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PhysiologyReview:NeurophysiologyPart2(BasedonGuytonsandpersonalextras)

Whatdoyouneedtoknowaboutchap.46?Theeasyway

Someofthemajorstypesofsensoryreceptors,like:

mechanoreceptors,thermoreceptors,nocireceptors,

electromagnetic,chemoreceptors.

Thelabeledlineprinciple:eachofthetypesofsensationsworksonaspecifymodality,inotherwordseacharrangement

ofnervefiberworksonlyforonemodalityofsensation

(specificity).

Acommonfeature:allreceptorsafteracquiringinformationfromenvironmentgetanelectricalresponse(receptorpotential)

Thesemechanismsareforexample:mechanicaldeformationofthereceptorsarea,chemicalsignaling,changesoftemperature

alteringthepermeabilityofthemembrane,electromagnetic

radiation.

Maximumreceptorspotentialamplitude:about100mVatextremelyhighintensity.

Themorethereceptorpotentialriseabovethethresholdlevel,themorebecomestheactionpotentialfrequency.

Paciniancorpuscleasanexample:mechanicalexample,theactionpotentialisgivenbycompressionoftheunmyelinated

area,thenspreadtheneuronwhenitreachthefirstranviers

node.

Thereceptorshavethefeatureofadaptingthyselfafteraperiodoftime,slowingprogressivelytherateofpotentials.

Usuallymechanoreceptors.

Wecanfindalso:1. Tonicreceptors,slowlyadaptingduetocontinuousstimulusstrength,e.g.Golgitendonapparatus,painreceptors,

baroceptors.

2. Phasicreceptors,rapidlyadapting,itmeanstheyneedtoreadarapidchange,notacontinuousevent.E.g.Paciniancorpuscle.

3. Spatialsummation:usingmorefibersinvolvedinacontiguousareaofsensation,theyenhancethestimulusstrength.

4. Temporalsummation:increasingstrengthcanbereadbyincreasingthefrequencyofnervefibers.

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InstabilityandstabilityofNeuronalCircuits:

Easy!Itjuststatesthatwithoutanappropriatecontrolofthe

phenomenaofreverberationthebrainwouldenterinacircle

ofuncontrolledstimuliallaroundthesystemlikehowoccursinepilepticseizures.Inhibitorycircuitsthatstabilizethis

processavoidit:

Inhibitoryfeedback:itjustclosethecircuitatthestartingpoint,atthesamepathwayofthereceptor

Fatigue:itjustmeansthatsignalsbecomeprogressivelyweakeriftheexcitationistoolongandtoostrong.

Chapter47,keywordsandconcepts,ifneededIllmakeafocused

reviewAlargepre-viewofsomaticsenses:

Proprioceptors:I. Largediameter,myelinatedII. A,A Crudetouch,pain,temperature:I. Small,unmyelinatedII. Group4orTypeCfibers Finetouch,vibration,pressure:I. Large,myelinatedII. Group2,ortherestofTypeA AfewThermoreceptors: A,C Somaticmotorneurons(ventralhorn): A

Alittlehelpfultable

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Alittleanatomyreview:STRUCTURE

Unencapsulateddendriticendings:freeornakednerveendings;

abundantinepithelialtissueandconnectivetissueunderlying

epithelia.

Encapsulated:Nervefibersenclosedincapsuleofconnectivetissue,widelyshaped,sized,andfoundthroughoutthebody.

Therearealwaysinterrelationsinbetweenthedetectionand

transmissionoftactilesensations,amongtouch,pressureand

vibration.

Cutaneousreceptors:

Tactilesensation(i.e.touch,pressure,vibration,itch,tickle) Thermalsensations(cold&warmth) Cutaneousreceptorsdenselypopulatetipoftongue&lips,but

fewarefoundonbackofneck

Dendritesofcutaneousreceptorsmayormaynotbeenclosedincapsuleofepithelialorconnectivetissue

Nerveimpulsesofcutaneousreceptorsaretransmittedalongsomaticafferentneuroninspinalcordorcranialnervesthru

thalamustosomatosensoryareofparietallobeofcerebral

cortex

Fortouchandpressure:

1.Freenerveendings:commoninepithelialtissue

2.MeissnersCorpuscles:encapsulatednervefibers

-Numerousinhairslessportionsofskinthatareverysensitiveto

lighttouch,(lips,palms,soles)(+lowfrequencyvibration)

3.PacinianCorpuscles-encapsulatednervefibers;stimulatedby

heavypressure(Vibrationdetection)

-Locateddeeperinsubcutaneoustissues,tendons,ligaments

TherestofthischapterisboringlikehellsoIwillnotgetdeepon

this..ReviewitonthetableIpostedonthegroupifyouwannago

further

HopeIllmakeanotherdocumentfortheotherchapters!!!

Yourbelovedcolleague,AlessandroMotta.