Editing Octopus (section)

===Nervous system and senses===
Octopuses and their relatives have a more expansive and complex [[nervous system]] than other invertebrates, containing over 500 million [[neuron]]s, around the same as a dog.<ref name="Albertin Simakov 2015"/><ref>{{cite journal | last1=Chung | first1=Wen-Sung | last2=Kurniawan | first2=Nyoman D. | last3=Marshall | first3=N. Justin | title=Comparative brain structure and visual processing in octopus from different habitats | journal=Current Biology | volume=32 | issue=1 | date=2022-01-10 | issn=1879-0445 | pmid=34798049 | doi=10.1016/j.cub.2021.10.070 | pages=97–110.e4| bibcode=2022CBio...32E..97C | doi-access=free }}</ref><ref>{{cite book |last=Budelmann |first=B. U. |year=1995 |chapter-url={{google books|plainurl=y|id=dW5e6FHOH-4C|page=PA115}} |chapter=The cephalopod nervous system: What evolution has made of the molluscan design |editor-last1=Breidbach |editor-first1=O. |editor-last2=Kutsch |editor-first2=W. |title=The nervous systems of invertebrates: An evolutionary and comparative approach |publisher=Birkhäuser |isbn=978-3-7643-5076-5 |lccn=94035125}}</ref> One part is localised in the brain, contained in a cartilaginous capsule. Two-thirds of the neurons are in the nerve cords of its arms. This allows their arms to perform actions with a degree of independence.<ref>{{cite journal |last=Hochner |first=B. |year=2012 |title=An Embodied View of Octopus Neurobiology |journal=Current Biology |volume=22 |issue=20 |pages=R887–R892 |doi=10.1016/j.cub.2012.09.001 |pmid=23098601 |doi-access=free|bibcode=2012CBio...22.R887H }}</ref> Learning mainly occurs in the brain, while arms make decisions independently when supplied with information.<ref>{{cite journal|last1=Gutnick|first1=T|last2=Zullo|first2=L|last3=Hochner|first3=B|last4=Kuba|first4=M. J.|year=2020|title=Use of peripheral sensory information for central nervous control of arm movement by Octopus|journal=Current Biology|volume=30|issue=21|pages=4322–4327|doi=10.1016/j.cub.2020.08.037|pmid=32916119}}</ref> A severed arm can still move and respond to stimuli.<ref>{{cite journal|last1=Hague|first1=T|last2=Florini|first2=M|last3=Andrews|first3=P. L. R.|year=2013|title=Preliminary in vitro functional evidence for reflex responses to noxious stimuli in the arms of ''Octopus vulgaris''|journal=Journal of Experimental Marine Biology and Ecology|volume=447|pages=100–105|doi=10.1016/j.jembe.2013.02.016|bibcode=2013JEMBE.447..100H}}</ref> Unlike in many other animals, including other mollusks, the movement of octopuses and their relatives are not organised in their brains via internal [[somatotopic arrangement|somatotopic map]]s of their bodies.<ref>{{cite journal |pmid=19765993 |doi=10.1016/j.cub.2009.07.067 |volume=19 |issue=19 |title=Nonsomatotopic organization of the higher motor centers in Octopus |first1=L. |last1=Zullo |first2=G. |last2=Sumbre |first3=C. |last3=Agnisola |first4=T. |last4=Flash |first5=B. |last5=Hochner |year=2009 |pages=1632–1636 |journal=Current Biology |s2cid=15852956 |doi-access=free |bibcode=2009CBio...19.1632Z }}</ref> Octopuses have the same [[jumping genes]] that are active in the human brain, implying an [[evolutionary convergence]] at molecular level.<ref name="Petrosino Ponte Volpe 2022">{{cite journal | last1=Petrosino | first1=Giuseppe | last2=Ponte | first2=Giovanna | last3=Volpe | first3=Massimiliano | last4=Zarrella | first4=Ilaria | last5=Ansaloni | first5=Federico | last6=Langella | first6=Concetta | last7=Di Cristina | first7=Giulia | last8=Finaurini | first8=Sara | last9=Russo | first9=Monia T. | last10=Basu | first10=Swaraj | last11=Musacchia | first11=Francesco | last12=Ristoratore | first12=Filomena | last13=Pavlinic | first13=Dinko | last14=Benes | first14=Vladimir | last15=Ferrante | first15=Maria I. | last16=Albertin | first16=Caroline | last17=Simakov | first17=Oleg | last18=Gustincich | first18=Stefano | last19=Fiorito | first19=Graziano | last20=Sanges | first20=Remo |display-authors=3 | title=Identification of LINE retrotransposons and long non-coding RNAs expressed in the octopus brain | journal=BMC Biology | volume=20 | issue=1 | date=18 May 2022 | page=116 | doi=10.1186/s12915-022-01303-5 | pmid=35581640 | pmc=9115989 | s2cid=231777147 | doi-access=free }}</ref>

[[File:Reef1072 - Flickr - NOAA Photo Library.jpg|thumb|left|Eye of [[common octopus]]|alt=Close up of an octopus showing its eye and an arm with suckers]]

Like other cephalopods, octopuses have camera-like eyes.<ref name="Albertin Simakov 2015"/> [[Colour vision]] appears to vary from species to species, for example, it is present in ''[[Amphioctopus aegina|A. aegina]]'' but absent in ''[[Common octopus|O. vulgaris]]''.<ref>{{cite journal |last1=Kawamura |first1=G. |year=2001 |title=Color Discrimination Conditioning in Two Octopus ''Octopus aegina'' and ''O. vulgaris'' |journal=Nippon Suisan Gakkaishi |volume=67 |issue=1 |pages=35–39 |doi=10.2331/suisan.67.35 |display-authors=etal |df=dmy-all |doi-access=free }}</ref> [[Opsin]]s in the skin respond to different wavelengths of light and help the animals choose a colouration that matches the surroundings and camouflages them; [[chromatophores]] in the skin can respond to light independently of the eyes.<ref name="Kingston Kuzirian 2015">{{cite journal |last1=Kingston |first1=Alexandra C. N. |last2=Kuzirian |first2=Alan M. |last3=Hanlon |first3=Roger T. |last4=Cronin |first4=Thomas W. |title=Visual phototransduction components in cephalopod chromatophores suggest dermal photoreception |journal=Journal of Experimental Biology |volume=218 |issue=10 |year=2015 |pages=1596–1602 |issn=1477-9145 |doi=10.1242/jeb.117945|pmid=25994635 |doi-access=free |bibcode=2015JExpB.218.1596K |hdl=11603/13387 |hdl-access=free }}</ref><ref name="Ramirez Oakley 2015">{{cite journal |last1=Ramirez |first1=M. Desmond |last2=Oakley |first2=Todd H. |title=Eye-independent, light-activated chromatophore expansion (LACE) and expression of phototransduction genes in the skin of Octopus bimaculoides |journal=Journal of Experimental Biology |volume=218 |issue=10 |year=2015 |pages=1513–1520 |issn=1477-9145 |doi=10.1242/jeb.110908|pmid=25994633 |pmc=4448664 |doi-access=free |bibcode=2015JExpB.218.1513R }}</ref> An alternative hypothesis<!--Stubbs et al--> is that [[cephalopod eye]]s in species that only have a single [[photoreceptor protein]] may use [[chromatic aberration]] to turn monochromatic vision into colour vision, though this lowers image quality. This would explain pupils shaped like the letter "U", the letter "W", or a [[dumbbell]], as well as the need for colourful mating displays.<ref name="StubbsStubbs2016">{{cite journal |last1=Stubbs |first1=Alexander L. |last2=Stubbs |first2=Christopher W. |title=Spectral discrimination in color blind animals via chromatic aberration and pupil shape |journal=Proceedings of the National Academy of Sciences |volume=113 |issue=29 |year=2016 |pages=8206–8211 |issn=0027-8424 |doi=10.1073/pnas.1524578113|pmid=27382180 |pmc=4961147 |bibcode=2016PNAS..113.8206S |doi-access=free }}</ref>

Attached to the optic capsules are two organs called [[statocyst]]s (sac-like structures containing a mineralised mass and sensitive hairs), that allow the octopus to sense the orientation of its body, relative to both gravity and time ([[angular acceleration]]). An [[autonomic nervous system|autonomic]] response keeps the octopus's eyes oriented so that the pupil is always horizontal.<ref name=Ruppert/>{{rp|360–361}} Octopuses may also use the statocyst to hear. The common octopus can hear sounds between 400&nbsp;Hz and 1000&nbsp;Hz, and hears best at 600&nbsp;Hz.<ref name="HuYan2009">{{cite journal |last1=Hu |first1=Marian Y. |last2=Yan |first2=Hong Young |last3=Chung |first3=Wen-Sung |last4=Shiao |first4=Jen-Chieh |last5=Hwang |first5=Pung-Pung |title=Acoustically evoked potentials in two cephalopods inferred using the auditory brainstem response (ABR) approach |journal=Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology |volume=153 |issue=3 |year=2009 |pages=278–283 |issn=1095-6433 |doi=10.1016/j.cbpa.2009.02.040 <!--|url=https://www.ecovis.org.au/wp-content/uploads/2015/04/squid-hearing.pdf--> |pmid=19275944 |url=http://ntur.lib.ntu.edu.tw//handle/246246/162905 |access-date=13 March 2022 |archive-date=7 April 2022 |archive-url=https://web.archive.org/web/20220407151928/http://ntur.lib.ntu.edu.tw//handle/246246/162905 |url-status=dead }}</ref>

Octopuses have an excellent [[somatosensory system]]. Their suction cups are equipped with [[chemoreceptors]] so they can [[taste]] what they touch.<ref>{{cite journal|last1=van Giesen|first1=L|last2=Kilian|first2=P. B.|last3=Allard|first3=C. A. H.|last4=Bellon|first4=N. W.|year=2020|title=Molecular basis of chemotactile sensation in Octopus|journal=Cell|volume=183|issue=3|pages=594–604|doi=10.1016/j.cell.2020.09.008|pmid=33125889|pmc=7605239}}</ref> Octopus arms move easily because the sensors recognise octopus skin and prevent self-attachment.<ref name="Nesher Levy Grasso Hochner 2014">{{cite journal |last1=Nesher |first1=Nir |last2=Levy |first2=Guy |last3=Grasso |first3=Frank W. |last4=Hochner |first4=Binyamin |title=Self-Recognition Mechanism between Skin and Suckers Prevents Octopus Arms from Interfering with Each Other |journal=Current Biology |volume=24 |issue=11 |year=2014 |issn=0960-9822 |doi=10.1016/j.cub.2014.04.024 |pages=1271–1275|pmid=24835454 |s2cid=16140159 |doi-access=free |bibcode=2014CBio...24.1271N }}</ref> Octopuses appear to have poor [[proprioception|proprioceptive]] sense and must see their arms to keep track of their position.<ref>{{cite journal|last1=Gutnick|first1=Tamar|last2=Byrne|first2=Ruth A.|last3=Hochner|first3=Binyamin|last4=Kuba|first4=Michael|year=2011|title=''Octopus vulgaris'' Uses Visual Information to Determine the Location of Its Arm|journal=Current Biology|volume=21|issue=6|pages=460–462|doi=10.1016/j.cub.2011.01.052|pmid=21396818|s2cid=10152089|doi-access=free|bibcode=2011CBio...21..460G }}</ref><ref>{{cite journal|last1=Kennedy|first1=E. B. Lane|last2=Buresch|first2=Kendra C.|last3=Boinapally|first3=Preethi|last4=Hanlon|first4=Roger T.|year=2020|title=Octopus arms exhibit exceptional flexibility|journal=Scientific Reports|volume=10|issue=1|page=20872|doi=10.1038/s41598-020-77873-7|pmid=33257824|pmc=7704652}}</ref>