Isakhiwo kanye Nomsebenzi Wamaseli eSchwann
Amaseli e-Schwann awuhlobo lweseli le-glial (iseli elisekelayo) elitholakala ohlelweni lwezinzwa oluseceleni (i-PNS). Indima yawo eyinhloko ibalulekile ngoba anesibopho sokwakheka kwe-myelin, ukuvikelwa kwe-axon, kanye nokusiza ekulungisweni kwezinzwa ngemva kokulimala. Ngaphandle kwamaseli e-Schwann, imizwa yezinzwa ayikwazi ukuhamba kahle nangokushesha njengoba umzimba udinga ukuhlanganisa ukunyakaza, imizwa, kanye nemisebenzi ehlukahlukene yezitho. Lesi sihloko sixoxa ngesakhiwo samaseli e-Schwann, indlela asebenza ngayo, kanye nemisebenzi eyinhloko ewenza abaluleke empilweni yezinzwa.
Incazelo kanye nendawo yamaseli eSchwann ohlelweni lwezinzwa
Esimisweni sezinzwa, amaseli e-glial asebenza "njengeqembu lokusekela" lama-neurons. Esimisweni sezinzwa esiphakathi (i-CNS), njengobuchopho kanye nentambo yomgogodla, i-myelin yakhiwa ama-oligodendrocyte. Okwamanje, ohlelweni lwezinzwa oluseceleni, lo mthwalo wemfanelo uwela kumaseli e-Schwann. Amaseli e-Schwann anamathela kuma-axon e-neuronal futhi, ngezindlela ezithile, awamboze, akhe ungqimba lwe-myelin noma olunye uhlaka oluvikelayo, kuye ngohlobo lwe-axon alusebenzisayo.
Amaseli e-Schwann angatholakala cishe kuzo zonke izinzwa ezingaphandle, okuhlanganisa izinzwa ezizwayo (ezithwala ulwazi oluvela kuma-receptors oluya ebuchosheni), izinzwa ezishukumisayo (ezithwala imiyalo esuka ebuchosheni iya emisipheni), kanye nezinzwa ezizimele (ezilawula izitho zangaphakathi ngaphandle kokuqaphela okuqaphelayo).
Isakhiwo esiyisisekelo samaseli eSchwann
Ngokuvamile, amaseli eSchwann anesakhiwo esivumelaniswe nendima yawo njengesimbozo kanye nokusekela ama-axon. Ezinye zezingxenye zawo ezibalulekile zifaka:
1. Umzimba weseli kanye ne-nucleus yeseli
Amaseli eSchwann anama-nuclei avame ukutholakala emngceleni weseli, ikakhulukazi lapho iseli lakha i-myelin. Lesi sikhundla "somphetho" se-nucleus sihlobene nama-coil amaningi e-membrane akha i-myelin kwezinye izindawo.
2. Ulwelwesi lweplasma oluzungeze i-axon
Isici esiyinhloko samaseli eSchwann yikhono lawo lokugoqa ama-axon. I-plasma membrane yawo igoqa ngokuphindaphindiwe i-axon ukuze yakhe ungqimba olunezingqimba eziningi, olucebile ngamafutha. Lolu ngqimba lubizwa ngokuthi i-myelin sheath, esebenza njengesivikelo sikagesi.
3. I-Cytoskeleton kanye nezingxenye zangaphakathi
Njengamanye amaseli, amaseli eSchwann ane-cytoplasm ene-organelles (i-mitochondria, i-endoplasmic reticulum, i-Golgi apparatus) ukukhiqiza amandla nokulawula ukukhiqizwa kwamaprotheni. Amaprotheni athile abalulekile ekuzinzeni kwe-myelin kanye nokuxhumana nama-axon.
4. I-basal lamina (i-basal lamina)
Esinye isici esibalulekile samaseli eSchwann ukuba khona kwe-basal lamina ezungeze amaseli. Lolu ngqimba ludlala indima ekusekelweni kwesakhiwo, luhlinzeka ngokunamathela kweseli, futhi lubalulekile ekuvuseleleni imizwa ngemva kokulimala. I-basal lamina ingasebenza "njengomzila" noma umzila, isize ukukhula kabusha kwe-axon.
Izinhlobo zamaseli eSchwann ngokusekelwe emsebenzini
Amaseli e-Schwann awakhi njalo i-myelin. Kunezigaba ezimbili eziyinhloko:
1. Amaseli e-Schwann ahlukanisa i-myelin (amaseli e-Schwann ahlukanisa i-myelin)
I-myelin yeseli elilodwa le-Schwann ivame ukugoqa ingxenye eyodwa ye-axon. Lokhu kuhlukaniswa kudala izikhala ezincane phakathi kwama-sheath e-myelin abizwa ngokuthi ama-node e-Ranvier. Ama-node e-Ranvier abalulekile ekudlulisweni okusheshayo kwama-impulses nge-saltatory conduction (ama-impulses "agxuma" esuka kwenye i-node aye kwenye).
2. Amaseli e-Schwann angabophisi i-myelin (amaseli e-Schwann angabophisi i-myelin)
Kuma-axon amancane, amaseli e-Schwann awakhi i-myelin ejiyile, kodwa kunalokho ahlanganisa ama-axon amaningana ndawonye "ngama-bundle" abizwa ngokuthi ama-Remak bundles. Nakuba engakafakwa i-myelin, amaseli e-Schwann asanikeza ukwesekwa nokuvikelwa kwe-metabolic.
Isakhiwo se-Myelin kanye nama-node e-Ranvier
I-myelin sheath yakhiwe ungqimba lwe-membrane olucebile ngama-lipid, okwenza lube yisivikelo. Lolu ngqimba lunciphisa ukuvuza kwamandla kagesi avela ku-axon futhi lusheshise ukudluliselwa kwamandla esenzo. Emizweni ye-myelin, ama-impulse awahambi njalo, kodwa kunalokho "agxuma" phakathi kwama-node e-Ranvier. Lokhu kuhanjiswa kwe-saltatory kushesha kakhulu futhi konga amandla kunokuhamba kulo lonke ulwelwesi lwe-axon.
Ngaphezu kwalokho, kunezindawo ezikhethekile ku-axon eduze kwe-node, njenge-paranode ne-juxtaparanode, ezicebile ngamaprotheni esiteshi se-ion kanye namaprotheni okunamathela. Amaseli e-Schwann adlala indima ekugcineni le nhlangano yesakhiwo esincane ukuze alondoloze izimpawu zemizwa ezizinzile.
Umsebenzi oyinhloko wamaseli eSchwann
1. Kwakha i-myelin futhi kusheshise ukudluliselwa kwe-pulse
Umsebenzi wayo owaziwa kakhulu ukwakheka kwama-myelin sheaths ezinzwa ezingaphandle. I-Myelin ikhulisa kakhulu isivinini sokudluliselwa kwe-impulse. Lokhu kuvumela ukusabela okusheshayo nokunembile kwe-motor (isb., ukuhoxisa isandla lapho sibhekene nokushisa) kanye nokucubungula imizwa (ukuzwa ukuthinta okuncane).
2. Ukuhlukaniswa nokuvikelwa kwama-axon
I-Myelin isebenza njengesivikelo sikagesi, kuyilapho amaseli e-Schwann ngokuvamile ehlinzeka ngokuvikelwa ngokomzimba kuma-axon. Lokhu kuvikelwa kwenza ama-axon amelane kakhulu nokuphazamiseka endaweni ezungezile yezicubu.
3. Ukusekelwa kwe-metabolic kwama-neurons
Ama-neuron anezidingo zamandla aphezulu, kanti ama-axon angaba made kakhulu. Amaseli e-Schwann asiza ekuqinisekiseni ukuthi ama-axon athola ukwesekwa kwe-metabolic ngokushintshana kwezakhamzimba kanye nezimpawu zama-molecule. Le ndima ibalulekile ekusindeni kwesikhathi eside komsebenzi we-axon.
4. Ukuvuselelwa kwemizwa ngemva kokulimala
Enye yezinzuzo zesistimu yezinzwa engaphandle kunesistimu yezinzwa ephakathi ukuthi inamandla okuvuselela aphakeme. Amaseli eSchwann adlala indima ebalulekile kule nqubo ngezigaba eziningana:
– Ukwehlukaniswa nokwanda: ngemva kokulimala, amaseli eSchwann azungeze indawo eyonakele ashintsha abe uhlobo olusekela ukulungiswa, bese ekhula.
– Ukuhlanza imfucumfucu ye-myelin: Amaseli e-Schwann asebenza nama-macrophage ukuhlanza imfucumfucu ye-myelin engavimbela ukuvuselelwa.
– Ukwakha “Amabhande kaBüngner”: Amaseli kaSchwann azihlela ukwakha indlela eqondisa ukukhula kabusha kwama-axons aye ezinhlosweni zawo.
– Ukukhipha izici zokukhula kwemizwa: Amaseli eSchwann akhiqiza ama-molecule afana nama-neurotrophin nezinye izici zokukhula ezikhuthaza ukunwebeka kwe-axon.
Ngaphandle kokusekelwa kwamaseli eSchwann, ukuvuselelwa kwe-axon ku-PNS bekuyoba kancane kakhulu futhi kungaqondiswa kangako.
5. Ilawula ukukhula kwemizwa nokuvuthwa kwayo
Amaseli e-Schwann nawo abalulekile kusukela ekukhuleni kombungu kuya ebudaleni. Asiza ukuvuthwa kokuxhumana kwezinzwa, anqume ukuthi yimaphi ama-axon azofakwa i-myelin, futhi alungise ukujiya kwe-myelin ngokuya ngosayizi we-axon. Lobu budlelwano buyashintshashintsha: ama-axon athumela izimpawu kumaseli e-Schwann, kanti amaseli e-Schwann anikeza impendulo ethinta ukuzinza nokusebenza kwe-axon.
6. Indima ohlelweni lokuzivikela komzimba kanye nempendulo yokuvuvukala kwendawo
Ngaphansi kwezimo ezithile, amangqamuzana eSchwann angadlala indima ekuphenduleni kwamasosha omzimba endawo. Angakhiqiza ama-molecule okubonisa izimpawu aqoqa amangqamuzana omzimba noma alawule ukuvuvukala. Lokhu kubalulekile esimweni sokulimala kwemizwa kanye nezifo.
Ukubaluleka komtholampilo: lapho amaseli eSchwann ephazamisekile
Ukulimala noma ukungasebenzi kahle kweseli likaSchwann kungaholela ku-peripheral neuropathy. Isibonelo:
– I-Guillain-Barré syndrome (GBS): isimo sokuzivikela komzimba esivame ukuhlasela i-myelin ku-PNS, okuholela ebuthakathakeni bemisipha kanye nokuphazamiseka kwezinzwa.
– I-Charcot–Marie–Tooth (CMT): iqembu lezinkinga zofuzo ezingabandakanya ukwakheka kwe-myelin okuphazamisekile noma ukusebenza kwamaseli e-Schwann, okuholela ebuthakathakeni bemisipha ekude kanye nokuphazamiseka kokuhamba.
– I-Neuroma kanye ne-schwannoma: izimila ezivela kumaseli e-Schwann, ngokuvamile azinabungozi kodwa zingacindezela izakhiwo zezinzwa futhi zibangele izimpawu.
Ukuqonda amaseli eSchwann kubalulekile ocwaningweni mayelana nezindlela zokwelapha ukuvuselelwa kwezinzwa, ubunjiniyela bezicubu, kanye nokuthuthukiswa kwemithi yezifo ezisusa i-myelin.
Isiphetho
Amaseli e-Schwann ayizingxenye ezibalulekile zesimiso sezinzwa esiseceleni. Ngokwesakhiwo, la maseli anekhono eliyingqayizivele lokumboza ama-axon, akhe i-myelin, futhi ahlinzeke nge-basal lamina, ebalulekile ekuzinzeni nasekuvuseleleni. Ngokusebenza kahle, amaseli e-Schwann asheshisa ukudluliselwa kwe-impulse ngokusebenzisa i-saltatory conduction, avikele ama-axon, asekele i-metabolism ye-neuronal, alawule ukuthuthukiswa kwezinzwa, futhi adlala indima ebalulekile ekulungisweni kwezinzwa ezisemaceleni ngemva kokulimala. Ngokuqonda isakhiwo kanye nomsebenzi wamaseli e-Schwann, singaqonda kangcono ukuthi izinzwa zisebenza kanjani nokuthi amasu ezokwelapha angathuthukiswa kanjani ukubhekana nezinkinga ezahlukene zezinzwa ezisemaceleni.
