trigeminal

Trigeminal nerve, or cranial nerve V, is a mixed peripheral nerve that provides sensory innervation to the face and motor control for the muscles of mastication. It originates from the brainstem and splits into three major divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3).

V1 and V2 are purely sensory, conveying sensation from the forehead, scalp, eyelids, cornea, nose, cheeks, upper lip, and palate. V3 is mixed, carrying sensory input from the lower face, mucosa of the mouth, and anterior two-thirds of the tongue, and motor fibers to the muscles of mastication. The motor component of V3 also innervates associated structures via branchial motor fibers.

The trigeminal nerve arises with a large sensory root and a smaller motor root and contains a sensory ganglion, the trigeminal (Gasserian) ganglion, located in Meckel's cave. After the ganglion, the three divisions travel to their targets: V1 through the superior orbital fissure; V2 through the foramen rotundum; V3 through the foramen ovale. The motor fibers join V3 to reach the muscles of mastication and related muscles such as the tensor tympani and tensor veli palatini.

Central connections include the trigeminal sensory nuclei in the brainstem: the principal (chief) sensory nucleus, the spinal trigeminal nucleus, and the mesencephalic nucleus, which process discriminative touch, pain, temperature, and proprioception. Afferent information contributes to reflexes such as the corneal reflex, with V1 providing the sensory limb.

Clinical relevance includes trigeminal neuralgia, characterized by sudden, severe unilateral facial pain in V2/V3 distributions. Lesions or compression can cause sensory loss or impaired mastication.