Chapter 13
The Peripheral Nervous System and Reflex Activity
493
13
V.
Trigeminal.
Tree (
tri
) branches spring from this, the larg-
est cranial nerve. It supplies sensory fibers to the face and motor
fibers to the chewing muscles.
VI.
Abducens.
Tis nerve controls the extrinsic eye muscle
that
abducts
the eyeball (turns it laterally).
VII.
Facial.
A large nerve that innervates muscles of
facial
ex-
pression (among other things).
VIII.
Vestibulocochlear.
Tis mostly sensory nerve for hear-
ing and balance was formerly called the
auditory nerve
.
Figure 13.6a, are brain structures and not part of cranial nerve I.
(See ±able 13.2 art for the olfactory nerve filaments.)
II.
Optic.
Because this sensory nerve of vision develops as an
outgrowth of the brain, it is really a brain tract.
III.
Oculomotor.
Te name
oculomotor
means “eye mover.”
Tis nerve supplies four of the six extrinsic muscles that move
the eyeball in the orbit.
IV.
Trochlear.
Te term
trochlear
means “pulley” and it inner-
vates an extrinsic eye muscle that loops through a pulley-shaped
ligament in the orbit.
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 chiasma
Optic nerve (II)
Optic tract
Oculomotor
nerve (III)
Trochlear
nerve (IV)
Trigeminal
nerve (V)
Abducens
nerve (VI)
Cerebellum
Medulla oblongata
(a)
Cranial nerves
I – VI
I
II
III
IV
V
VI
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
Abducens
Yes (smell)
Yes (vision)
No
No
Yes (general
sensation)
No
No
No
Yes
Yes
Yes
Yes
No
No
Yes
No
No
No
Cranial nerves
VII – XII
Sensory
function
Motor
function
PS*
fibers
Sensory
function
Motor
function
PS*
fibers
VII
VIII
IX
X
XI
XII
Facial
Vestibulocochlear
Glossopharyngeal
Vagus
Accessory
Hypoglossal
Yes (taste)
Yes (hearing
and balance)
Yes (taste)
Yes (taste)
No
No
Yes
Some
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
No
No
*PS = parasympathetic
(b)
Figure 13.6
Location and function of
cranial nerves.
(a)
Ventral view of the
human brain, showing the cranial nerves.
(b)
Summary of cranial nerves by function.
Two cranial nerves (I and II) have sensory
function only, no motor function. Four nerves
(III, VII, IX, and X) carry parasympathetic
fibers that serve visceral muscles and glands.
All cranial nerves that innervate muscles also
carry afferent fibers from proprioceptors in
the muscles served. Only sensory functions
other than proprioception are indicated.
(Text continues on p. 500.)
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