Editing Somatic nervous system (section)

== Structure ==
There are 43 segments of nerves in the human body.<ref name="Rea_2014">{{Cite book|chapter-url=https://www.sciencedirect.com/science/article/pii/B9780128008980000191|chapter=Introduction to the Nervous System|date=2014-01-01|publisher=Academic Press|isbn=978-0-12-800898-0|language=en|doi=10.1016/b978-0-12-800898-0.00019-1|title=Clinical Anatomy of the Cranial Nerves| vauthors = Rea P |pages=xv-xxix}}</ref> With each segment, there is a pair of sensory and motor nerves. 31 segments of nerves are in the spinal cord and 12 are in the brain stem.<ref name="Rea_2014" /> [[Interneuron]]s also known as '''association neurons''' are present throughout the central nervous system forming links between the sensory and motor fibres.<ref name="SEER2024">{{cite web |title=Nerve Tissue {{!}} SEER Training |url=https://training.seer.cancer.gov/anatomy/nervous/tissue.html |website=training.seer.cancer.gov |access-date=19 August 2024}}</ref>
Thus the somatic nervous system consists of two parts:
* [[Spinal nerve]]s: They are [[mixed nerve]]s that carry sensory information into and motor commands out of the spinal cord.<ref name="Felten_2016">{{Citation| vauthors = Felten DL, O'Banion MK, Maida MS | chapter = 9 - Peripheral Nervous System|date= January 2016 | veditors = Felten DL, O'Banion MK, Maida MS | title = Netter's Atlas of Neuroscience | edition = Third |pages=153–231 |place=Philadelphia |publisher=Elsevier |language=en |doi=10.1016/b978-0-323-26511-9.00009-6 |isbn=978-0-323-26511-9}}</ref> The spinal nerves serve as a bridge between the environment and the central nervous system (CNS). These neurons work together to transfer autonomic, sensory, and motor impulses from the spinal cord to the body's other systems. The spinal nerves are arranged into 31 pairs according to the regions of the spinal cord. To be more precise, there are eight pairs of [[cervical nerves]] (C1–C8), twelve pairs of [[thoracic nerves]] (T1–T12), five pairs of [[lumbar nerves]] (L1–L5), five pairs of [[sacral nerves]] (S1–S5), and one pair of [[coccygeal nerves]]. Peripheral nerves are included in the category of peripheral nervous system.<ref>{{cite book | vauthors = Kaiser JT, Lugo-Pic JG | chapter = Neuroanatomy, Spinal Nerves |date=2024 | title = StatPearls | chapter-url = http://www.ncbi.nlm.nih.gov/books/NBK542218/ |access-date=2024-01-26 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=31194375 }}</ref>
* [[Cranial nerves]]: They are the nerve fibers that carry information into and out of the brain stem.<ref name="Rea_2014" /> They include smell, eye muscles, mouth, taste, ear, neck, shoulders, and tongue.<ref name="Felten_2016" /> Partially innervating the head and neck structures are the cranial nerves, which supply afferent and efferent functions. Neural processes connected to certain brainstem nuclei and cortical regions make up cranial nerves, in contrast to [[spinal nerves]], which have neural fibers originating from the spinal grey matter as their roots.<ref>{{cite book | vauthors = Sonne J, Lopez-Ojeda W | chapter = Neuroanatomy, Cranial Nerve |date=2024 | title = StatPearls | chapter-url = http://www.ncbi.nlm.nih.gov/books/NBK470353/ |access-date=2024-01-26 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29261885 }}</ref> The cranial nerves VIII (vestibulocochlear), II (optic), and I (olfactory) are regarded as entirely afferent. The exclusively efferent cranial nerves are XI (spinal accessory), XII (hypoglossal), VI (abducens), IV (trochlear), and III (oculomotor). The remaining cranial nerves, X (vagus), IX (glossopharyngeal), VII (facial), and V (trigeminal), have mixed sensory and motor functions.<ref>{{cite journal | vauthors = Traylor KS, Branstetter BF | title = Cranial Nerve Anatomy | journal = Neuroimaging Clinics of North America | volume = 32 | issue = 3 | pages = 565–576 | date = August 2022 | pmid = 35843663 | doi = 10.1016/j.nic.2022.04.004 | series = Neuroimaging Anatomy, Part 1: Brain and Skull | s2cid = 250568029 }}
</ref> Anatomically, cranial nerves are numbered from I to XII, which indicates their sequential origin from the caudal to the ventral brainstem. Alternatively, they can be postulated in groups based on the developmental functions they perform (sensory, motor, mixed).