L:\usmle review 7 - Sinoe medical homepage.

(C)
(D)
(E)
Proprioception from the ipsilateral leg
Sweating of the ipsilateral face
Vibratory sense from the ipsilateral arm
49. The correct answer is E. At this level, the lateral portion of the dorsal columns (funiculus) is
composed of the fasciculus cuneatus. Axons carrying tactile, proprioceptive, and vibratory
information from the ipsilateral arm enter the spinal cord via the dorsal root, ascend the cord in
the fasciculus cuneatus, and synapse in the nucleus cuneatus of the caudal medulla. Secondary
neurons from this nucleus give rise to internal arcuate fibers, which decussate and ascend to the
thalamus (ventral posterolateral nucleus, VPL) as the medial lemniscus. Tertiary neurons from
the VPL project to the ipsilateral somatosensory cortex. Therefore, damage to the fasciculus
cuneatus would result in a deficit in tactile, proprioceptive, and vibratory sense in the ipsilateral
arm, because the fibers that carry this information do not cross until they reach the medulla.
Fine motor control of the fingers (choice A) would be carried principally by the ipsilateral lateral
corticospinal tract in the lateral funiculus of the cord.
Motor control of the contralateral foot (choice B) is carried by the ipsilateral corticospinal tract in
the lateral funiculus of the cord.
Proprioception from the ipsilateral leg (choice C) is carried by the fasciculus gracilis in the medial
part of the dorsal columns.
Hemianhidrosis (lack of sweating) of the face (choice D) could be produced by interruption of
sympathetic innervation to the face. The hypothalamospinal tract projects from the hypothalamus
to the intermediolateral cell column at levels T-1 to T-2. It descends the cord in the lateral
funiculus of the cord. Interruption of this tract results in Horner syndrome (miosis, ptosis,
hemianhidrosis).
50. A 61-year-old man presents with a chief complaint of difficulty swallowing. To evaluate his
dysphagia, the physician orders a barium swallow with fluoroscopy, as well as an esophagogram.
She finds that the anterior wall of the esophagus in the mid-thorax is being compressed. Which of
the following structures is most likely responsible for this compression