The recurrent laryngeal nerve is a branch of the vagus nerve (cranial nerve X) that provides innervation to various structures in the neck, especially the larynx. It plays an essential role in speech, swallowing, and breathing.
Structure
- Fiber Types: The recurrent laryngeal nerve is a mixed nerve, containing both sensory and motor fibers. These fibers are responsible for the sensation and motor control of several laryngeal structures.
- Branching: As it ascends towards the larynx, the recurrent laryngeal nerve gives off several branches that supply the trachea, esophagus, and various laryngeal muscles.
Location
- Origin: The recurrent laryngeal nerve branches off from the vagus nerve. Its origin varies slightly depending on whether it is the left or right recurrent laryngeal nerve.
- Course – Right Side: On the right side, the nerve diverges from the vagus nerve around the level of the subclavian artery, looping under it before ascending alongside the trachea toward the larynx.
- Course – Left Side: On the left side, the nerve diverges from the vagus nerve at the level of the aortic arch, looping under the aorta before ascending.
- Pathway in Neck: Both the left and right recurrent laryngeal nerves ascend in the tracheoesophageal groove, closely related to the trachea and esophagus, en route to the larynx.
- Laryngeal Entry: The nerve enters the larynx posteriorly, usually passing behind the cricothyroid joint. It innervates all intrinsic muscles of the larynx except for the cricothyroid muscle, which is innervated by the external branch of the superior laryngeal nerve.
- Sensory Innervation: The recurrent laryngeal nerve provides sensory innervation to the laryngeal mucosa below the vocal cords.
Functions
The recurrent laryngeal nerve serves both sensory and motor functions primarily related to the larynx.
Here are some of it’s main functions:
Motor Functions
Intrinsic Laryngeal Muscles: The recurrent laryngeal nerve supplies all the intrinsic muscles of the larynx except the cricothyroid muscle. These muscles are responsible for vocal cord movement, allowing for the complex adjustments necessary for speech, singing, and breath control.
Vocal Cord Adduction and Abduction: The nerve enables the vocal cords to move towards each other (adduction) and away from each other (abduction). This allows for the modulation of pitch and tone during speech and singing, and also facilitates the closing of the airway during swallowing to prevent aspiration.
Sensory Functions
Laryngeal Sensation: The recurrent laryngeal nerve provides sensory innervation to the larynx below the vocal cords. This sensory feedback is important for the coordination of swallowing and breathing.
Mucosal Sensation: It also plays a role in providing sensation to the mucosal lining of the lower larynx, which is crucial for triggering protective reflexes like coughing when irritants are present.
Integrated Functions
- Swallowing: The sensory and motor functions of the recurrent laryngeal nerve contribute to the complex process of swallowing, helping to ensure that the airway is closed off to prevent aspiration of food or liquid into the lungs.
- Cough Reflex: The sensory input from the nerve helps initiate the cough reflex, which serves to protect the airway from irritants or aspirated material.
- Voice Modulation: By controlling the intrinsic muscles of the larynx (except the cricothyroid muscle), the recurrent laryngeal nerve plays a critical role in voice modulation, including pitch and volume.
- Breathing: During breathing, the recurrent laryngeal nerve helps keep the airway open by controlling the abduction of the vocal cords, thereby facilitating airflow into and out of the lungs.
Clinical significance
The recurrent laryngeal nerve holds significant clinical importance due to its key roles in voice production, swallowing, and breathing.
Surgical Risks
- Thyroid Surgery: The recurrent laryngeal nerve is at risk of injury during thyroid surgeries. Damage to the nerve can result in vocal cord paralysis, voice changes, and even respiratory distress if both sides are affected.
- Cardiothoracic Surgery: In surgeries involving the thorax, especially those near the aorta or subclavian artery, the recurrent laryngeal nerve is at risk, particularly on the left side.
- Laryngeal Surgery: Procedures involving the larynx for conditions such as cancer or vocal cord nodules also pose a risk to the recurrent laryngeal nerve.
Voice and Swallowing
- Voice Disorders: Injury or dysfunction of the recurrent laryngeal nerve can lead to hoarseness, breathiness, and other voice disorders, impacting a patient’s ability to speak or sing.
- Dysphagia: Impairment in the nerve function can affect the process of swallowing, increasing the risk of aspiration, which can lead to pneumonia.
Respiratory Concerns
- Airway Management: The nerve plays a role in keeping the airway open. Bilateral damage to the recurrent laryngeal nerves can lead to airway obstruction, a medical emergency.
- Chronic Cough: A non-functional recurrent laryngeal nerve can impact the cough reflex, reducing the body’s ability to clear the airway of irritants.
Diagnostic Importance
- Laryngoscopy: In cases of unexplained voice changes or chronic cough, the integrity of the recurrent laryngeal nerve may be evaluated using laryngoscopy.
- Nerve Monitoring: Intraoperative neural monitoring is sometimes used during surgeries that pose a risk to the recurrent laryngeal nerve to help avoid injury.
