The Recurrent Laryngeal Nerve (RLN) is a pair of nerves responsible for controlling the majority of the muscles that allow for speech and breathing. It is well-known in anatomy for its highly unusual and looping path, which sees it travel far down into the chest before turning and ascending back up to the voice box, or larynx. This distinctive course is the reason for its name, “recurrent,” which is derived from the Latin for “running back.” The nerve’s function is centered on the delicate movements of the vocal cords, making its integrity fundamental to a person’s ability to speak, swallow, and protect their airway.
Originating from the Vagus Nerve
The Recurrent Laryngeal Nerve branches off a much larger nerve called the Vagus Nerve, or Cranial Nerve X, rather than originating directly from the brainstem. The Vagus Nerve is a major regulator of internal organs, carrying sensory and motor signals to the heart, lungs, and digestive tract, following a long path down from the head into the chest. The RLN separates from this main trunk at different, low points in the neck and upper chest on each side of the body.
The Vagus Nerve descends vertically within the neck, traveling alongside major arteries and veins in a structure known as the carotid sheath. The RLN must follow the Vagus nerve down before beginning its upward journey. The RLN is essentially a specialized motor and sensory branch of the Vagus, dedicated almost entirely to the lower part of the larynx.
The Distinctive Recurrent Path
The most defining feature of this nerve is its asymmetrical anatomical path. After branching off the Vagus, the nerve travels downward into the chest cavity before making a sharp U-turn to head back up toward the neck. This looping trajectory is what makes the nerve pair unique in the human body.
The course of the left and right RLNs is not the same because they loop under different major arteries. The Left RLN has the longer path, branching off the Vagus at the level of the aortic arch, the large curve of the main artery leaving the heart. It passes beneath this arch and the ligamentum arteriosum before beginning its ascent along the windpipe.
In contrast, the Right RLN branches off higher up in the neck, looping underneath the Right Subclavian Artery, which supplies blood to the right arm. After looping under their respective arteries, both nerves begin to travel superiorly, ascending in a groove between the trachea (windpipe) and the esophagus (food pipe). This peculiar arrangement is thought to be an evolutionary remnant from the development of the neck and chest structures.
Primary Role in Vocalization
Once the nerve ascends into the neck, its purpose is to provide motor control to the muscles of the larynx, or voice box. The RLN is the motor supply for nearly all of the intrinsic laryngeal muscles, which are located entirely within the larynx. These muscles are responsible for moving the two vocal cords, which are folds of tissue that vibrate to produce sound.
The nerve controls the opening and closing of the vocal cords, a process necessary for both speech and breathing. For instance, the posterior cricoarytenoid muscles, the only pair responsible for pulling the vocal cords apart to open the airway, are innervated by the RLN. A notable exception is the cricothyroid muscle, which is supplied by a separate branch of the Vagus Nerve and acts to lengthen and tighten the vocal cords to control pitch.
The RLN also carries sensory information from the mucous membranes within the larynx below the vocal cords. Its actions are necessary for two intertwined functions: generating voice and protecting the airway. The ability to close the vocal cords tightly is essential to prevent food or liquid from entering the lungs during swallowing.
Why Its Pathway Makes It Vulnerable
The long, looping path of the Recurrent Laryngeal Nerve is the reason it is susceptible to injury and compression from various conditions. Because the nerve travels through the neck, upper chest, and near major organs, any pathology in these areas can affect its function. The Left RLN is particularly vulnerable due to its lower origin and longer course around the aortic arch, placing it near the heart and other structures in the chest.
The nerve’s location makes it a common site of accidental damage during certain surgical procedures. Thyroid surgery, which is performed on the neck, and cardiac or esophageal surgeries in the chest, all place the RLN at risk because of its proximity to the surgical fields. The risk of temporary vocal cord paralysis after thyroid surgery, for example, ranges from about 3% to 8%, with a lower risk of permanent damage.
Damage to the nerve, whether from surgical trauma, tumors pressing on its path, or other medical conditions, results in vocal cord paralysis on the affected side. A unilateral injury typically causes hoarseness or a weak voice. If both nerves are damaged, the vocal cords may remain closed, leading to severe difficulty breathing that can be life-threatening.