Editing Central nervous system (section)

===Evolution===
{{multiple image
| align = right
| direction = vertical
| width     = 200
| image1    = Branchiostoma lanceolatum.jpg
| alt1      = [[Lancelet]]s or ''amphioxus'' are regarded as similar to the archetypal vertebrate form, and possess to true brain.
| width1    = 200
| image2    = Haikouichthys cropped.jpg|The early vertebrate ''[[Haikouichthys]]''
| alt2      = A neuron of the CNS, myelinated by an oligodendrocyte
| width2    = 200
| image3    = Spindle diagram.jpg
| alt3      = Traditional spindle diagram of the evolution of the vertebrates at class level.
| width3    = 200
| footer            = Top: the [[lancelet]], regarded an archetypal vertebrate, lacking a true brain. Middle: an early [[vertebrate]]. Bottom: spindle diagram of the evolution of vertebrates.
| footer_align      = center
}}
{{See also|Cephalization|Archicortex}}

====Planaria====
[[Planarian]]s, members of the phylum [[Platyhelminthes]] (flatworms), have the simplest, clearly defined delineation of a nervous system into a CNS and a [[peripheral nervous system|PNS]].<ref>{{cite book
| last = Hickman
| first = Cleveland P. Jr.
|author2=Larry S. Roberts|author3=Susan L. Keen|author4=Allan Larson|author5=Helen L'Anson|author6=David J. Eisenhour
| title = Integrated Princinples of Zoology: Fourteenth Edition
| publisher = McGraw-Hill Higher Education
| year = 2008
| location = New York, NY, US
| page = 733
| isbn = 978-0-07-297004-3}}</ref><ref>{{cite book
| last = Campbell
| first = Neil A.
|author2=Jane B. Reece|author3=Lisa A. Urry|author4=Michael L. Cain|author5=Steven A. Wasserman|author6=Peter V. Minorsky|author7=Robert B. Jackson
| title = Biology: Eighth Edition
| publisher = Pearson / Benjamin Cummings
| year = 2008
| location = San Francisco, CA, US
| page = 1065
| isbn = 978-0-8053-6844-4}}</ref>
Their primitive brains, consisting of two fused anterior ganglia, and longitudinal nerve cords form the CNS. Like vertebrates, have a distinct CNS and PNS. The nerves projecting laterally from the CNS form their PNS.

A molecular study found that more than 95% of the 116 genes involved in the nervous system of planarians, which includes genes related to the CNS, also exist in humans.<ref>{{cite journal | vauthors = Mineta K, Nakazawa M, Cebria F, Ikeo K, Agata K, Gojobori T | title = Origin and evolutionary process of the CNS elucidated by comparative genomics analysis of planarian ESTs | journal = PNAS | volume = 100 | issue = 13 | pages = 7666–7671 | year = 2003 | pmid = 12802012 | pmc = 164645 | doi = 10.1073/pnas.1332513100 | bibcode = 2003PNAS..100.7666M | df = dmy-all | doi-access = free }}</ref>

====Arthropoda====
In [[arthropods]], the [[ventral nerve cord]], the [[subesophageal ganglia]] and the [[supraesophageal ganglia]] are usually seen as making up the CNS. Arthropoda, unlike vertebrates, have inhibitory [[motor neurons]] due to their small size.<ref>{{cite journal |last1=Wolf |first1=Harald |title=Inhibitory motoneurons in arthropod motor control: organisation, function, evolution |journal=Journal of Comparative Physiology A |date=2 February 2014 |volume=200 |issue=8 |pages=693–710 |pmid=24965579 |url= |publisher=Springer |doi=10.1007/s00359-014-0922-2 |pmc=4108845 |language=en |issn=1432-1351}}</ref>
{{see also|Lateral horn of insect brain}}

====Chordata====
The CNS of [[chordate]]s differs from that of other animals in being placed [[dorsal nerve cord|dorsally]] in the body, above the gut and [[notochord]]/[[Vertebral column|spine]].<ref name=Romer>Romer, A.S. (1949): ''The Vertebrate Body.'' W.B. Saunders, Philadelphia. (2nd ed. 1955; 3rd ed. 1962; 4th ed. 1970)</ref> The basic pattern of the CNS is highly conserved throughout the different species of [[vertebrate]]s and during evolution. The major trend that can be observed is towards a progressive telencephalisation: the [[telencephalon]] of reptiles is only an appendix to the large [[olfactory bulb]], while in mammals it makes up most of the volume of the CNS. In the human brain, the telencephalon covers most of the [[diencephalon]] and the entire [[mesencephalon]]. Indeed, the [[allometry|allometric]] study of brain size among different species shows a striking continuity from rats to whales, and allows us to complete the knowledge about the evolution of the CNS obtained through [[cranial endocast]]s.

=====Mammals=====
[[Mammal]]s – which appear in the fossil record after the first fishes, amphibians, and reptiles – are the only vertebrates to possess the evolutionarily recent, outermost part of the [[cerebral cortex]] (main part of the telencephalon excluding olfactory bulb) known as the [[neocortex]].<ref name=MarkFBear>{{cite book
| last = Bear
| first = Mark F.
|author2=Barry W. Connors|author3=Michael A. Paradiso
| title = Neuroscience: Exploring the Brain: Third Edition
| publisher = Lippincott Williams & Wilkins
| year = 2007
| location = Philadelphia, PA, US
| pages = 196–199
| url = https://books.google.com/books?id=75NgwLzueikC&q=neuroscience+exploring+the+brain
| isbn = 978-0-7817-6003-4}}</ref> This part of the brain is, in mammals, involved in higher thinking and further processing of all senses in the [[sensory cortex|sensory cortices]] (processing for smell was previously only done by its bulb while those for non-smell senses were only done by the [[tectum]]).<ref>Feinberg, T. E., & Mallatt, J. (2013). The evolutionary and genetic origins of consciousness in the Cambrian Period over 500 million years ago. Frontiers in psychology, 4, 667. https://doi.org/10.3389/fpsyg.2013.00667</ref> The neocortex of [[monotremes]] (the duck-billed [[platypus]] and several species of [[echidna|spiny anteater]]s) and of [[marsupials]] (such as [[kangaroo]]s, [[koala]]s, [[opossum]]s, [[wombat]]s, and [[Tasmanian devil]]s) lack the convolutions – [[gyri]] and [[sulcus (neuroanatomy)|sulci]] – found in the neocortex of most [[placental mammals]] ([[eutherians]]).<ref name=KentCarr>{{cite book
| last = Kent
| first = George C.
|author2=Robert K. Carr
| title = Comparative Anatomy of the Vertebrates: Ninth Edition
| publisher = McGraw-Hill Higher Education
| year = 2001
| location = New York, NY, US
| page = 409
| isbn = 0-07-303869-5}}</ref>
Within placental mammals, the size and complexity of the neocortex increased over time. The area of the neocortex of mice is only about 1/100 that of monkeys, and that of monkeys is only about 1/10 that of humans.<ref name=MarkFBear/> In addition, rats lack convolutions in their neocortex (possibly also because rats are small mammals), whereas cats have a moderate degree of convolutions, and humans have quite extensive convolutions.<ref name=MarkFBear/> Extreme convolution of the neocortex is found in [[dolphin]]s, possibly related to their complex [[Animal echolocation|echolocation]].