Point 3 Intro Pathway Note Deficit Summary Clinical Overview Problems Contents Anatomy

The cell bodies of the pain and temperature fibers associated with the trigeminal nerve lie in the trigeminal ganglion (lies on the cerebral surface of the petrous bone in the middle cranial fossa). Just like cells within the dorsal root ganglia of the spinal cord, cells in the trigeminal ganglion possess peripheral and central processes. The peripheral processes of trigeminal ganglion neurons distribute to pain and temperature receptors on the face, forehead, mucous membranes of the nose, anterior two-thirds of the tongue, hard and soft palates, nasal cavities, oral cavity, teeth, and portions of cranial dura. The central processes enter the brain at the level of the pons (this is where all trigeminal sensory fibers enter the brain stem and where trigeminal motor fibers leave the brain stem). These central processes of trigeminal ganglion neurons conveying pain and temperature descend in the brain stem and comprise the SPINAL TRACT V. Fibers of spinal tract V terminate upon an adjacent cell group called the SPINAL NUCLEUS V, which forms a long cell column medial to spinal tract V (spinal tract and nucleus V form a slight elevation on the lateral surface of the caudal medulla called the tuberculum [swelling] cinereum [ashen or gray]). We are particularly concerned with the caudal most portion of spinal nucleus V, because ALL of the PAIN and TEMPERATURE fibers from the face terminate in this caudal region of the nucleus (other portions of spinal nucleus V will not be discussed). Cells within spinal nucleus V possess axons that curve medially to CROSS the midline and course rostrally close to (but not part of) the medial lemniscus. These crossed fibers retain their close association with the medial lemniscus as they ascend in the brain stem and are called the trigeminothalamic tract (TTT). Neither the crossing or ascending TTT fibers can be identified in our fiber-stained levels, since they are finely myelinated. Fibers in the TTT reach the GREAT GATEWAY TO THE CORTEX, the thalamus, where they terminate in the ventral posteromedial (VPM) nucleus. Neurons in the VPM then project to somatosensory cortex (areas 3, 1, 2; postcentral gyrus).