437.The answer is b.(Moore and Dalley, pp 228–229.)A dark mass
within the scrotum would most likely be one of two things: varicocele or
indirect inguinal hernia. Varicoceles are a stasis of blood within the
pampiniform plexus and occur most frequently on the left side because the
testicular vein on the left drains into the higher pressure left renal vein,
whereas the right testicular vein drains into the inferior vena cava. The
presence of a varicocele is associated with reduced fertility. A femoral her-
nia(answers c and d)wouldnotend up in the scrotum, rather within the
thigh. Cryptorchidism (answer a),that is an undescended testicle, on the
right side does notfit the physical examination findings. The right side is
normal [thus not(answer e)].
438.The answer is b.(Moore and Dalley, pp 399, 425, 432.)Postsynaptic
sympathetic neurons destined for the skin lie in the ganglia of the sympa-
thetic chain. Although the preganglionic fibers arise between T1 and L2,
each of the sacral ganglia has a gray ramus that brings postganglionic fibers
to the associated spinal nerve. These sympathetic neurons mediate sweat-
ing (sudomotor), vasoconstriction (vasomotor), and piloerection (pilomotor)
in dermatomes S1–S5. Male ejaculation is practically mediated by skeletal
muscle (contraction of the bulbospongiosus muscle innervated by superfi-
cial perineal nerves, branches of the pudendal nerve.) Ejaculation also
requires sympathetic discharge to keep the internal urethral sphincter
closed, preventing so called retroejaculation into the bladder. Emission
(rapid contraction of the vas deferens) is mainly mediated by sympathetic,
but mainly by lumbar splanchnic nerves, thereby bypassing the sympa-
thetic chain ganglia. Erection in both male and female (answers c and d)
is mainly mediated by parasympathetic nerves. Bladder contraction
(answer a)is also mainly controlled by parasympathetic nerves.
439.The answer is e.(Moore and Dalley, p 449.) The bulbospongiosus
muscle is innervated by the pudendal nerve (S2–S4) and its contraction
helps to keep blood within the shaft of the penis. Contraction of the inter-
nal urethral sphincter is under control of the sympathetic nervous system
[thus not (answer a)]. Concomitant with dilation of the helicine arteries
under parasympathetic innervation [thus not (answers b and c)], which
allows increased blood to flow into the cavernous spaces, contraction of the
bulbospongiosus and ischiocavernosus muscles at the base of the cavernous
554 Anatomy, Histology, and Cell Biology