Superior laryngeal

Superior laryngeal nerve is a branch of the vagus nerve (cranial nerve X) that supplies motor function and sensation to parts of the larynx. It is a key component in the anatomy and physiology of voice production and swallowing. The superior laryngeal nerve itself divides into two major branches: the internal laryngeal nerve and the external laryngeal nerve, each serving different functions within the larynx.

Anatomy

The superior laryngeal nerve branches off from the vagus nerve just below the level of the jugular foramen. As it courses downwards, it divides into its two primary branches, the internal and external laryngeal nerves, at the level of the hyoid bone.

Internal Laryngeal Nerve

The internal laryngeal nerve enters the larynx through the thyrohyoid membrane along with the superior laryngeal artery. It provides sensory innervation to the mucosa above the vocal cords, including the epiglottis, aryepiglottic fold, and the internal surface of the larynx. This sensory function is crucial for the cough reflex and protection of the airway during swallowing.

External Laryngeal Nerve

The external laryngeal nerve, in contrast, provides motor innervation to the cricothyroid muscle, which is involved in tensioning the vocal cords and thus plays a significant role in pitch regulation during phonation. It descends along the neck, lying in close proximity to the superior thyroid artery.

Clinical Significance

Injury to the superior laryngeal nerve can result from surgical procedures in the neck, particularly thyroidectomy, or from trauma. Such injury can lead to a variety of symptoms, depending on which branch is affected. Damage to the internal laryngeal nerve can result in a loss of sensation in the larynx, leading to an increased risk of aspiration and a diminished cough reflex. Injury to the external laryngeal nerve can cause weakness or paralysis of the cricothyroid muscle, resulting in voice changes, particularly an inability to tense the vocal cords and a decrease in the pitch range.

Diagnosis and Treatment

Diagnosis of superior laryngeal nerve injury typically involves a combination of patient history, physical examination, and possibly laryngoscopy to visualize the vocal cords and assess their function. Treatment depends on the severity and cause of the injury but may include voice therapy, surgical intervention, or management of underlying conditions contributing to nerve damage.

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