The cranial nerves consist of 12 pairs of nerves that originate in the brain. They provide sensory, motor, and autonomic control of structures in the head, neck, and trunk. When something goes wrong with the cranial nerves, it can affect the senses or the ability to speak, chew, or swallow.

This article explains everything about the cranial nerves and their anatomy, function, and disorders.

The cranial nerves arise in the brain. They get their name because they exit through openings in the skull or cranium. There are 12 pairs of cranial nerves, often designated by Roman numerals.

Cranial nerves III–XII (3–12) originate in the brainstem. This structure is the top part of the spinal cord that sits inside the skull. It is responsible for reflexes, autonomic and unconscious processes, and some voluntary movements.

Learn about brainstem structure and function.

Cranial nerves I and II come from the cerebrum. The cerebrum is the most developed part of the brain. Higher functions take place there, such as language, logic, memory, and understanding.

Learn about cerebrum structure and function.

The cranial nerves carry signals between the brain and the structures they control. There are three categories of function:

Cranial nerves may be sensory, motor, autonomic, or a combination.

The trigeminal nerve is a mixed-function nerve. It carries sensory signals to the brain and motor signals from the brain.

Its sensory role is responsible for feeling in the face. Its motor function controls chewing.

The facial nerve is a mixed-function nerve.

It controls facial expression with motor signals from the brain. It plays a role in taste by carrying signals from the front of the tongue to the brain.

The facial nerve also controls some autonomic functions, such as tear production and salivation.

The vestibulocochlear nerve is responsible for the sense of hearing and the vestibular sense. Your vestibular sense gives you information about your head position and the position of your body in space.

This nerve also contributes to balance and smooth movements. It allows you to perceive gravity.

The glossopharyngeal nerve is a mixed-function nerve.

Its motor signals control the muscles for swallowing. Its sensory signals carry information about taste from the back of the tongue, feeling in the tongue, and the back of the throat.

The 9th cranial nerve can sense feelings from the middle ear and helps with automatic control of salivary glands.

The vagus nerve is a mixed-function nerve.

It controls the muscles of the throat and voice box. It is also the main nerve of the parasympathetic nervous system. It operates many automatic processes, such as heart rate and digestion.

The accessory nerve connects to the sternocleidomastoid muscle, which runs from the breastbone (sternum) and collarbone to the skull.

The sternocleidomastoid is the prominent muscle you can see on either side of the neck. The accessory nerve also connects to the trapezius muscle in the shoulder.

Disorders and conditions of the cranial nerves can involve one or more nerves. The causes and symptoms of cranial nerve disorders often overlap. Conditions that can affect cranial nerves include:

Because the cranial nerves come in pairs — for each side of your body — tests for cranial nerve function evaluate symmetry: Is the change on both sides equally, or is one of the nerve pairs affected more than the other? Evaluations include:

Treatment for cranial nerve dysfunction depends on the cause. In general, doctors recommend nonsurgical treatments first. Sometimes surgery is necessary. 

Seunggu Han, MD, reviewed the following frequently asked questions.

Cranial nerve 2 is the optic nerve. It is responsible for your sense of sight. It connects to the eye’s retina, the light-sensing part at the back of the eyeball. The optic nerve carries signals from the retina to the brain. The brain interprets the signals as vision.

The largest is the trigeminal nerve. This is cranial nerve V (5th cranial nerve). The longest cranial nerve is the vagus nerve or cranial nerve X. “Vagus” means wandering or straying in Latin. The nerve branches and spreads to innervate several organs and systems.

Vision is possible because of the optic nerve. It is cranial nerve II, also known as the 2nd cranial nerve.

The 12 pairs of cranial nerves arise directly out of the brain. They provide nerve supply to the organs and structures in the head and neck. However, the vagus nerve plays a role in various bodily autonomic functions and supplies several organs. Learn more about the autonomic nervous system.

The cranial nerves are responsible for our senses. They are also the source of movement for the face, neck, and shoulders.   

Learn about the central nervous system here.

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