This section describes the cranial nerves, their function, and origin/pathways when applicable.

There are 12 pairs of cranial nerves. These nerves arise from the brain and brain stem, carrying motor and or sensory information.

Cranial nerve I: Olfactory nerve

The olfactory nerve is composed of axons from the olfactory receptors in the nasal sensory epithelium. It carries olfactory information (sense of smell) to the olfactory bulb of the brain. This is a pure sensory nerve fiber.

Cranial nerve II: Optic nerve

The optic nerve is composed of axons of the ganglion cells in the eye. It carries visual information to the brain. This is a pure sensory nerve fiber. This nerve travels posteromedially from the eye, exiting the orbit at the optic canal in the lesser wing of the sphenoid bone. The optic nerves join each other in the middle cranial fossa to form the optic chiasm.

Cranial nerve III: Oculomotor nerve

The oculomotor nerve is composed of motor axons coming from the oculomotor nucleus and the edinger-westphal nucleus in the rostral midbrain located at the superior colliculus level. This is a pure motor nerve. It provides somatic motor innervation to four of the extrinsic eye muscles: the superior rectus, inferior rectus, medial rectus, and the inferior oblique muscles. It also innervates the muscles of the upper eyelid and the intrinsic eye muscles (the pupillary eye muscle.) Together, CN III, CN IV and CN VI control the six muscles of the eye.

Cranial nerve IV: Trochlear nerve

The trochlear nerve provides somatic motor innervation to the superior oblique eye muscle. This cranial nerve originates at the trochlear nucleus located in the tegmentum of the midbrain at the inferior colliculus level and exits the posterior side of the brainstem. It is also a pure motor nerve fiber.

Cranial nerve V: Trigeminal nerve

The trigeminal is the largest cranial nerve . It provides sensory information from the face, forehead, nasal cavity, tongue, gums and teeth (touch, and temperature) and provides somatic motor innervation to the muscles of mastication or “chewing”.

This cranial nerve has 3 branches: the ophthalmic, maxillary and mandibular branches.

It is composed of both sensory and motor axons. The sensory fibers are located in the trigeminal ganglion and the motor fibers project from nuclei in the pons.

Cranial nerve VI: Abducens nerve

The abducens nerve carries somatic motor innervation to one of the extrinsic eye muscles, the lateral rectus muscle. It is another pure motor nerve fiber and originates from the abducens nucleus located in the caudal pons at the facial colliculus level.

Cranial nerve VII: Facial nerve

The facial nerve carries somatic motor innervation to the many muscles for facial expression. It carries sensory information form the face (deep pressure sensation) and taste information from the anterior two thirds of the tongue. It arises at the pons in the brainstem and it emerges through openings in the temporal bone and stylomastoid foramen and has many branches. It is composed of both sensory and motor axons.

Cranial nerve VIII: Vestibulocochlear nerve

The vestibulocochlear nerve innervates the hair cell receptors of the inner ear. It carries vestibular information to the brain from the semicircular canals, utricle, and saccule providing the sense of balance. It also carries information from the cochlea providing the sense of hearing. This cranial nerve branches into the Vestibular branch (balance) and the cochlear branch (hearing). The cochlear fibers originate from the spiral ganglion. It is pure sensory nerve fiber.

Cranial nerve IX: Glossopharyngeal nerve

The glossopharyngeal nerve innervates the pharynx (upper part of the throat), the soft palate and the posterior one-third of the tongue. It carries sensory information (touch, temperature, and pressure) from the pharynx and soft palate. It carries taste sensation from the taste buds on the posterior one third of the tongue. It provides somatic motor innervation to the throat muscles involved in swallowing. It provides visceral motor innervation to the salivary glands. This cranial nerve also supplies the carotid sinus and reflex control to the heart . It is composed of both sensory and motor axons and originates from the nucleus ambiguous in the reticular formation of the medulla.

Cranial nerve X: Vagus nerve

The vagus nerve consists of many rootlets that come off of the brainstem just behind the glossopharyngeal nerve. The branchial motor component originates from the nucleus ambiguous in the reticular formation of the medulla. The visceral component originates from the dorsal motor nucleus of the vagus located in the floor of the fourth ventricle in the rostral medulla and in the central grey matt er of the caudal medulla. It is the longest cranial nerve innervating many structures in the throat, including the muscles of the vocal cords, thorax and abdominal cavity. It provides sensory information (touch, temperature and pressure) from the external auditory meatus (ear canal) and a portion of the external ear. It carries taste sensation from taste buds in the pharynx. It also provides sensory information from the esophagus, respiratory tract, and abdominal viscera (stomach, intestines, liver, etc.). It provides visceral motor innervation to the heart, stomach, intestines, and gallbladder. It is part of the ANS, the parasympathetic branch. It is composed of both sensory and motor axons. Other parasympathetic ganglia include CN III , CN VII and CN IX .

Cranial nerve XI: Spinal Accessory nerve

The spinal accessory nerve has two branches. The cranial branch provides somatic motor innervation to some of the muscles in the throat involved in swallowing. This cranial branch is accessory to CN X, originating in the caudal nucleus ambiguous, with the fibers of the cranial root traveling the same extracranial path as the branchial motor component of the vagus nerve. The spinal branch provides somatic motor innervation to the trapezius muscles, providing muscle movement for the upper shoulders head and neck. It is pure motor nerve fiber.

Cranial nerve XII: Hypoglossal nerve

The hypoglossal nerve provides somatic motor innervation to the muscles of the tongue. This pure motor nerve originates from the hypoglossal nucleus located in the tegmentum of the medulla.

Here are a few pneumonic devices to help you remember the cranial nerves and which ones carry sensory, motor or both!

*S: sensory *M: motor *B: both

Additional Study Questions