Spinal nucleus of trigeminal nerve

Target:

• CN5 ⇒ Skin & deep tissues of the head, dura mater

• CN7 ⇒ Pinna and external acoustic meatus (thermal, pain)

• CN9 ⇒ Cutaneous area behind ear (thermal, pain)

• CN10 ⇒ Sensation from pinna, external acoustic meatus, tympanic membrane (thermal, pain)

“Spinal nucleus of trigeminal nerve extends caudally from chief sensory nucleus in the pons to the second cervical spinal segment and lies just medial to the spinal tract of trigeminal nerve. The spinal nucleus and tract of trigeminal nerve are chiefly concerned with the pain and temperature sensations. Based on the cytoarchitecture, the spinal nucleus is divided into three parts (or subnuclei): In craniocaudal direction these are: (a) pars rostralis, (b) pars interpolaris, and (c) pars caudalis (Fig. 9.4).

Main afferents of chief sensory and spinal nuclei are the central processes of cells in the trigeminal ganglion (which makes up the large sensory root). After entering the pons many of these processes divide into ascending and descending branches. Others either ascend or descend without being branched. “The ascending fibres end in the chief sensory nucleus. The descending fibres from a large bundle of fibres called spinal tract of trigeminal nerve. Fibres of the spinal tract terminate in the subjacent spinal nucleus. The afferents from three trigeminal divisions rotate, so that the fibres of ophthalmic division terminate in the pars caudalis, the fibres of maxillary division in the pars interpolaris and the fibres of mandibular division in pars rostralis.

As described earlier, the fibres ending in the chief sensory nucleus are predominantly concerned with touch, and those ending in spinal nucleus are concerned predominantly with sensations of pain and temperature.

It is important to note at this juncture that in addition to trigeminal nerve, the spinal tract receives a small component of fibres from the VIIth, IXth and Xth cranial nerves which carry the general somatic sensations from external ear, mucosa of posterior third of tongue, pharynx and larynx.

“Fibres arising from cells of chief sensory and spinal nuclei are the second order neurons (comparable to those of the spinothalamic tracts) cross to the opposite side and form a bundle called trigeminal lemniscus which ascends up and relay in the thalamus (ventral posteromedial nucleus) from where third order neurons arise and project to the sensory area of the cerebral cortex.

A separate bundle of more dorsally situated trigeminothalamic fibres (also called dorsal trigeminal lemniscus) is also described