Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), in contrast to spinal nerves (which emerge from segments of the spinal cord). Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck. Spinal nerves emerge sequentially from the spinal cord with the spinal nerve closest to the head emerging in the space above the first cervical vertebra. The cranial nerves, however, emerge from the central nervous system above this level. Each cranial nerve is paired and is present on both sides. Depending on definition in humans there are twelve or thirteen cranial nerves pairs, sometimes also including cranial nerve zero. The numbering of the cranial nerves is based on the order in which they emerge from the brain, front to back (brainstem). The terminal nerves, olfactory nerves (I) and optic nerves (II) emerge from the cerebrum or forebrain, and the remaining ten pairs arise from the brainstem, which is the lower part of the brain.
Function of the cranial nerves:
- The cranial nerves serve functions such as smell, sight, eye movement, and feeling in the face. The cranial nerves also control balance, hearing, and swallowing.
- The twelve cranial nerves, in order from I to XII are: olfactory nerve, optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharengeal nerve, vagus nerve, spinal accessory nerve, and hypoglossal nerve.
- The vagus nerve (X) has many branches and is responsible for tasks including heart rate, gastrointestinal peristalsis, sweating, and muscle movements in the mouth, including speech and keeping the larynx open for breathing.
- The olfactory nerve (I): This is instrumental for the sense of smell,
it is one of the few nerves that are capable of regeneration.
- The optic nerve (II): This nerve carries visual information from
the of the eye to the brain.
- The oculomotor nerve (III): This controls most of the eye's movements,
the constriction of the , and maintains an open eyelid.
- The trochlear nerve (IV): A motor nerve that the superior oblique muscle of
the eye, which controls rotational movement.
- The trigeminal nerve (V): This is responsible for and motor function in the face
- The abducens nerve (VI): A motor nerve that innervates the of the eye, which controls
- The facial nerve (VII): This controls the muscles of facial
expression, and functions in the conveyance of taste sensations from the
anterior two-thirds of the tongue and oral cavity.
- The vestibulocochlear nerve
(VIII): This is responsible for
transmitting sound and (balance) information from the to the brain.
- The glossopharyngeal nerve
(IX): This nerve receives sensory information
from the , the , the middle ear, and the rest of
- The vagus nerve (X): This is responsible for many tasks, including
heart rate, gastrointestinal peristalsis, sweating, and muscle movements in the
mouth, including speech and keeping the larynx open for breathing.
- The spinal accessory (XI): This nerve controls specific muscles of the
shoulder and neck.
- The hypoglossal nerve (XII):
This nerve controls the tongue movements of speech, food
manipulation, and swallowing.