Editing Trigeminal nerve (section)

===Sensory pathways===
Sensory pathways from the periphery to the cortex are separate for touch-position and pain-temperature sensations. All sensory information is sent to specific nuclei in the [[thalamus]]. Thalamic nuclei, in turn, send information to specific areas in the [[cerebral cortex]]. Each pathway consists of three bundles of nerve fibers connected in series:

[[File:Sensory Pathways III.png|center|alt=Flow chart from sensory receptors to the cerebral cortex]]
The secondary neurons in each pathway [[decussate]] (cross the spinal cord or brainstem), because the spinal cord develops in segments. Decussated fibers later reach and connect these segments with the higher centers. The [[optic chiasm]] is the primary cause of decussation; nasal fibers of the optic nerve cross (so each cerebral hemisphere receives contralateral—opposite—vision) to keep the [[interneuron]]al connections responsible for processing information short. All sensory and motor pathways converge and diverge to the contralateral hemisphere.<ref>Excerpt from [https://archive.org/details/cunninghamstextb00cunn ''Cunningham's Textbook of Anatomy'']</ref>

Although sensory pathways are often depicted as chains of individual neurons connected in series, this is an oversimplification. Sensory information is processed and modified at each level in the chain by interneurons and input from other areas of the nervous system. For example, cells in the main trigeminal nucleus (Main V in the diagram below) receive input from the [[reticular formation]] and cerebellar cortex. This information contributes to the final output of the cells in Main V to the thalamus.

[[File:Touch Pain Pathways.png|thumb|600px|center|alt=Text-and-line diagram of sensory-nerve pathways|C = Cervical segment, S = Sacral segment, VPL = [[Ventral posterolateral nucleus]], SI = [[Primary somatosensory cortex]], VM = [[Ventromedial prefrontal cortex]], MD = [[Medial dorsal thalamic nucleus]], IL = [[Intralaminar nucleus]], VPM = [[Ventral posteromedial nucleus]], Main V = [[Main trigeminal nucleus]], Spinal V = [[Spinal trigeminal nucleus]]]]

Touch-position information from the body is carried to the thalamus by the [[medial lemniscus]], and from the face by the [[trigeminal lemniscus]] (both the anterior and posterior trigeminothalamic tracts). Pain-temperature information from the body is carried to the thalamus by the [[spinothalamic tract]], and from the face by the anterior division of the [[trigeminal lemniscus]] (also called the [[anterior trigeminothalamic tract]]).

Pathways for touch-position and pain-temperature sensations from the face and body merge in the brainstem, and touch-position and pain-temperature sensory maps of the entire body are projected onto the thalamus. From the thalamus, touch-position and pain-temperature information is projected onto the cerebral cortex.