Editing Central nervous system (section)

==Overview==
In [[vertebrates]], the brain and spinal cord are both enclosed in the [[meninges]].<ref name="Maton">{{cite book| last = Maton| first = Anthea| author2 = Jean Hopkins| author3 = Charles William McLaughlin| author4 = Susan Johnson| author5 = Maryanna Quon Warner| author6 = David LaHart| author7 = Jill D. Wright| title = Human Biology and Health| publisher = Prentice Hall| year = 1993| location = Englewood Cliffs, New Jersey, US| pages = [https://archive.org/details/humanbiologyheal00scho/page/132 132–144]| isbn = 0-13-981176-1| url-access = registration| url = https://archive.org/details/humanbiologyheal00scho/page/132}}</ref> The meninges provide [[Blood–brain barrier|a barrier]] to chemicals dissolved in the blood, protecting the brain from most [[neurotoxins]] commonly found in food. Within the meninges the brain and spinal cord are bathed in [[cerebral spinal fluid]] which replaces the [[Extracellular fluid|body fluid]] found outside the cells of all [[bilaterian|bilateral animals]].

In vertebrates, the CNS is contained within the [[dorsal body cavity]], while the brain is housed in the [[cranial cavity]] within the [[skull]]. The spinal cord is housed in the [[spinal canal]] within the [[vertebrae]].<ref name="Maton" /> Within the CNS, the interneuronal space is filled with a large amount of supporting non-nervous cells called neuroglia or [[glia]] from the Greek for "glue".<ref name="KettenmannFaissner1996">{{cite book|last1=Kettenmann|first1=H.|last2=Faissner|first2=A.|last3=Trotter|first3=J.|title=Comprehensive Human Physiology|chapter=Neuron-Glia Interactions in Homeostasis and Degeneration|year=1996|pages=533–543|doi=10.1007/978-3-642-60946-6_27|isbn=978-3-642-64619-5}}</ref>

In vertebrates, the CNS also includes the [[retina]]<ref name="Purves 2000">{{cite book | last1 = Purves | first1 = Dale | title = Neuroscience, Second Edition | year = 2000 | url = https://www.ncbi.nlm.nih.gov/books/NBK10799/ | isbn = 9780878937424 | location = Sunderland, MA | publisher = Sinauer Associates | url-status = live | archive-url = https://web.archive.org/web/20140311185033/http://www.ncbi.nlm.nih.gov/books/NBK10799/ | archive-date = 11 March 2014 | df = dmy-all }}</ref> and the [[optic nerve]] ([[cranial nerve]] II),<ref>{{cite web|title=Medical Subject Headings (MeSH): Optic Nerve|url=https://www.ncbi.nlm.nih.gov/mesh/68009900|publisher=National Library of Medicine|access-date=28 September 2013|url-status=live|archive-url=https://web.archive.org/web/20131002063049/http://www.ncbi.nlm.nih.gov/mesh/68009900|archive-date=2 October 2013|df=dmy-all}}</ref><ref name="Fitzgerald" /> as well as the [[olfactory nerves]] and [[olfactory epithelium]].<ref name="Gizurarson S. 2012 566–582">{{cite journal | author = Gizurarson S | title = Anatomical and histologica\ ]=\ factors affecting intranasal drug and vaccine delivery. | journal = Current Drug Delivery | volume = 9 | issue = 6 | pages = 566–582 | year = 2012 | pmid = 22788696 | pmc = 3480721 | doi = 10.2174/156720112803529828 }}</ref> As parts of the CNS, they connect directly to brain neurons without intermediate [[ganglion|ganglia]]. The [[olfactory epithelium]] is the only central nervous tissue outside the meninges in direct contact with the environment, which opens up a pathway for [[therapeutic]] agents which cannot otherwise cross the meninges barrier.<ref name="Gizurarson S. 2012 566–582"/>