Kwakwalwa
Kwakwalwa wata gaba ce da ke aiki a matsayin cibiyar jijiyoyi a cikin dukkan gabobin kashin baya da kuma mafi yawan invertebrate . Yana cikin kai ne, yawanci kusa da gabobin ji don ma'ana kamar hangen nesa . Ita ce mafi hadadden gaba a jikin kashin baya. A jikin ɗan adam, ƙwakwalwa ta ƙunshi kusan 14-16 biliyan neurons,  kuma kiyasin adadin neurons a cikin cerebellum shine 55-70 biliyan.  Kowane neuron yana haɗe ta hanyar synapses zuwa wasu dubunnan jijiyoyi. Waɗannan jijiyoyi yawanci suna sadarwa da juna ta hanyar dogayen zaruruwa da ake kira axon, waɗanda ke ɗaukar sadarwa na bugun sigina da ake kira ƙarfin aiki zuwa sassa mai nisa na kwakwalwa ko jikin da ke Shirin amsar kwayar halitta.

A ilimin halittar jiki, kwakwalwa suna aiwatar da iko a kan sauran gabobin jiki. Suna aiki akan sauran jikin duka ta hanyar samar da tsarin aikin tsoka da kuma ta hanyar fitar da sinadarai da ake kira hormones . Wannan sarrafawa ta tsakiya yana ba da damar saurin amsawa da haɗin kai ga canje-canje a cikin yanayi . Wasu nau'ikan amsawa na asali kamar reflexes za a iya yin sulhu ta hanyar kashin baya ko ganglia na gefe, amma ƙayyadaddun ikon sarrafa ɗabi'a bisa haɗaɗɗiyar shigarwar azanci yana buƙatar bayanin haɗa ƙarfin kwakwalwa ta tsakiya.

Yanzu ana fahimtar ayyukan kwayar halitta guda ɗaya daki-daki amma har yanzu ba a warware yadda suke haɗa kai cikin tarin miliyoyin mutane ba.  Samfuran na baya-bayan nan a cikin ilimin kimiyyar jijiya na zamani suna ɗaukar kwakwalwa a matsayin kwamfuta ta halitta, wadda ta bambanta da na'ura mai kwakwalwa da kwamfuta, amma kamanceceniya ta yadda tana samun bayanai daga kewayen duniya, tana adana ta, da sarrafa ta ta hanyoyi daban-daban.

Wannan makalan yana auna ayyukan kwakwalwa a cikin dukkan nau'ikan dabbobi, tare da kulawa mafi girma ga kashin baya. Yana mu'amala da kwakwalwar dan adam gwargwadon yadda yake raba abubuwan da sauran kwakwalwar suke. Hanyoyin da kwakwalwar dan adam ta bambanta da sauran kwakwalwa an rufe su a cikin labarin kwakwalwar mutum. Batutuwa da dama da za a iya rufe su a maimakon haka an rufe su a can domin ana iya faɗi da yawa game da su a cikin mahallin ɗan adam. Muhimman abubuwan da ke cikin labarin kwakwalwar ɗan adam sune cututtukan kwakwalwa da illar lalacewar kwakwalwa .

Siffa da girman kwakwalwa sun bambanta sosai tsakanin nau'in jinsi, kuma gano abubuwan gama gari sau da yawa yana da wahala.  Duk da haka, akwai wasu ƙa'idodi na gine-ginen kwakwalwa waɗanda ke aiki a cikin nau'in nau'in ka'idoji da tsarin gine-ginen da ke cikin tsarin gine-ginen kwakwalwa da suka shafi tsarin gine-ginen kwakwalwa da ke amfani da tsarin kwakwalwa da suka shafi aikin kwakwalwa da yawa.  Wasu sassa na tsarin kwakwalwa sun zama gama gari ga kusan dukkanin nau'ikan dabbobi;  wasu sun bambanta da kwakwalwar ''ci-gaba'' daga wadanda suka fi dadewa, ko kuma suka banbance kashin baya da na baya. 

Hanya mafi sauƙi don samun bayanai game da ilimin halittar kwakwalwa ita ce ta duban gani, amma an ƙirƙiri wasu fasahohi masu yawa. Naman kwakwalwa a cikin yanayinsa yana da taushi sosai don yin aiki da shi, amma ana iya daure shi ta hanyar nutsewa a cikin barasa ko wasu abubuwan gyarawa, sannan a yanka shi don nazarin ciki. A gani, cikin kwakwalwa ya ƙunshi yankuna abin da ake kira launin toka, tare da launi mai duhu, rabu da yankunan fararen fata, tare da launi mai haske. Ana iya samun ƙarin bayani ta hanyar ɓata sassan nama na kwakwalwa tare da sinadarai iri-iri waɗanda ke fitar da wuraren da takamaiman nau'ikan ƙwayoyin cuta ke cikin yawa. Hakanan yana yiwuwa a bincika ƙananan ƙwayoyin nama na kwakwalwa ta amfani da na'urar hangen nesa, da kuma gano tsarin haɗin kai daga wannan yanki na kwakwalwa zuwa wani.

Tsarin Kwayar Halitta 

Ƙwaƙwalwar kowane nau'in nau'in nau'i ne na farko da ya ƙunshi nau'i-nau'i masu yawa na sel guda biyu: neurons da glial cells . Kwayoyin Glial (wanda aka fi sani da glia ko neuroglia ) sun zo cikin nau'i-nau'i da yawa, kuma suna yin ayyuka masu mahimmanci, ciki har da goyon bayan tsari, goyon bayan rayuwa, rufi, da jagorancin ci gaba. Neurons, duk da haka, yawanci ana ɗaukar su ne mafi mahimmancin sel a cikin kwakwalwa.  Abubuwan da ke sa neurons su zama na musamman shine ikon su na aika sigina zuwa takamaiman sel masu nisa a nesa mai nisa.  Suna aika waɗannan sako ta hanyar axon, wanda shine siraran protoplasmic fiber wanda ke fitowa daga jikin tantanin halitta kuma yana aiwatarwa, yawanci tare da rassa masu yawa, zuwa wasu wurare, wani lokacin kusa, wani lokacin a cikin sassan kwakwalwa ko jiki masu nisa. Tsawon axon na iya zama na ban mamaki: alal misali, idan kwayar pyramidal (wani abu mai ban sha'awa) na kwakwalwar kwakwalwa ya girma ta yadda jikin tantanin halitta ya zama girman jikin mutum, axon, daidai da girma, zai zama igiya. 'yan santimita a diamita, wanda ya wuce fiye da kilomita.  Waɗannan axon suna watsa sigina a cikin nau'in bugun jini na lantarki da ake kira ƙarfin aiki, wanda bai wuce kashi dubu ɗaya na daƙiƙa ba kuma yana tafiya tare da axon a cikin gudun mita 1-100 a cikin daƙiƙa guda. Wasu neurons suna fitar da yuwuwar aiki akai-akai, akan ƙimar 10-100 a sakan daya, yawanci a cikin tsarin da ba na ka'ida ba; sauran jijiyoyi suna shuru mafi yawan lokaci, amma lokaci-lokaci suna fitar da fashewar damar aiki. 

Axon suna watsa sigina zuwa wasu ƙananan ƙwayoyin cuta ta hanyar haɗin gwiwa na musamman da ake kira synapses . Axon guda ɗaya na iya yin haɗin kai har dubu da yawa tare da wasu kwayoyin halitta  Lokacin da yuwuwar aiki, tafiya tare da axon, ya isa wurin synapse, yana haifar da sakin sinadari da ake kira neurotransmitter . Neurotransmitter yana ɗaure ga ƙwayoyin mai karɓa a cikin membrane na kwayar da aka yi niyya. 

Synapses sune mahimman abubuwan aikin kwakwalwa.  Muhimmancin aikin kwakwalwa shine sadarwar salula zuwa tantanin halitta, kuma synapses sune wuraren da sadarwa ke faruwa. An kiyasta kwakwalwar dan adam tana dauke da kusan tiriliyan 100 synapses;  hatta kwakwalwar kuda ta 'ya'yan itace tana dauke da miliyan dayawa.  Ayyukan waɗannan synapses sun bambanta sosai: wasu suna da ban sha'awa (mai ban sha'awa na kwayar halitta); wasu kuma masu hanawa; wasu suna aiki ta hanyar kunna tsarin manzo na biyu waɗanda ke canza sinadarai na ciki na sel masu manufa ta hanyoyi masu rikitarwa.  Babban adadin synapses ana iya canza su sosai; wato suna iya canza ƙarfi ta hanyar da tsarin siginar da ke ratsa su ke sarrafa su. An yi imani da cewa gyare-gyaren da ya dogara da ayyuka na synapses shine tsarin farko na kwakwalwa don koyo da ƙwaƙwalwa. 

Yawancin sarari a cikin kwakwalwa ana ɗaukar su ta hanyar axon, waɗanda galibi ana haɗa su tare a cikin abin da ake kira hanyoyin fiber jijiya . An nannade wani axon mai myelin a cikin wani kumfa mai rufe fuska na myelin, wanda ke taimakawa sosai wajen haɓaka saurin yaɗa sigina. (Akwai kuma axon marasa lafiya). Myelin fari ne, yana sa sassan kwakwalwa da ke cike da filaye na jijiyoyi suna bayyana a matsayin fararen fata mai launin haske, sabanin launin toka mai duhu wanda ke nuna wuraren da ke da yawa na jikin kwayoyin neuron.

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