09-22_Spontaneous subthreshold activity at motor nerve endings

09-22_Spontaneous subthreshold activity at motor nerve endings

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 109 J.Physiol. (I952), II7, I09-I28 SPONTANEOUS SUBTHRESHOLD ACTIVITY AT MOTOR NERVE ENDINGS BY P. FATT AND B. KATZ From the Biophysics and PhysiologyDepartments, UniversityCollege, London (Received5December1951) Thepresentstudyarosefromthechanceobservationthat end-plates of resting musclefibresaretheseatofspontaneouselectric discharges whichhavethe characterofminiature end-platepotentials. The occurrence ofspontaneous subthreshold activity at an apparently normal synapse isofsome general interest,and afull descriptionwillbe givenhereof observationswhichhave beenbrieflyreportedelsewhere (Fatt & Katz,1950a). METHOD Theintracellularrecordingtechnique (Ling & Gerard,1949;Nastuk & Hodgkin,1950)was used inmostexperiments,confirmatoryevidencebeingobtainedwithexternalrecordinginafewcases. The adaptation ofthe microelectrode technique to a studyofthe motor end-platehas been describedindetailina previouspaper(Fatt& Katz,1951). Thepreparationwas them. ext. longusdig. IV andm. sartoriusofthefrog. Inafew experi- ments, limb and abdominal muscles oflizards (Lacerta dugesii) and tortoises(Testudo graeca) were used. RESULTS Preliminaryobservations Inthecourseofsomeearlier work, while recording fromthesurfaceofisolated musclefibres,we occasionally noticedaspontaneous discharge ofsmallmono- phasicactionpotentials. The potentials variedsomewhatinsize,buthad a very consistenttimecourse, risingrapidlyin 1-2 msec, and decliningmore slowly,toone-halfinabout 3-4msec. Theywere localizedat one regionofthe fibre,andintheir shape and spatialspread resembledtheend-platepotential (e.p.p.)(cf.Eccles,Katz & Kuffler, 1941;Fatt& Katz, 1951). Moreover,the dischargedisappearedwhen a moderate doseofcurarine was appliedtothe muscle. Not much attentionwas paidtothephenomenon atthetime,and itwas suspectedtobeduetoalocalinjurydischargeatthenerveendings,theaxon havingbeencutclosetothemusclefibre. Inmore recentexperiments,how- P. FATT AND B. KATZ ever,we observedthesame phenomenon innerve-musclepreparationswhich seemedtobeabove any suchsuspicion,andthisinducedustoexaminethe natureofthe dischargeindetail. Localizationofthespontaneousdischargeattheend-plateregion Theformalresemblanceofthespontaneousdischargestothee.p.p.suggests thattheyoriginateatthenerve-musclejunction.Thisisnotbyitselfcritical evidence,foranybriefdisturbanceofthemusclemembrane-anywherealong thefibre-wouldbefollowed byalocalpotentialchangesimilarintimecourse andspatialspreadtothee.p.p.(seeEcclesetal.1941;Katz,1948;Fatt& Katz, 1951). A more decisive point was thatthe discharge couldnever beseenat Fig. 1. Localizationof spontaneousactivity. M. ext. 1. dig.IV. Intracellularrecording. PartA was recorded at the end-plate,part B at a distance2m m away, inthesame muscle fibre....
View Full Document

This note was uploaded on 09/21/2010 for the course NACS 641 taught by Professor Areneda during the Fall '10 term at University of Maryland Baltimore.

Page1 / 20

09-22_Spontaneous subthreshold activity at motor nerve endings

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online