The superior laryngeal nerve is a branch of the vagus nerve

Vagus nerve

The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...

. It arises from the middle of the ganglion nodosum and in its course receives a branch from the superior cervical ganglion

Superior cervical ganglion

The superior cervical ganglion , the largest of the cervical ganglia, is placed opposite the second and third cervical vertebræ. It contains neurons that supply sympathetic innervation to the face....

 of the sympathetic.

It descends, by the side of the pharynx

Pharynx

The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

, behind the internal carotid artery

Internal carotid artery

In human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain....

, and divides into two branches:

• external laryngeal nerve
  External laryngeal nerve
  The external laryngeal nerve is the smaller, external branch of the superior laryngeal nerve. It descends on the larynx, beneath the sternothyroid muscle, to supply the cricothyroid muscle....
  
  
• internal laryngeal nerve
  Internal laryngeal nerve
  The internal laryngeal nerve is the internal branch of the superior laryngeal nerve. It descends to the thyrohyoid membrane, pierces it in company with the superior laryngeal artery, and is distributed to the mucous membrane of the larynx....
  
  

Pathology

A superior laryngeal nerve palsy changes the pitch of the voice and causes an inability to make explosive sounds. If no recovery is evident three months after the palsy initially presents, the damage is most likely to be permanent. A bilateral palsy presents as a tiring and hoarse voice.
It can be injured in surgery involving the removal of the Thyroid gland (Thyroidectomy

Thyroidectomy

A thyroidectomy is an operation that involves the surgical removal of all or part of the thyroid gland. Surgeons often perform a thyroidectomy when a patient has thyroid cancer or some other condition of the thyroid gland...

)