Editing Onuf's nucleus (section)

==Structure==
Onuf's nucleus is a distinct group of [[neuron]]s located in the ventral part ([[Rexed laminae|lamina IX]]) of the [[Anterior horn of spinal cord|anterior horn]] of the [[Sacrum|sacral]] region of the human [[spinal cord]] involved in the maintenance of [[Urinary|micturition]] and [[Defecation|defecatory]] continence, as well as muscular contraction during [[orgasm]]. It contains [[motor neuron]]s, and is the origin of the [[pudendal nerve]]. The sacral region of the spinal cord is the fourth segment (cervical, thoracic, and lumbar being the first three) of vertebrae in the spinal cord which consists of the vertebrae 26-30.<ref name=Mannen/>

This small group of neural cells is located between S1 and S2 or S2 and S3 and although Onuf's nucleus is located primarily in S2, it can extend to the caudal end of the first sacral segment or to the middle part of the third sacral segment. Also, Onuf's nucleus is found almost symmetrically on both sides of the ventral horn. This [[Nerve|innervation]], or nerve supply, is arranged in a [[neuropil]] and averages approximately 625 neurons in both the left and right ventral horns,<ref name=Jost>{{Citation |vauthors=Jost WH, Marsalek P | date = 2005 | title = Duloxetine in the treatment of stress urinary incontinence | journal = Therapeutics and Clinical Risk Management | volume = 1 | issue = 4| pages = 259–264 | pmid = 18360568 | pmc = 1661641 | postscript = . }}</ref> and measures about 4–6&nbsp;mm on each side.<ref>{{Citation | doi = 10.1002/1531-8249(200007)48:1<97::AID-ANA14>3.0.CO;2-Z |vauthors=Scaravilli T, Pramstaller PP, Salerno A, Egarter-Vigl E, Giometto B | date = 2000 | title = Neuronal loss in Onuf's nucleus in three patients with progressive supranuclear palsy | journal = Annals of Neurology | volume = 48 | issue = 1| pages = 97–101 | pmid = 10894221 | postscript = . |display-authors=etal}}</ref> In other animals it averages approximately 300-500 on both sides.<ref name=Jost/> 

Many [[staining]] techniques have been used to study the anatomy of Onuf's nucleus. The Nissl method was commonly used as well as myelin sheath stains and silver stains. Use of the Klüver-Barrera staining method showed that Onuf's nucleus appears clear due to the presence of many vertically arranged unmyelinated fibers. The sizes of the cells in Onuf's nucleus are small in comparison to other lateral group cells. The neurons in Onuf's nucleus are motoneurons, and like most [[Motor neuron|motoneurons]] they are characterized by their multipolarity and large [[Nissl body|Nissl bodies]].<ref name=Mannen/>