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Peripheral Nervous System & Reflex
Activity
Part B: Cranial Nerves
Prepared by Janice Meeking & W. Rose.
Figures from Marieb & Hoehn 8th, 9th ed.
Portions copyright Pearson Education
Cranial Nerves
• Twelve pairs of nerves associated with the
brain
• Most are mixed in function; two pairs are
purely sensory
• Each nerve is identified by a number
(I through XII) and a name
“On occasion, our trusty truck acts funny—very
good vehicle anyhow”
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Frontal lobe
Temporal lobe
Infundibulum
Facial
nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Filaments of
olfactory
nerve (I)
Olfactory bulb
Olfactory tract
Optic nerve
(II)
Optic chiasma
Optic tract
Oculomotor
nerve (III)
Trochlear
nerve (IV)
Trigeminal
nerve (V)
Abducens
nerve (VI)
Cerebellum
Medulla
oblongata
(a)
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Figure 13.5 (a)
Cranial nerves
I – VI
I
II
III
IV
V
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
VI Abducens
Cranial nerves
VII – XII
VII Facial
VIII Vestibulocochlear
IX
X
XI
XII
(b)
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Glossopharyngeal
Vagus
Accessory
Hypoglossal
Sensory
function
Motor
function
PS*
fibers
Yes (smell)
Yes (vision)
No
No
Yes (general
sensation)
No
No
Yes
Yes
Yes
No
No
Yes
No
No
No
Yes
No
Sensory
function
Motor
function
PS*
fibers
Yes (taste)
Yes (hearing
and balance)
Yes
Some
Yes
No
Yes (taste)
Yes (taste)
No
No
Yes
Yes
Yes
Yes
Yes
Yes
No
No
*PS = parasympathetic
Figure 13.5 (b)
I: The Olfactory Nerves
• Arise from the olfactory receptor cells of nasal
cavity
• Pass through the cribriform plate of the
ethmoid bone
• Fibers synapse in the olfactory bulbs
• Pathway terminates in the primary olfactory
cortex
• Purely sensory (olfactory) function
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
II: The Optic Nerves
• Arise from the retinas
• Pass through the optic canals, converge and
partially cross over at the optic chiasma
• Optic tracts continue to the thalamus, where
they synapse
• Optic radiation fibers run to the occipital
(visual) cortex
• Purely sensory (visual) function
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
III: The Oculomotor Nerves
• Fibers extend from the ventral midbrain
through the superior orbital fissures to the
extrinsic eye muscles
• Functions in raising the eyelid, directing the
eyeball, constricting the iris
(parasympathetic), and controlling lens shape
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
IV: The Trochlear Nerves
• Fibers from the dorsal midbrain enter the
orbits via the superior orbital fissures to
innervate the superior oblique muscle
• Primarily a motor nerve that directs the
eyeball
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
V: The Trigeminal Nerves
• Largest cranial nerves; fibers extend from pons to
face
• Three divisions
• Ophthalmic (V1) passes through the superior orbital
fissure
• Maxillary (V2) passes through the foramen rotundum
• Mandibular (V3) passes through the foramen ovale
• Convey sensory impulses from various areas of the
face (V1) and (V2), and supplies motor fibers (V3) for
mastication
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
Copyright © 2010 Pearson Education, Inc.
Table 13.2
VI: The Abducens Nerves
• Fibers from the inferior pons enter the orbits
via the superior orbital fissures
• Primarily a motor, innervating the lateral
rectus muscle
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Copyright © 2010 Pearson Education, Inc.
Table 13.2
VII: The Facial Nerves
• Fibers from the pons travel through the internal
acoustic meatuses, and emerge through the
stylomastoid foramina to the lateral aspect of the
face
• Chief motor nerves of the face with 5 major branches
• Motor functions include facial expression,
parasympathetic impulses to lacrimal and salivary
glands
• Sensory function (taste) from the anterior two-thirds
of the tongue
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
Copyright © 2010 Pearson Education, Inc.
Table 13.2
VIII: The Vestibulocochlear Nerves
• Afferent fibers from the hearing receptors
(cochlear division) and equilibrium receptors
(vestibular division) pass from the inner ear
through the internal acoustic meatuses, and
enter the brain stem at the pons-medulla
border
• Mostly sensory function; small motor
component for adjustment of sensitivity of
receptors
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
IX: The Glossopharyngeal Nerves
• Fibers from the medulla leave the skull via the
jugular foramen and run to the throat
• Motor functions: innervate part of the tongue
and pharynx for swallowing, and provide
parasympathetic fibers to the parotid salivary
glands
• Sensory functions: fibers conduct taste and
general sensory impulses from the pharynx
and posterior tongue, and impulses from
carotid chemoreceptors and baroreceptors
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
X: The Vagus Nerves
• The only cranial nerves that extend beyond the head
and neck region
• Fibers from the medulla exit the skull via the jugular
foramen
• Most motor fibers are parasympathetic fibers that
help regulate the activities of the heart, lungs, and
abdominal viscera
• Sensory fibers carry impulses from thoracic and
abdominal viscera, baroreceptors, chemoreceptors,
and taste buds of posterior tongue and pharynx
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
XI: The Accessory Nerves
• Formed from ventral rootlets from the C1–C5
region of the spinal cord (not the brain)
• Rootlets pass into the cranium via each
foramen magnum
• Accessory nerves exit the skull via the jugular
foramina to innervate the trapezius and
sternocleidomastoid muscles
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
XII: The Hypoglossal Nerves
• Fibers from the medulla exit the skull via the
hypoglossal canal
• Innervate extrinsic and intrinsic muscles of the
tongue that contribute to swallowing and
speech
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Table 13.2
Cranial Nerve Testing
http://library.med.utah.edu/neurologicexam/html/cranialnerve_normal.html
http://library.med.utah.edu/neurologicexam/html/cranialnerve_abnormal.html
Abnormal: “Cranial nerves 3, 4, and 6 versions” 1
Normal: “Vestibulo-ocular” (this tests III and VIII)
Abnormal: “Cranial Nerve 12- Motor” 3
If time allows: Abnormal: “Cranial nerves 3, 4, and 6 ductions” 2
If time allows: Normal: “Cranial Nerve 12- Motor”
1. Versions: binocular tests, part of a regular exam. Pt. 1 can’t abduct L, i.e. n.6 (L) palsy. Pt.2 limited adduct, elevate,
depress L eye, also shows ptosis-+ & dilated pupil, i.e. n.3 (L) palsy.
2. Duction (monocular) tests done iff version results abnormal. Pt can’t medially rotate either eye. Observe nystagmus
upon abduction of each eye. This & other results (not shown) suggest bilateral internuclear ophthalmoplegia, often caused
by demyelinating lesion affecting medial longitudinal fasciculus (MLF) bilaterally. Adduction defect occurs due to disruption
of MLF connections between the abducens nucleus and the lower motor neurons in the oculomotor nucleus that innervate
the medial rectus muscle.
3. Atrophy, weakness, r. deviation of tongue due to lesion of r. cranial nerve 12.
Movies from the Neurologic Exam and PediNeurologic Exam websites by Paul D. Larsen, M.D., University of Nebraska
Medical Center and Suzanne S. Stensaas, Ph.D., University of Utah School of Medicine. Additional materials for Neurologic
Exam are drawn from resources provided by Alejandro Stern, Stern Foundation, Buenos Aires, Argentina; Kathleen Digre,
M.D., University of Utah; and Daniel Jacobson, M.D., Marshfield Clinic, Wisconsin.