Extremities and Spine
Answers
451.The answer is d.(Sadler, p 77.). Somatic lateral plate mesoderm gives
rise to the connective tissue, cartilage, and bones of the appendages, including
the shoulder and pelvis. The muscles of the appendages, however, originate
from somitic mesoderm [(answer e)myotome]. Neural crest cells (answer b)
contribute to the connective tissue of the head but notthe appendages. Axial
mesoderm(answer c)forms the notochord, whereas splanchnic lateral plate
mesoderm(answer a)forms the smooth muscle and connective tissue associ-
ated with the viscera.
452.The answer is d.(Moore and Dalley, pp 755, 761–762, 776.)The
upper and lower subscapular nerves. The upper and lower subscapular
nerves innervate the subscapularis muscle, which is the only muscle of the
rotator cuff group that medially rotates the arm. The lower subscapular
nerve also innervates the teres major muscle, which is notpart of the rota-
tor cuff group. The suprascapular nerve (answer b) innervates the
supraspinatus and infraspinatus muscles that abduct and laterally rotate
the arm, respectively. The teres minor muscle, innervated by the axillary
nerve (answer a),also laterally rotates the arm. The thoracodorsal nerve
(answer c),originating from the posterior cord between the upper and
lower subscapular nerves, innervates the latissimus dorsi muscle.
453.The answer is b.(Moore and Dalley, pp 502–504, 746.)Herniations
of intervertebral disks occur most frequently at L4–L5, L5–S1, and C6–C7.
The diminished triceps function in the right arm, as indicated by the inabil-
ity to shoot three-point shots and do pushups, points to a weakened tri-
ceps. The triceps tendon reflex is principally mediated by C7. Spinal nerve
C7 comes out between sixth and seventh cervical vertebrae [thus not
(answer c)] and is most likely compromised by herniation at C6–C7 disk.
The dermatomal pattern of pain down the posterior surface of the arm and
hand and onto the middle finger is also consistent with C7. MRI [thus not
(answers a, d, and e)] is the most useful radiological imaging study for
viewing soft tissue structures such as herniated disks. CT is much less
useful at visualizing soft structures.
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