The recurrent laryngeal nerve (RLN) is a branch of the vagus nerve (Cranial Nerve X). Originating in the brainstem, the vagus nerve travels down into the torso, where the RLN detaches and begins its unusual course. This nerve controls nearly all movement of the vocal cords, regulating the opening and closing of the voice box. This mechanism is necessary for both vocalization and airway protection.
The Unique Recurrent Pathway
The nerve receives its name, “recurrent,” because its anatomical path involves descending into the chest cavity before looping back upward toward the larynx in the neck. This unusual detour is a remnant of embryonic development, resulting in a long course. The right and left recurrent laryngeal nerves follow asymmetrical paths, dictated by their interaction with major blood vessels in the upper chest.
The right RLN branches from the vagus nerve higher in the neck and loops underneath the right subclavian artery. Conversely, the left RLN has a much longer and deeper trajectory, descending further into the chest before wrapping underneath the arch of the aorta near the heart. After their respective loops, both nerves ascend along the trachea and esophagus, eventually entering the larynx from below to reach their target muscles. This long, circuitous pathway explains why the nerve is vulnerable to injury from conditions or procedures in the neck or chest.
Muscles Controlled for Voice Production
The recurrent laryngeal nerve provides motor control to the intrinsic muscles of the larynx. It innervates every intrinsic laryngeal muscle with a single exception: the cricothyroid muscle. The cricothyroid muscle, which controls pitch and vocal cord tension, is instead supplied by the superior laryngeal nerve, another branch of the vagus nerve.
The RLN controls the muscles that govern the opening and closing of the vocal cords, actions known as abduction and adduction, respectively. The posterior cricoarytenoid muscles are the sole muscles responsible for vocal cord abduction, actively pulling the cords apart to open the airway for breathing. They are the only laryngeal muscles that widen the space between the vocal folds.
All other RLN-innervated intrinsic muscles, including the lateral cricoarytenoids, the thyroarytenoids, and the interarytenoids, function to adduct the vocal cords. Adduction draws the vocal cords together, allowing them to vibrate against each other to produce sound during speech. This action also provides a protective seal over the trachea during swallowing. The thyroarytenoid muscles, which are housed within the vocal cords themselves, adjust the tension to change the quality and volume of the voice.
Sensory Input and Non-Laryngeal Targets
The recurrent laryngeal nerve carries sensory fibers in addition to its motor control. It provides sensation to the mucous membrane lining the larynx in the subglottic region, the area below the vocal folds. This sensory input is important for reflexes that protect the airway.
The nerve’s influence extends beyond the larynx, as it also supplies motor and sensory fibers to other nearby structures. Before entering the larynx, the RLN gives off branches that innervate parts of the upper trachea and the esophagus. Furthermore, it supplies the inferior pharyngeal constrictor muscle, which is involved in the mechanics of swallowing. These non-laryngeal targets demonstrate the RLN’s broader role in the complex functions of the throat and upper airway.
Consequences of Nerve Injury
Damage to the recurrent laryngeal nerve, often caused by neck or chest surgery, particularly thyroid surgery, can result in functional impairment. The symptoms experienced depend on whether the damage is unilateral, affecting one nerve, or bilateral, affecting both. Unilateral injury is the more common outcome, leading to paralysis of one vocal cord, which becomes fixed in a partially open position.
The paralysis of a single vocal cord results in hoarseness and a weakened, breathy voice because the two vocal cords cannot meet fully to create a strong sound vibration. Patients may also experience difficulties with swallowing. However, the airway generally remains open enough for normal breathing.
Bilateral damage is a far more serious condition because both vocal cords become paralyzed and often settle in a closed or near-closed position. This failure to abduct the vocal cords severely restricts the size of the airway opening, leading to symptoms like stridor, a high-pitched, noisy breathing sound. Bilateral recurrent laryngeal nerve injury can quickly cause life-threatening difficulty breathing, potentially requiring an emergency procedure to secure the airway. Common causes of injury include tumors in the neck or chest, surgical trauma, and prolonged intubation.