Základní pojmy
Nervy (4 fotografie)
Thefiberterminalpartoftheperipheralnerveterminatesintheuniquestructureformedinothertissues,Callednerveending(nerveending).Accordingtotheirfunctions,nerveendingscanbedividedintotwocategories:sensorynerveendingsandmotornerveendings.Senzorické nervové vývody - prstencové tělíska, oválný tvar, vnitřní hřídel, senzorická nervová vlákna, pláště.
Motornerveendings-motorendplates,myelinatednervefibersbranchrepeatedlytoskeletalmusclebundlesandextendtomusclefibers.Nervefibersapproachthesarcolemmaandbranchrepeatedly,withabutton-likeend.Thisiscalledthemotorendplate
Funkce
Pocit
Aspecificstructureformedbytheterminalpartoftheprocesssurroundingasensory(afferent)neuronandothertissuestructuresiscalledareceptor.Itcanfeelvariousstimuliinsideandoutsidethehumanbody,andtransformitintonerveimpulses,whicharetransmittedtothecenter.Sensorynerveendingscanbedividedintofreenerveendingsandtunicatesensorynerveendingsaccordingtotheirstructure.
Volný, uvolnit
(freenerveending)Thiskindofterminaliswidelydistributedintheepidermis,cornea,serosalmembrane,muscleandconnectivetissue,andthestructureisrelativelysimple.Themyelinsheathoftheperipheralprocessdisappearsneartheterminalend,anditsexposedfinebranchesbranchrepeatedly,anddispersefreelyacrossepithelialcellsorconnectivetissues,andcanfeelthestimulationofpainandcoldandheat.
Pohyb
Motornerveending(motornerveending)istheendoftheefferentnervefiberofthemotorneuron
,endinginSkeletalmuscle,myocardium,smoothmuscleandglandsformeffectors,whichinnervatemusclecontractionorglandularsecretion.Therearetwotypesofefferentnervefibers:oneisthesomaticefferentnervefiberwithmyelinsheath,whichisacomponentoftheperipheralnerve,anditsendformsthemotorendplateintheskeletalmusclefiber;theotheristhevisceralefferentnervefiber,Nomyelinsheath,sentoutfromtheautonomicganglion,endinginthemyocardium,smoothmuscleandglandularepithelium,thenerveendingsareswollennodules.
Klasifikace
Tam jsou sladěny senzorické nervy
(encapsulatenerveendig)Therearemanyformsofthiskindofsensorynerveendig,andthesizeisdifferent.One,butthenerveendingsarecoveredwithconnectivetissuecapsules.Thecommononesare:
(1)Tactilecorpuscle:alsoknownasMeissnercorpuscle,distributedinInthedermalpapillaoftheskin,thepalmsofthefingersandtheundersidesofthetoesarethemostcommon.Thecorpuscleiselliptical,withadiameterofabout30-100μm,surroundedbyconnectivetissuetoformacapsule,andtherearemanyrowsofflattactilecells.Myelinatednervefiberslosemyelinsheathatthetunicateandpenetrateintothetunicate,andthebranchesarecoiled.Themainfunctionistofeelthesenseoftouch.
(2)Lamellarcorpuscle:alsoknownasPaciniancorpuscle,thistypeofcorpuscleiswidelydistributed,morecommoninthedeepdermis,subcutaneoustissue,mesentericandpancreasConnectivetissue.Thecorpusclesaremostlyroundorelliptical,withdifferentsizesandadiameterofabout0.5-3mm.Thecapsuleofthecorpuscleisaconcentriclamellaformedbyflatconnectivetissuecellsandfibers,andthelamellaisfilledwithgel-likesubstances.Thecentralaxisofthecorpuscleisahomogeneouscylinder.Itissaidthattheinnerbulbnervefiberlosesmyelinandenterstheinnerbulb,mainlyforfeelingpressure,vibrationandtension.
(3)Musclespindle:Aslenderspindle-shapedbodywidelydistributedintheskeletalmusclesofthewholebody,about2～5mminlength,withaconnectivetissuecapsuleonthesurface,whichcontains3～10thinnerskeletalmusclefibersarecalledintrafusalmusclefibers.Therearetwotypesofsensorynervefibersthatenterthemusclespindle:onesensorynervefiberisathickmyelinatednervefiber.Thehumanmusclespindlelosesmyelinsheathinfrontofthemusclespindle,andentersthemusclespindleinthemiddleofthemusclespindle.Itwrapsaroundthenucleus-containingpartoftheinnerspindlemuscle;theotherisathinmyelinatednervefiber,whichhasaflowerbranchshapeafterlosingmyelinsheath,andisdistributedatbothendsofthenerveterminal.Inaddition,thereisathinmotornervefiberinthemusclespindle,whichcomesfromthesmallneuron(γneuron)intheanteriorhornofthespinalcord.Themusclespindleislocatedbetweenthemusclefiberbundles.Whenthemusclecontractsorstretches,theinnerspindlemusclefibersareforcedtostimulatethenerveendingsandgeneratenerveimpulses,whicharetransmittedtothecentertoproducesensations.Therefore,themusclespindlesarethemainbodythatsensesthemovementofmusclesandchangesinthepositionofthelimbs.Receptors.Thestructureoftendonspindleissimilartothatofmusclespindle.
Motorendplateneuronterminál
(motorendplate)ItcomesfromtheaxonterminalofthemotorneuronintheanteriorhornofthespinalcordorbrainstemandreachesThemusclemembraneofskeletalmusclefiberslosesmyelinsheath,andthendividesintoclaw-shapedfinebranches.Theterminalswellsandformsanellipticalplate-shapedbulgeonthesurfaceoftheskeletalmusclefiber,withadiameterof10to80μm.Mitochondriaandsphericalsynapticvesiclesinthesphericalterminaloftheaxoncontainacetylcholine.Theaxonmembraneofthesphericalterminalisthepresynapticmembrane,andthemusclemembranecorrespondingtotheanteriormembraneisthepostsynapticmembrane.ThereareNreceptorsinthemembrane.Thesurfaceareaoftherearmembrane.Betweenthepre-synapticandposteriormembranesisasynapticgapwithawidthofabout40-60nm.Itcanbeseenthatthemotorendplateisaneuromuscularjunction(neuromuscularjunction).AcetylcholinereleasedbysynapticvesiclesactsontheNreceptorsofthepostsynapticmembrane.Itcausesthemusclemembranetobeexcitedandisconductedtotheentiremusclefiberthroughthetransversetubulesystem,causingthemusclefibertocontract.Eachbranchofprefilledmotorneuronaxoncaninnervate100to2000skeletalmusclefibers.
Themusclefibersinnervatedbytheaxonanditsbranchesofeachmotorneuronarecalledamotorunit.Thesizeofthemotorunitisthenumberoffiberlinesinnervatedbythemotorneuron.Thereisabigdifferenceinthenumberofmotorunitsofeachmuscleinthehumanbody.Usuallythenumberofmotorunitsoflimbmusclesislarge;themotorunitsofsmallmusclessuchashandsandfeetarefew.Forexample,thehumantibialisanteriormusclehas443motorunits,andthenumberofmusclefiberspermotorunitis562.Thevermiformmuscleofthehandhasonly96motorunits,andthenumberofmusclefibersineachmotorunitis108.Muscleatrophyoccurswhenfronthornmotorneurondiseaseorperipheralnerveinjuryoccurs,whichwillinvolvechangesinthenumberofvarioustypesofmusclefibersandeachsportsshoeunit.
Viscerální motorické nervy
(visceralmotornerveending)Thevisceralmotornerveendingisinnervatedbyautonomicneurons,usuallypassingthroughtwoneurons,passingthroughAutonomicganglia.Thefirstneuroniscalledthepreganglionicneuron,thecellbodyislocatedinthelateralgraymatterhornofthespinalcordorthebrainstemnucleus,anditsaxoniscalledthepreganglionicfiber;thesecondneuroniscalledthepostganglionicneuron,andthecellbodyislocatedintheautonomicganglionornerveplexusInside,itsaxonsarecalledpostganglionicfibers.Thesepostganglionicnervefibersaredistributedonthesmoothmuscle,myocardiumandglandcellsofthevisceraandbloodvessels,formingvisceralmotornerveendings.Thesevisceralefferentfibersaremostlyunmyelinatednervefibers,withverythinaxons,withadiameteroflessthan1μm.Theaxonterminalstructureissimple.Afterrepeatedbranching,theterminalbranchisenlargedinabeadedshape.Theenlargedterminalpartiscalledthenerveendingnodule,whichisattachedtosmoothmusclecellsorglandcells.Theterminalbranchisabeadedenlargedpart,calledvaricosity,withadiameterof1to2μm.Thebulgeisthepartthatestablishesasynapsewiththeeffectorcell.Theaxonofanautonomicneurondoesnotbranchattheendcanformabout30,000bulges.Thisstructureincreasestheareaorsurfaceareawhereneuronsreleaseneurotransmitters.Undertheelectronmicroscope,itcanbeseenthattherearemanysynapticcisternsandmitochondriainthebulge.Theexpandedaxonmembraneisthepresynapticmembrane,andthecorrespondingeffectorcellmembraneisthepostsynapticmembrane,withneurotransmitterreceptorsonthemembrane.Thesynapticcleftis15-20nm.Thegapbetweensomebulgingandeffectorcellsisabove80nm,evenuptoseveralmicrometers.Thecorrespondingpartdoesnothavethespecializedstructureofpostsynapticmembrane.Therefore,thisformofsynapseiscalleddistantsynapse(distantsynapse).synapse)ornon-synapticchemicaltransmission(non-synapticchemicaltransmission),whichproduceseffectsintheformofdispersion.Themaintransmittersofautonomicneuronsareacetylcholine,norepinephrineandpeptides.Whennerveexcitementspreadsnervefibersalongthevisceratotheends,itleadstothereleaseofneurotransmitters,causingsmoothmuscleandcardiacmusclecontractionandglandularsecretion.