QUESTION: 73

You are examining a 12-year-old male patient who has a slowly enlarging, painless swelling in the left inferior region of the neck. After careful palpation and consideration of the results of the radioimaging studies, you diagnose a branchial cyst in the left inferior parathyroid gland. This gland arose in development from which of the following pharyngeal pouches?

fifth
first
fourth
second
third

Answer(s): E

Explanation:

The inferior parathyroid glands and the thymus arise from the third pharyngeal pouch. The superior parathyroid glands develop from the fourth pharyngeal pouch (choice C). The fifth pharyngeal pouch (choice A) in the human is rudimentary or absent. The first pharyngeal pouch (choice B) gives rise to the tympanic membrane, tympanic cavity, mastoid antrum, and pharyngotympanic tube. The palatine tonsil along with the tonsillar sinus and crypts develop from the second pharyngeal pouch (choice D).

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QUESTION: 74

Regarding the axon of the second-order neuron in the pathway for conscious awareness of fine, discriminative touch and vibratory sensation from the upper limb, which of the following is correct?

ascends the brainstem in the medial lemniscus
decussates in the ventral white commissure of the spinal cord
has its cell body in the nucleus gracilis
is found in the dorsal funiculus of the spinal cord
terminates in the nucleus cuneatus

Answer(s): A

Explanation:

The sensations of discriminative touch and vibration are transmitted through the medial lemniscus. Pain and temperature pathways decussate in the ventral white commisssure (choice B). The nucleus gracilis (choice C) contains neurons that process sensory signals from the lower extremity. The second-order fibers carrying discriminative touch and vibration from the upper limb originate from neurons in the nucleus cuneatus (choice E). First order fibers are found in the dorsal funiculus (choice D).

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QUESTION: 75

A 60-year-old male patient is brought to the hospital following sudden onset of weakness and sensory loss in the right face and upper limb. The right lower limb is unaffected. An MRI scan would reveal signs of a stroke in which of the following areas?

in the territory of the left anterior cerebral artery
in the territory of the left middle cerebral artery
in the territory of the left posterior cerebral artery
in the territory of the right middle cerebral artery
in the territory of the right posterior cerebral artery

Answer(s): B

Explanation:

Because the right side of the patient is affected, the stroke is in the territory of the left middle cerebral artery. This artery supplies the lateral aspect of the cerebral hemisphere, including portions of the pre- and postcentral gyri corresponding to the head, upper limb, and trunk on the primary motor (area 4 of Brodmann) and primary sensory (area 3, 1, 2 of Brodmann) cortical strips. These cortical control areas for the right lower limb are supplied by branches of the left anterior cerebral rtery (choice A), which is uninvolved in this case since the lower limb is intact. The left posterior cerebral artery (choice C) supplies the occipital and temporal lobes and is unaffected in this case. Since the right side of the brain controls the left side of the body and the patient is intact on the left side, none of the right side cerebral arteries (choices D and E) are involved.

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QUESTION: 76

An 18-year-old male patient was thrown from a horse and suffered extensive damage to the back and pelvic region. After 2 weeks of recovery, it is noted that the patient has a spastic neurogenic urinary bladder. Although the patient is unable to initiate micturition, the bladder periodically empties itself. Where is the lesion affecting control of the bladder in this patient located?

cauda equine
spinal cord, above the level of S2
spinal cord, at the level of S2
spinal cord, at the level of S3
spinal cord, at the level of S4

Answer(s): B

Explanation:

Since the patient presents with a spastic neurogenic bladder, the lesion is in the spinal cord above the level of S2. The micturition reflex works as follows: when the bladder becomes distended, sensory impulses travel back from the bladder to synapse onto preganglionic parasympathetic neurons located at the levels of S2-S4. These neurons, in turn, excite postganglionic parasympathetic neurons which innervate and cause contraction of the detrusor muscle of the urinary bladder, thus emptying the bladder. This primitive reflex loop comes under supraspinal influence in early childhood when the child learns control of the micturition reflex. When the supraspinal influence is removed, as happens with spinal lesions above the level of S2, the primitive reflex loop remains and the neurogenic spastic bladder empties itself reflexively whenever it becomes full. Lesions in the cauda equina (choice A), or in the spinal cord at the level of S2 (choice B), S3 (choice D), or S4 (choice E) will result in a flaccid bladder because of loss of innervation to the detrusor muscle. In this case, the bladder does not contract by itself and the patient will have to be catherized to prevent cystitis.

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QUESTION: 73

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QUESTION: 75

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