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25. The correct answer is A
. The recurrent laryngeal nerve is a branch of the vagus nerve, which innervates all the intrinsic laryngeal muscles except the cricothyroid muscle. The cricothyroid is attached to the cricoid cartilage and the thyroid cartilage; contraction of this muscle tends to stretch and adduct the vocal ligament. The cricothyroid is innervated by the external laryngeal nerve.

 

The lateral cricoarytenoid muscle (choice B) is innervated by the recurrent laryngeal nerve and is attached to the cricoid cartilage and the arytenoid cartilage. Its contraction causes adduction of the vocal ligament.

The posterior cricoarytenoid muscle (choice C) is innervated by the recurrent laryngeal nerve and is attached to the cricoid cartilage and the arytenoid cartilage. Its contraction causes abduction of the vocal ligament.

The thyroarytenoid muscle (choice D) is innervated by the recurrent laryngeal nerve and is attached to the thyroid cartilage and the arytenoid cartilage. Its contraction causes slackening of the vocal ligament.

 

The vocalis muscle (choice E) is the most medial part of the thyroarytenoid muscle. It attaches either to the thyroid cartilage and the vocal ligament, or to the arytenoid cartilage and the vocal ligament. It is innervated by the recurrent laryngeal nerve. Its contraction causes tension on segments of the vocal ligament.

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