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Table 4. The Cranial Nerves

Number and Name Principal Functions
   I. Olfactory Chemical sensation; gaseous stimuli in land animals. Connects with the most rostral part of the forebrain. The nearby vomeronasal nerve (present in most vertebrates, but not in man) detects sniffed or licked liquid chemicals significant in reproduction and territorial marking. The terminal nerve (cranial nerve zero) connects with the preoptic area rather than with olfactory parts of the forebrain.

  II. Optic Vision. Not a nerve but, like the retina, part of the central nervous system. Its axons end mainly in the midbrain and thalamus.

III. Oculomotor Supplies the muscles of the eye (except those supplied by IV and VI) and the muscle that elevates the upper eyelid (in animals that have eyelids). Controls visceral functions inside the eye: constriction of pupil and focusing of lens. Nuclei are in the rostral part of the midbrain.

  IV. Trochlear Supplies one eye muscle (the superior oblique, whose tendon passes through the trochlea, a fibrous ring that serves as a pulley. Nucleus is in the caudal part of the midbrain.

   V. Trigeminal Motor to muscles of chewing and a few others near the mouth. Sensory to most of head and parts of lateral line system in fishes. Nuclei at all levels of the brain stem.

  VI. Abducent Supplies one eye muscle (the lateral rectus, which abducts the eye. Also supplies muscle of the nictitating membrane ("third eyelid") of reptiles, birds, and some mammals. Nucleus is in the caudal part of the pons.

VII. Facial Motor to muscles of face and a few others. Taste sensation. Controls lacrimal and some salivary glands. Serves parts of lateral line system in fishes. Nuclei are in the caudal part of the pons.

VIII. Vestibulocochlear Detection of position and movement (vestibular division). Hearing (auditory or cochlear division). Vestibular and cochlear nuclei are laterally located in the medulla. (Also known as stato-acoustic, acoustic or auditory nerve.)

  IX. Glossopharyngeal Supplies one muscle of swallowing (the stylopharyngeus). Controls parotid salivary gland. General and taste sensation from pharynx and posterior part of tongue. Serves parts of lateral line system in fishes. Nuclei are in the medulla.

   X. Vagus Motor to larynx, pharynx, and upper end of esophagus. Controls internal organs, including heart and much of alimentary canal. Several sensory components. In fishes, sensory from lateral line system of body and tail. The name (Latin, "wandering") is from the widespread distribution of the nerve's branches. Nuclei are in the medulla. (Has been named, pneumogastric nerve, from branches to lungs and stomach.)

The last two cranial nerves are absent in all fishes (except the Crossopterygii, which are considered by zoologists to be ancestral to limbed vertebrates) and in amphibians. Some fossil amphibians, however, had 12 cranial nerves.

  XI. Accessory Motor to some muscles that move the head. The cell bodies of the motor neurons are in the spinal cord. (Also called the spinal accessory nerve.)

XII. Hypoglossal Motor to the muscles of the tongue. The nucleus is in the caudal half of the medulla.

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Last updated: January 2003

Table 4. The Cranial Nerves
Number and Name	Principal Functions
I. Olfactory	Chemical sensation; gaseous stimuli in land animals. Connects with the most rostral part of the forebrain. The nearby vomeronasal nerve (present in most vertebrates, but not in man) detects sniffed or licked liquid chemicals significant in reproduction and territorial marking. The terminal nerve (cranial nerve zero) connects with the preoptic area rather than with olfactory parts of the forebrain.
II. Optic	Vision. Not a nerve but, like the retina, part of the central nervous system. Its axons end mainly in the midbrain and thalamus.
III. Oculomotor	Supplies the muscles of the eye (except those supplied by IV and VI) and the muscle that elevates the upper eyelid (in animals that have eyelids). Controls visceral functions inside the eye: constriction of pupil and focusing of lens. Nuclei are in the rostral part of the midbrain.
IV. Trochlear	Supplies one eye muscle (the superior oblique, whose tendon passes through the trochlea, a fibrous ring that serves as a pulley. Nucleus is in the caudal part of the midbrain.
V. Trigeminal	Motor to muscles of chewing and a few others near the mouth. Sensory to most of head and parts of lateral line system in fishes. Nuclei at all levels of the brain stem.
VI. Abducent	Supplies one eye muscle (the lateral rectus, which abducts the eye. Also supplies muscle of the nictitating membrane ("third eyelid") of reptiles, birds, and some mammals. Nucleus is in the caudal part of the pons.
VII. Facial	Motor to muscles of face and a few others. Taste sensation. Controls lacrimal and some salivary glands. Serves parts of lateral line system in fishes. Nuclei are in the caudal part of the pons.
VIII. Vestibulocochlear	Detection of position and movement (vestibular division). Hearing (auditory or cochlear division). Vestibular and cochlear nuclei are laterally located in the medulla. (Also known as stato-acoustic, acoustic or auditory nerve.)
IX. Glossopharyngeal	Supplies one muscle of swallowing (the stylopharyngeus). Controls parotid salivary gland. General and taste sensation from pharynx and posterior part of tongue. Serves parts of lateral line system in fishes. Nuclei are in the medulla.
X. Vagus	Motor to larynx, pharynx, and upper end of esophagus. Controls internal organs, including heart and much of alimentary canal. Several sensory components. In fishes, sensory from lateral line system of body and tail. The name (Latin, "wandering") is from the widespread distribution of the nerve's branches. Nuclei are in the medulla. (Has been named, pneumogastric nerve, from branches to lungs and stomach.)
The last two cranial nerves are absent in all fishes (except the Crossopterygii, which are considered by zoologists to be ancestral to limbed vertebrates) and in amphibians. Some fossil amphibians, however, had 12 cranial nerves.
XI. Accessory	Motor to some muscles that move the head. The cell bodies of the motor neurons are in the spinal cord. (Also called the spinal accessory nerve.)
XII. Hypoglossal	Motor to the muscles of the tongue. The nucleus is in the caudal half of the medulla.