Chapter 13
The Peripheral Nervous System and Reflex Activity
497
13
Superior
orbital fissure
Pons
Lateral
rectus
muscle
Abducens
nerve (VI)
Temporal
Zygomatic
Buccal
Mandibular
Cervical
Motor branch to muscles of
facial expression—see part (b)
Submandibular
gland
Sublingual gland
Submandibular
ganglion
Stylomastoid
foramen
Chorda tympani
branch (taste)
Parasympathetic
nerve fibers
Parasympathetic
nerve fibers
Lacrimal gland
Pterygopalatine
ganglion
Geniculate
ganglion
Internal
acoustic
meatus
Facial
nerve
(VII)
(a) Parasympathetic efferents and sensory afferents
(b) Motor branches to muscles of facial expression and scalp
muscles (see pp. 329–331)
VI Abducens Nerves
(ab-du
9
senz)
Origin and course:
Fibers leave inferior pons and enter orbit via
superior orbital fissure to run to eye.
Function:
Primarily motor; supply somatic motor fibers to lateral rectus
muscle, an extrinsic muscle of the eye. Convey proprioceptor impulses
from same muscle to brain.
Clinical testing:
Test in common with cranial nerve III (oculomotor).
Homeostatic Imbalance
In abducens nerve
paralysis, eye cannot be moved laterally. At rest, eyeball rotates
medially
(internal strabismus
).
VII Facial Nerves
Table 13.2
(continued)
Origin and course:
Fibers issue from pons, just lateral to abducens nerves
(see Figure 13.6), enter temporal bone via
internal acoustic meatus
, and
run within bone (and through inner ear cavity) before emerging through
stylomastoid foramen
. Nerve then courses to lateral aspect of face.
Function:
Mixed nerves that are the chief motor nerves of face. Five
major branches: temporal, zygomatic, buccal, mandibular, and cervical
(see
c
on next page).
Convey motor impulses to skeletal muscles of face (muscles
of facial expression), except for chewing muscles served by
trigeminal nerves, and transmit proprioceptor impulses from
same muscles to pons (see
b
).
Transmit parasympathetic (autonomic) motor impulses to
lacrimal (tear) glands, nasal and palatine glands, and
submandibular and sublingual salivary glands. Some of the
cell bodies of these parasympathetic motor neurons are in
pterygopalatine
(ter
0
eh-go-pal
9
ah-tˉ
ı n) and
submandibular
ganglia
on the trigeminal nerve (see
a
).
Convey sensory impulses from taste buds of anterior two-thirds
of tongue; cell bodies of these sensory neurons are in
geniculate ganglion
(see
a
).
Clinical testing:
Test anterior two-thirds of tongue for ability to taste
sweet (sugar), salty, sour (vinegar), and bitter (quinine) substances.
Check symmetry of face. Ask subject to close eyes, smile, whistle, and
so on. Assess tearing with ammonia fumes.
Homeostatic Imbalance
Bell's palsy
is
characterized by paralysis of facial muscles on affected side and
partial loss of taste sensation. May develop rapidly (often overnight).
Caused by inflamed and swollen facial nerve, possibly due to herpes
simplex 1 viral infection. Lower eyelid droops, corner of mouth sags
(making it difficult to eat or speak normally), tears drip continuously
from eye and eye cannot be completely closed (conversely, dry-eye
syndrome may occur). Treated with corticosteroids. Recovery is
complete in 70% of cases.
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