Here’s an example of a question from Askdoc USMLE Step 1 Prep Course Q Bank. We also post this Q&A in our Askdoc Facebook Fan Page. Try to practice answering the question before peeking into the answer.
Question # 1:
In fractures of the surgical neck of the humerus, the axillary nerve is commonly damaged. This causes numbness on the lateral side of the arm. Cell bodies involved in the sensory loss are located in which of the following structures?
a.) Anterior horn of the spinal cord
b.) Lateral horn of the spinal cord
c.) Posterior horn of the spinal cord
d.) Dorsal root ganglion
e.) Sympathetic chain ganglia
Check out the Answer below:
a.) Anterior horn of the spinal cord is incorrect. The cell bodies of the general somatic efferent (GSE) neurons are located in the anterior horn of the spinal cord. These neurons innervate skeletal muscle of somatic origins.
b.) Lateral horn of the spinal cord is incorrect. The lateral horn of the spinal cord contains the cell bodeies of preganglionic sympathetic neurons in spinal cord segments T1-L2. These are general visceral efferent fibers (GVE).
c.) Posterior horn of the spinal cord is incorrect. The posterior horn of the spinal cord contain cell bodies of second-order afferent pain and temperature fibers synapse on these cell bodies and their dendrites.
d.) Dorsal root ganglion is correct. General somatic afferent (GSA) neurons carry sensation from skin, muscle, bone and joints. The cell bodies of these pseudo unipolar first order afferent neurons are located in the dorsal root ganglia. Their peripheral processes are carried in spinal nerves while their central processes enter the spinal cord via the dorsal root.
e.) Sympathetic chain ganglia is incorrect. The sympathethic chain ganglia contain the cell bodies of postganglionic sympathetic neurons.
This is an example of a straightforward facts-based question. If you know the fact, you can get the right answer. If you open a textbook, you can verify the right answer. If you like a challenge, try question number 2. This is an easy question masquerading as a tough question. You can know all the facts, take as much time to research your answer by reading up on textbooks and googling them and still get your answer wrong. Although only about 25% of USMLE questions are of this kind, it accounts for the reputation of USMLE as a tough exam. There is a way to more consistently get the right answer to these type of questions.
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