USMLE® Step 1 Question of the Day: Nerve roots
Published on Sep 20, 2023. Updated on Oct 24, 2023.
A human cadaveric model is being studied to better understand the anatomic distribution and innervation of muscles in the upper extremity, chest, and back. A nerve root is stimulated with an electrical impulse, which results primarily in the contraction of the lumbricals and interossei of the hand. Which of the following accurately reflects the nerve root(s) being tested in this experiment?
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The correct answer to today's USMLE® Step 1 Question is...
A. T1Before we get to the Main Explanation, let's look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
B. C5Incorrect: Primary motor function at C5 involves deltoid and elbow flexion.
C. C6Incorrect: Primary motor function at C6 involves bicep and wrist extension.
Incorrect: Primary motor function at C7 involves triceps and wrist flexion.
Incorrect: Primary motor function at C8 involves the finger flexors.
The brachial plexus is composed of nerve roots C5-T1, divided into the upper, middle, and lower trunks, which form the lateral, posterior, and medial cords, which become the musculocutaneous, median, and ulnar branches.
Understanding cervical nerve roots' anatomic distribution and function can help predict both sensory and motor neurologic deficits. This knowledge becomes essential clinically when assessing for evidence of an anatomic lesion following a nerve root distribution.
Understanding the anatomic distribution and function of the cervical nerve roots of the brachial plexus can help predict both neurologic sensory and motor deficits.
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