bleeding inside the skull. (Older brains tend to shrink due to slow neu-
ronal loss leaving more space for movement within the skull.) Subdural
hematomas are often due to a tearing of cerebral veins as they enter the
superior sagittal sinus. As the vein tears it often bleeds into to a potential
space inside the dura mater, but outside the fluid impervious outer layer of
the arachnoid mater. These are veins that bleed into this potential space, so
bleeding is often slow to develop. Subdural hematomas are usually treated
by drilling a small hole in the skull bones over the center of the hematoma
and the blood clot is removed. Normally the initial tear of the vein repairs
itself with time. Epidural hematomas (answer a)are rare if there are no
skull fractures. A pituitary tumor (answer c)might affect vision, but nor-
mally does notcause papilledema. Grave’s disease (answer d)may produce
exophthalmus and would be present before the fall. Trigeminal neuralgias
(answer e)are rarely produced by falls.
286.The answer is c.(Moore and Dalley, pp 919–920, 967. Waxman, pp
66–67, 203.)A lesion of the spinal canal that compresses the ventral com-
missure (syringomyelia) would interrupt ascending fibers crossing there,
but would not interfere with already crossed fibers ascending in the lateral
spinothalamic tracts. Pain and temperature sensation above and below the
level of the cord lesion would be preserved. The cell bodies of first-order
afferent (sensory) neurons are located in the dorsal root ganglia. Their cen-
tral processes enter the spinal cord and ascend one segment before synaps-
ing with a second-order neuron in the dorsal horn. The central processes of
second-order neurons cross in the ventral white commissure to the oppo-
site side of the cord and ascend in the lateral spinothalamic tract to the ven-
tral posterior lateral nucleus of the thalamus where they synapse with
third-order neurons, which relay the message to cortical neurons of the
postcentral gyrus of the parietal lobe. Lesions occurring unilaterally in a
peripheral nerve would result in an ipsilateral deficit, whereas lesions in a
crossed ascending pathway, in the thalamus, or in the cortex would result
in contralateral deficits.
287.The answer is d.(Moore and Dalley, p 990. Sadler, pp 273–278.)The
lateral nasal process forms the alar region of the nose. Normally the maxil-
lary process moves medially and fuses with the medial nasal process at the
philtrum on both sides of the upper lip. The fact that the cleft involves both
the lip and bony primary palate suggests failure of the maxillary process
440 Anatomy, Histology, and Cell Biology