Head and Neck
Answers
274.The answer is c.(Moore and Dalley, p 973.)The long ciliary (CN V1)
nerve carries pain information from the eye, which causes the eye to close
due to firing of the orbicular oculi, a muscle of facial expression innervated
by the zygomatic branch of the facial nerve (CN VII). Short ciliary nerves
(answers a and b),by definition, have traveled through the ciliary ganglia
(some have synapsed) and therefore are postganglionic parasympathetic
fibers, which will innervate the intraocular eye muscles for accommodation
of the iris and pupil. The infraorbital branch of CN V 2 (answers d and e),
while sensory, does not innervate the eye, but does innervate the skin and
lower eyelid, but not the cornea of the eye.
275.The answer is c.(Moore and Dalley, pp 1134–1135.)Information
from the nasal retinal field crosses the midline at the optic chiasm; thus
images from the right visual fields strike the left retinal fields of both eyes
and from the right eye cross at the optic chiasm (see figure on next page).
The images that strike the left temporal retina (from the right visual
field) of the left eye stay on the left and join the nasal retinal field of the
right eye in the left optic tract. An aneurysm in the left middle cerebral
artery, if large enough, would likely impinge on the left optic tract. A pitu-
itary tumor (answer a)would likely compress the optic chiasm leading to
a loss of the temporal visual fields in both eyes, or tunnel vision (or bitem-
poral hemianopsia). A tumor in the right orbit that compresses the right
optic nerve (answer b)would just lead to loss of vision in the right eye.
Compromise of the right optic tract (answer d)would lead to loss of left
visual fields in both eyes. An aneurysm affecting the arterial supply to the
occipital visual cortex (answer e)would be very unlikely to produce the
symptoms described.
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