There are 12 pairs of cranial nerves, as shown below.
| Cranial Nerve | Nuclei | Special characters |
|---|---|---|
| Olfactory (I) | Olfactory bulb | Sense of smell |
| Optic (II) | Lateral geniculate nucleus; pretectal nucleus (light reflex) | Sensory nerve; vision, coordinated eye movements; light and accommodation reflexes. |
| Oculomotor (III) | Oculomotor nucleus (motor); Edinger Westphal nucleus (parasympathetic) | Emerges from the midbrain; innervates all extraocular muscles except the superior oblique and lateral rectus. The Edinger Westphal nucleus supplies the ciliary and constrictor pupillae muscles after passing through the ciliary ganglion. |
| Trochlear (IV) | Motor nucleus | Emerges from the midbrain and supplies the superior oblique muscle. |
| Trigeminal (V) | Motor nucleus, 3 sensory nuclei - principal sensory, mesencephalic and spinal trigeminal. | Emerges from the pons; has a small motor root and a large sensory root. Motor fibers supply the muscles of mastication, mylohyoid, anterior belly of digastric, tensor tympani, and tensor veli palatini. Sensory supply is to the face and head: the principal sensory nucleus receives touch and pressure input; the mesencephalic nucleus receives proprioceptive input from the teeth, hard palate, TM joint, and muscles of mastication; the spinal trigeminal nucleus receives pain and temperature input. It has three divisions: V1 (ophthalmic), V2 (maxillary), and V3 (mandibular). |
| Abducens (VI) | Motor nucleus | Arises from the junction of the pons and medulla; the nucleus lies in the floor of the fourth ventricle; supplies the lateral rectus muscle. |
| Facial (VII) | Motor nucleus; sensory nucleus in solitary nucleus; parasympathetic superior salivatory nucleus | Emerges from the junction of the pons and medulla, lateral to the Abducens nerve; has motor and sensory roots. Parasympathetic fibers supply the submandibular and submental salivary glands. Motor fibers supply the muscles of facial expression. Sensory functions include taste from the anterior two-thirds of the tongue and skin sensation from the auricle of the ear. |
| Vestibulocochlear (VIII) | Four vestibular nuclei; dorsal and ventral cochlear nuclei | Sensory nerve. The vestibular component is involved with balance, and the cochlear component is involved with hearing. The anterior cochlear nucleus processes low-frequency sounds, while the posterior cochlear nucleus processes high-frequency sounds. |
| Glossopharyngeal (IX) | Nucleus ambiguus (motor); nucleus solitarius (sensory); inferior salivatory nucleus (parasympathetic) | Emerges from the medulla. Motor fibers supply the stylopharyngeus muscle. Parasympathetic fibers supply the parotid gland. Provides taste sensation from the posterior one-third of the tongue and receives afferents from the carotid sinus. |
| Vagus (X) | Nucleus ambiguus (motor); dorsal motor nucleus (parasympathetic); nucleus solitarius (sensory) | Emerges from the medulla. Motor fibers supply muscles of the pharynx and larynx. Parasympathetic fibers innervate the upper GIT, liver, pancreas, heart, and bronchi. The sensory nucleus receives afferents from the carotid sinus. |
| Accessory (XI) | Motor nucleus ambiguus | Arises from the medulla and C1 to C5 cervical segments; has cranial and spinal roots; innervates the trapezius and sternocleidomastoid. |
| Hypoglossal (XII) | Motor nucleus | Innervates muscles of the tongue, including hyoglossus, genioglossus, and styloglossus. |
Most cranial nerves receive bilateral upper motor neuron (UMN) innervation, meaning each cranial nerve nucleus receives input from both the left and right cerebral hemispheres. This bilateral innervation applies to muscles of the eyes, jaw, pharynx, upper face, larynx, and neck.
There are two key exceptions:
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