The trigeminal nerve has two roots, motor and sensory.
(a) Motor; the motor nucleus is situated in the tegmental portion of the pons, on the medial side of the main sensory nucleus; (b) sensory; these fibres arise from the nerve cells of the Gasserian (semilunar) ganglion. They terminate in the main sensory nucleus in the tegmentum of the pons, and also in a column of grey matter continuous with the substantia gelatinosa of the spinal cord.
A mesencephalic root issues from the grey matter around the aqueduct of Sylvius; authorities differ as to whether this root joins the motor or sensory part of the trigeminal.
The roots emerge from the lateral aspect of the pons, and proceeding forwards enter a small pocket of dura mater, the cavum Meckelii.
In the cavum Meckelii a large ganglion, the Gasserian (semilunar), develops upon the sensory root. The ganglion lies in the middle cranial fossa near the apex of the petrous portion of the temporal bone. The motor root of the trigeminal passes beneath the ganglion. It is important to note the chief relations of the ganglion, namely the cavernous sinus on the medial side, and the internal carotid artery, which is first inferior then medial. Three trunks arise from the anterior border of the ganglion; the ophthalmic and superior maxillary divisions are entirely sensory; the inferior maxillary division is a mixed nerve, as it is joined by the motor root.