The acoustic reflex involves contraction of which muscle and is mediated by which cranial nerve?

The acoustic reflex involves contraction of which muscle and is mediated by which cranial nerve?

• A. Tensor tympani muscle and vestibulocochlear nerve
• B. Stapedius muscle and facial nerve
• C. Stapedius muscle and trigeminal nerve
• D. Tensor tympani muscle and glossopharyngeal nerve

Answer: (B)

The acoustic reflex is the sudden contraction of the stapedius muscle in the middle ear in response to a loud sound. This action stiffens the ossicular chain and helps dampen energy reaching the inner ear. The motor signal that drives this contraction travels along the facial nerve (the seventh cranial nerve), which serves as the efferent limb of the reflex. The tensor tympani, a different middle-ear muscle, is innervated by a branch of the trigeminal nerve and is not part of this reflex. So the best pairing is the stapedius muscle with the facial nerve.

The acoustic reflex is the sudden contraction of the stapedius muscle in the middle ear in response to a loud sound. This action stiffens the ossicular chain and helps dampen energy reaching the inner ear. The motor signal that drives this contraction travels along the facial nerve (the seventh cranial nerve), which serves as the efferent limb of the reflex. The tensor tympani, a different middle-ear muscle, is innervated by a branch of the trigeminal nerve and is not part of this reflex. So the best pairing is the stapedius muscle with the facial nerve.