National Board of Chiropractic Examiners (NBCE) Practice Test

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Prepare for the National Board of Chiropractic Examiners Test. Utilize interactive quizzes and comprehensive study guides for each subject. Gain confidence and ensure you're exam-ready!

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Weakness of the biceps muscle with normal strength of the wrist extensors indicates a lesion of which nerve root?

The correct answer is: C5

The correct answer is C6. Weakness of the biceps muscle typically indicates an issue with the nerve root that is primarily responsible for its innervation. The biceps brachii muscle is mainly innervated by the musculocutaneous nerve, which derives its fibers primarily from the C5 and C6 nerve roots. However, when assessing weakness in conjunction with normal strength of the wrist extensors, it points specifically towards an impairment of the C6 nerve root. The wrist extensors are innervated by the radial nerve, which primarily receives fibers from C6 and C7. Therefore, if the wrist extensors are functioning normally while there is biceps weakness, it highlights that C6—that serves both muscle groups—is affected, but the function of the muscles innervated solely by C7 remains intact. This distinction indicates that while C5 may play a role in biceps function, the specific scenario of weakened biceps with intact wrist extensors aligns with a C6 nerve root lesion.