Editing Trigeminal nerve (section)

==={{anchor|Touch/position sensation}}Touch-position sensation===
[[File:Sensory Homunculus.png|thumb|right|250px|alt=Diagram of functions controlled by the cerebral cortex|Cortical homunculus]]
Touch-position information from the body is sent to the [[ventral posterolateral nucleus]] (VPL) of the thalamus. Touch-position information from the face is sent to the [[ventral posteromedial nucleus]] (VPM) of the thalamus. From the VPL and VPM, information is projected to the [[Postcentral gyrus|primary somatosensory cortex]] (SI) in the [[parietal lobe]].

The representation of sensory information in the postcentral gyrus is organized [[Somatotopic arrangement|somatotopically]]. Adjacent areas of the body are represented by adjacent areas in the cortex. When body parts are drawn in proportion to the density of their innervation, the result is a "little man": the [[cortical homunculus]].

Many textbooks have reproduced the outdated [[Wilder Penfield|Penfield]]-Rasmussen diagram [ref?], with the toes and genitals on the [[Dental terminology#Mesial|mesial]] surface of the cortex when they are actually represented on the convexity.<ref name="pmid15976087">{{cite journal | vauthors = Kell CA, von Kriegstein K, Rösler A, Kleinschmidt A, Laufs H | title = The sensory cortical representation of the human penis: revisiting somatotopy in the male homunculus | journal = The Journal of Neuroscience | volume = 25 | issue = 25 | pages = 5984–5987 | date = June 2005 | pmid = 15976087 | pmc = 6724806 | doi = 10.1523/JNEUROSCI.0712-05.2005 | doi-access = free }}</ref> The classic diagram implies a single primary sensory map of the body, when there are multiple primary maps. At least four separate, anatomically distinct sensory homunculi have been identified in the postcentral gyrus. They represent combinations of input from surface and deep receptors and rapidly  and slowly adapting peripheral receptors; smooth objects will activate certain cells, and rough objects will activate other cells.

Information from all four maps in SI is sent to the secondary sensory cortex (SII) in the parietal lobe. SII contains two more sensory homunculi. Information from one side of the body is generally represented on the opposite side in SI, but on both sides in SII. Functional MRI imaging of a defined stimulus (for example, stroking the skin with a toothbrush) "lights up" a single focus in SI and two foci in SII.