate
medullary inspiratory activity.
Early termination of inspiration leads to an
increase in the rate of breathing (which is why
this center was formerly know as the
“pneumotaxic center” - taxic meaning fast).
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Pons
CN V exits the pons, while 3 others
come from the medullary pontine
angle.
The pons contains the nuclei associated with 4
pairs of cranial nerves: V - VIII
Cranial nerve V
emerges directly
from the pons.
VI, VII, and VIII
emerge from the
space between
the pons and
the medulla.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Midbrain The midbrain extends from the pons to the
diencephalon.
The cerebral aqueduct passes through the
midbrain connecting the 3rd ventricle
above with the 4th
ventricles below
(both locations
of CSF formation
and circulation.)
Copyright © John Wiley & Sons, Inc. All rights reserved.
On the anterior part of the midbrain are found
the “little feet” of the cerebral peduncles.
The peduncles contain axons of the
corticospinal, corticobulbar, and
corticopontine tracts which conduct nerve
impulses from motor areas in the cerebral
cortex to the spinal
cord, medulla,
and pons,
respectively.
The Midbrain
Copyright © John Wiley & Sons, Inc. All rights reserved.
On the posterior part of the midbrain are four
rounded elevations known as the superior
and inferior colliculi which serve as reflex
centers for certain visual and auditory
reflexes,
and also the
startle reflex.
It is the origin of
cranial nerves III
and IV.
The Midbrain
Copyright © John Wiley & Sons, Inc. All rights reserved.
The midbrain contains several other nuclei, including
the darkly pigmented substantia nigra. Neurons
that release dopamine, extending from the substantia
nigra, help control subconscious muscle activities;
loss of these neurons is associated with Parkinson
disease.
The red nucleus
helps control
voluntary movements
of the limbs.
The Midbrain
Copyright © John Wiley & Sons, Inc. All rights reserved.
In addition to the well-defined nuclei already
described, much of the brain stem consists of a
netlike arrangement of neuronal cell bodies and
small bundles of myelinated axons known as the
reticular formation.
The ascending portion of this network is called
the reticular activating
system (RAS), and
consists of sensory
axons that project to
the cerebral cortex.
The Reticular Formation
Copyright © John Wiley & Sons, Inc. All rights reserved.
The RAS functions to maintain
consciousness, a state of wakefulness in which
an individual is fully alert, aware, and oriented.
Inactivation of the RAS produces sleep, a state
of partial consciousness from which an individual
can be aroused.
It also prevents sensory
overload by filtering
out insignificant
information.
The Reticular Formation
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebellum The cerebellum, or “little brain”, is the second
largest part of the brain and lies inferior to the
cerebrum and posterior to the brain stem.
It is separated from
the cerebrum by
the transverse
fissure (in which
the falx cerebelli
is located).
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebellum The cerebellum’s central constricted area is the
vermis and the lateral “wings” or lobes are the
cerebellar hemispheres . The cerebellum compares intended
movements with what is happening with
skeletal muscles, and regulates posture,
equilibrium, and balance.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Diencephalon The diencephalon is located near the midline of
the brain, above the midbrain. Like the cerebral
cortex, the diencephalon develops from the
forebrain vesicle (the prosencephalon) - yet it is
more primitive than the cerebral cortex, and lies
underneath it.
The diencephalon surrounds
the 3rd ventricle and
contains the thalamic
structures.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Diencephalon The thalamus functions as a relay station for all
sensory impulses to the cerebral cortex (except
smell, which belong to the hypothalamus). Pain,
temp, touch, and pressure are all relayed to the
thalamus en route to the higher centers of the
cerebral cortex.
While not precisely localized here (that occurs in
the cerebral cortex), all of these peripheral
sensations are processed in the thalamus in
conjunction with their attendant memories and
the emotions they evoke.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The epithalamus is superior and posterior to
the thalamus.
It consists of the pineal gland (secretes
melatonin) and habenular nuclei (emotional
responses to odors).
More melatonin is
secreted in darkness
than light, and it is
thought to promote
sleepiness and help
regulate our
biological clocks.
thalamusepithalamus
The Diencephalon
Copyright © John Wiley & Sons, Inc. All rights reserved.
The hypothalamus controls many homeostatic
functions:
It controls the Autonomic Nervous System (ANS).
It coordinates between NS and endocrine systems.
It controls body temperature (measured by blood
flowing through it).
It regulates hunger/thirst
and feelings of satiety.
It assists with the internal
circadian clock by
regulating biological activity.
thalamus
hypothalamus
The Diencephalon
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebrum The cerebral cortex is the “seat of our
intelligence”– it’s because of neurons in the
cortex that we are able to read, write, speak,
remember, and plan our life.
The cerebrum consists of an outer cerebral
cortex, an internal region of cerebral
white matter, and gray
matter nuclei deep within
the white matter.
Copyright © John Wiley & Sons, Inc. All rights reserved.
During embryonic development, the grey matter
of the brain develops faster than the white
matter - the cortical region rolls and folds on
itself. Convolutions and grooves are created in
the cortex during this growth process.
The folds are called gyri, the deepest of which
are known as fissures; the
shallower grooves between
folds are termed sulci.
The Cerebrum
Copyright © John Wiley & Sons, Inc. All rights reserved.
The prominent longitudinal fissure separates
the cerebrum into right and left cerebral
hemispheres. The central sulcus further
divides the
anterior frontal
lobe from the
more posteriorly
situated parietal lobe.
Note the precentral gyrus
and postcentral gyrus of
those two lobes.
The Cerebrum
Copyright © John Wiley & Sons, Inc. All rights reserved.
The precentral gyrus - located immediately
anterior to the central sulcus in the anterior
lobe - contains the primary motor area of the
cerebral cortex. Another major gyrus, the
postcentral gyrus, which is located
immediately posterior to the central sulcus in
the parietal lobe, contains the primary
somatosensory area of the cerebral cortex.
The parieto-occipital sulcus separates the
parietal lobe from the posterior-most
occipital lobe.
The Cerebrum
Copyright © John Wiley & Sons, Inc. All rights reserved.
The lateral cerebral sulcus (fissure) separates
the frontal lobe from two laterally placed
temporal lobes, hanging like ear muffs off the
sides. A fifth part of the cerebrum, the insula,
cannot be seen at the surface of the brain
because it lies within the lateral
cerebral sulcus, deep to
the parietal, frontal,
and temporal
lobes.
The Cerebrum
Copyright © John Wiley & Sons, Inc. All rights reserved.
frontalparietal
temporaloccipital
The lobes of the cerebrum correspond to the
bones of the braincase which bear the same
names.
The Cerebrum
frontal
occipital
parietal
temporal
frontalparietal
temporaloccipital
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebrum Brodmann’s areas are numbered regions of
cortex that have been “mapped” to specific
cognitive functions.
Sensory areas of cerebral cortex are
involved in perception of sensory
information.
Motor areas control execution of voluntary
movements.
Association areas deal with more complex
integrative functions such as memory,
personality traits, and intelligence.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebrum
Brodmann’s areas: Numbered Regions of Cortical tissue.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebrum The primary somatosensory area (areas 1, 2, and
3 – located in the postcentral gyrus of each parietal
lobe) receives nerve impulses for, and consciously
perceives the somatic sensations of touch, pressure,
vibration, itch, tickle, temperature (coldness and
warmth), pain, and proprioception (joint and muscle
position).
Each point within the area “maps” impulses from
a specific part of the body (depending on the
number of receptors present there rather than on
the size of the body part).
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebrum For example, a larger region of the
somatosensory area receives impulses from the
lips and fingertips than from the thorax or hip.
This distorted somatic sensory
map of the body is known as the
sensory homunculus (little man).
This allows us to pinpoint
(feel exactly) where somatic
sensations originate.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebrum The primary motor area (area 4 – located in
the precentral gyrus of the frontal lobe) controls
voluntary contractions of specific
muscles or groups of muscles.
The motor cortex also has a
homunculus map, with
more cortical area devoted
to muscles involved in
skilled, complex, or
delicate movement.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebrum The 1o visual area is located at the posterior
tip of the occipital lobe mainly on the medial
surface
The 1o gustatory area is located just inferior
to the 1o somatosensory area
The 1o auditory area is
in the superior part of the
temporal lobe
The 1o olfactory area is in
the inferomedial temporal lobe
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebrum The cerebral white matter consists primarily
of myelinated axons in three types of tracts.
Association tracts contain axons that
conduct nerve impulses between gyri in the
same hemisphere.
Commissural tracts conduct nerve
impulses between corresponding gyri from
one hemisphere to another.
Projection tracts convey impulses to lower
parts of the CNS (thalamus, brain stem, or
spinal cord) or visa versa.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The corpus callosum is one of the three
important groups of commissural tracts (the
other two being the anterior and posterior
commissures) – it is a thick band of axons that
connects corresponding areas of the two
hemispheres.
Through the corpus callosum, the left motor
cortex (which controls the right
body) is linked to
the right motor
cortex (which
controls the left body).
The Cerebrum
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebrum The outer surfaces of the gyri are not the only
areas of gray matter in the cerebrum. Recall
that the telencephalon consists of the cortex,
and also the basal nuclei.
The basal nuclei are conspicuous centers of
cell bodies deep in the cortex. The 3 basal
nuclei help initiate and terminate
movements, suppress unwanted movements,
and regulate muscle tone.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Cerebrum The basal nuclei also control subconscious
contractions of skeletal muscles. Examples
include automatic arm swings while walking and
true laughter in response to a joke.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Limbic System Encircling the upper part of the brain stem and
the corpus callosum is a ring of structures on
the inner border of the cerebrum
and floor of the
diencephalon that
constitutes the
limbic system.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Limbic System The limbic system does not represent any one
part of the brain – it is more a functional
system composed of parts of the cerebral
cortex, diencephalon, and midbrain.
The limbic system is sometimes called the
“emotional brain” because it plays a primary
role in promoting a range of emotions, including
pleasure, pain, docility, affection, fear, and
anger.
Together with parts of the cerebrum, the
limbic system also functions in memory.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Hemispheric Lateralization Although the brain is almost symmetrical on its
right and left sides and shares performance of
many functions, there are subtle anatomical
and physiological differences between the two
hemispheres.
Each hemisphere specializes in performing
certain unique functions, a feature known as
hemispheric lateralization. Despite some
dramatic differences, there is considerable
variation from one person to another. Also,
lateralization seems less pronounced in
females.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Hemispheric Lateralization In most people, the left hemisphere is more
important for reasoning, numerical and
scientific skills, spoken and written language,
and the ability to use and understand sign
language.
Conversely, the right hemisphere is more
specialized for musical and artistic awareness;
spatial and pattern perception; recognition of
faces and emotional content of language;
discrimination of different smells; and
generating mental images of sight, sound,
touch, and taste.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Brain Waves The billions of communicating brain neurons
constantly generate detectable signals
called brain waves. Those we can more
easily measure are generated by neurons
close to the brain surface, mainly neurons in
the cerebral cortex.
Electrodes placed on the
forehead and scalp can be
used to make a record called
an electroencephalogram.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Brain Waves Summing waves of different frequency produces
some characteristic, and diagnostic patterns.
Alpha (10–12 Hz (cycles/sec) waves are
present when awake but disappear during
sleep.
Beta (14–30 Hz) waves are present with
sensory input and mental activity when the
nervous system is active.
Theta (4–7 Hz) waves indicate emotional
stress or a brain disorder.
Delta (1–5 Hz) waves appear only during sleep
in adults but indicate brain damage in an
awake adult.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Brain Waves Electroencephalograms are useful both in
studying normal brain functions, such as
changes that occur during sleep, and in
diagnosing a variety of brain disorders, such as
epilepsy, tumors, trauma, hematomas,
metabolic abnormalities, sites of trauma, and
degenerative diseases.
The EEG is also utilized to determine if “life” is
present, that is, to establish or confirm that
brain death has occurred.
Copyright © John Wiley & Sons, Inc. All rights reserved.
The Twelve Cranial Nerves
Cranial Nerves
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves
Spinal and cranial nerves are compared in this
table.
Spinal Cranial
DesignationC1-8, T1-12, L1-5, S1-5,
Co1
Roman Numerals
I – XII
Number 31 pairs 12 pairs
Origin Spinal cord Brain
Number of
roots
2 - a dorsal and a ventral
rootSingle root
Contents MixedMost mixed; some
sensory only
Target Limbs/TrunkAll in the Head/Neck
(vagus n leaves)
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves
This is a picture of a masterful dissection, showing the cranial nerves in-situ (as they are “in place”).
The major functions of the 12 pairs of cranial
nerves are detailed in the
following
slides.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves
CN I is the
olfactory nerve
(sense of
smell).
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves
CN II is the optic
nerve (sense of
sight).
Copyright © John Wiley & Sons, Inc. All rights reserved.
CN III, IV, and VI innervate the extraocular
muscles that allow us to move our eyes.
CN III also supplies motor
input to our eyelid
muscles and
facilitates
pupillary
constriction.
Cranial Nerves
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN V is the trigeminal nerve (the major
sensory nerve of the face).
It has three large
branches, each of
which supplies an
area of the face:
• ophthalmic
• maxillary
• mandibular
Copyright © John Wiley & Sons, Inc. All rights reserved.
CN VII is the facial nerve. It has 5 large somatic
branches which innervate the muscle of
facial expression. It also carries some
taste sensations
(anterior 2/3 of tongue).
Paralysis of
CN VII is called
Bell’s Palsy and leads
to loss of ability to close
the eyes and impairment of
taste and salivation.
Cranial Nerves
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN VIII is the vestibulocochlear nerve. From
the inner ear, the vestibular component carries
information on balance, while the cochlear
component enables hearing.
Damage of CN VIII causes vertigo, ringing in
the ears, and/or deafness.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN IX is the glossopharyngeal nerve. This
nerve carries some taste sensations as well as
ANS impulses to salivary glands and the
mechanoreceptors of the carotid body and
carotid sinus (senses changes in BP).
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves
CN X is the
vagus nerve
(“the
wanderer”),
which carries
most of the
parasympathetic
motor efferents
to the organs of
the thorax and
abdomen.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN XI is the spinal accessory nerve. This nerve
supplies somatic motor innervation to the
Trapezius and Sternocleidomastoid muscles.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Cranial Nerves CN XII is the glossopharyngeal nerve. This is a
very large nerve (a lot of resources) to be
devoted solely to the tongue – it takes a lot
more coordination than you might guess to
chew, talk, and swallow without injuring our
tongue.
Copyright © John Wiley & Sons, Inc. All rights reserved.
End of Chapter 14Copyright 2012 John Wiley & Sons, Inc. All rights
reserved. Reproduction or translation of this work
beyond that permitted in section 117 of the 1976
United States Copyright Act without express
permission of the copyright owner is unlawful.
Request for further information should be addressed
to the Permission Department, John Wiley & Sons, Inc.
The purchaser may make back-up copies for his/her
own use only and not for distribution or resale. The
Publisher assumes no responsibility for errors,
omissions, or damages caused by the use of these
programs or from the use of the information herein.