The Peripheral Nervous System and Reﬂex Activity
Motor branch to muscles of
facial expression—see part (b)
(a) Parasympathetic efferents and sensory afferents
(b) Motor branches to muscles of facial expression and scalp
muscles (see pp. 329–331)
VI Abducens Nerves
Origin and course:
Fibers leave inferior pons and enter orbit via
superior orbital ﬁssure to run to eye.
Primarily motor; supply somatic motor ﬁbers to lateral rectus
muscle, an extrinsic muscle of the eye. Convey proprioceptor impulses
from same muscle to brain.
Test in common with cranial nerve III (oculomotor).
In abducens nerve
paralysis, eye cannot be moved laterally. At rest, eyeball rotates
VII Facial Nerves
Origin and course:
Fibers issue from pons, just lateral to abducens nerves
(see Figure 13.6), enter temporal bone via
internal acoustic meatus
run within bone (and through inner ear cavity) before emerging through
. Nerve then courses to lateral aspect of face.
Mixed nerves that are the chief motor nerves of face. Five
major branches: temporal, zygomatic, buccal, mandibular, and cervical
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
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
ı n) and
on the trigeminal nerve (see
Convey sensory impulses from taste buds of anterior two-thirds
of tongue; cell bodies of these sensory neurons are in
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.
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.