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A college student receives an injury as a result of being tackled in a football game. After the game, the student is taken to a local hospital and is found to be unable to abduct and rotate the left arm at the shoulder, flex the elbow, or extend the wrist. Further examination reveals depression of the biceps reflex in this limb, though the reflex activity in the other limbs was normal. Which of the following is the most likely site of the injury?

a. Precentral gyrus

b. Basilar pons

c. Ventral horn cells at C1

d. Nerve roots of C5 to C6

e. Triceps muscle

The answer is D. (Siegel and Sapru, pp 143-146. Aminoff, pp 177, 200-218.) In this case, disruption of the root fibers of C5 to C6 (Erb palsy) involve components of the brachial plexus and affect muscle groups such as the deltoid, supraspinatus, infraspinatus, biceps, and flexor carpi radialis. These muscles govern abduction of the arm, rotation of the arm at the shoulder, and flexion of the elbow and wrist. Reflex activity would also be affected due to disturbance of both alpha and gamma motor neurons serving the biceps muscle. Lesions involving the cerebral cortex or pons, especially the region of the pyramidal tracts, would produce a UMN paralysis, which would include hyperreflexia and hypertonia. An LMN paralysis involving the ventral horn cells at C1 would not affect the brachial plexus and the muscle groups indicated in this question. The triceps muscle is not involved in producing the movements affected by the injury.

A 65-year-old woman has weakness when attempting to flex her left knee and extend the hip. Neurophysiological analysis of the affected regions reveals a reduced number of firing motor units, along with fasciculations and slowed conduction velocity. There is no depression of tendon reflexes or muscle wasting. Plantar and abdominal reflexes are normal, there is little sensory loss, and there are no signs of sphincter disturbances. Which of the following is the best explanation for this disturbance?

a. Peripheral neuropathy of nerves that exit the spinal cord at L4 to S1 on the left side of the body

b. Damage to the neuromuscular junctions associated with the nerves that exit the spinal cord between T8 and L3 on the left side

c. Degeneration of nerve cells in the ventral horn of the spinal cord between T8 and T12 of the left side

d. Degeneration of fibers contained in the lateral funiculus of the ...

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