BIOPACLABEXPERIMENT Principlesof Electromyography1: Fundamentals of Motor Unit Recruitment PHYSIOLOGICAL CONCEPTS Thehumanbodyhasthreekindsofmuscletissue-skeletalmuscle,cardiacmuscle,andsmoothmuscle. Eachkind of muscle tissue differs fromthe other two in theirlocation, their microscopic structure, their control bynervousandendocrinesystems,andhowtheyper-formspecifictasksto maintain homeostasis. SmoothMuscle Tissue Smooth muscle is located in the walls of hollow internal organssuchasbloodvessels,thestomach,intestines, and theairwaysof thelungs.Smooth muscle cells have a singlenucleusand are generally spindle shaped rather than cylindrically shaped(Figure2.1). Their cytoplasm has a non-striated, or smooth, appearance, and they are frequentlyconnectedtoformcordsor sheets.Smooth musclecellsaresuppliedwithnervefibersof theauto-nomicnervoussystem.Thus,smoothmuscleactionis involuntary.Smoothmusclecontractionsareslowand powerful.Contractionofsmoothmusclechangesthe internaldiameterorvolumeof holloworgansandis thereby used to regulate the passage of material through thestomachandintestines,thepressureandflowof bloodthroughbloodvessels,andtheflowofair through the airways of lungs. Cardiac Muscle Tissue Cardiac muscle forms the middle layer of the heart wall calledthe myocardium.Cardiac musclecellsareshort, cylindricalcells,eachhavingasinglenucleusanda cytoplasm markedby alternatinglightand dark bands called striations. Striated cardiac muscle cells are together in series at junctions characterized by low elec-'.tlical resistance bridges that allow electricarimpulses to

rapidlyspreadfromcelltoc_ell.Thus,_ cardiacmuscle cells function together as a umt when stimulated to con-tract.Cardiacmuscletissueincludesasys-temthatinitiatestheheartbeatandcoordmates contractionofcardiacmuscleinpartsoftheheart. Control of the heartbeat isby way of several hormones thatalterfrequencyandstrengthofthecontractions and by way of the autonomic nervous system that inner-vatesthe heart with involuntary motor fibers. Skeletal Muscle Tissue Skeletal muscle, as its name suggests, isusually attached totheskeleton,althoughsomeskeletalmusclesare attachedtootherkindsofconnectivetissue. Contraction and shortening of. skeletal muscle produces movement,suchaswhenextending theleginwalking or flexingtheforearmwhenliftinganobject.Skeletal muscle tissue makes up most of the human body's mass and can alsoproduce significant heat, when needed,by way of special contractions that characterize shivering. Regardlessof kind, the primary functionof muscle tissueistoconvertchemicalenergyintomechanical work,and in doing so, the muscle contracts and physi-cally shortens.In this chapter, we willinvestigate some aspectsof neuromuscular control involving the somatic motorsystemanditscontrolofskeletalmuscles.In otherchapters,wewillstudy .physiologicphenomena associated with other kindsof muscle,suchaselectro-physiology of the heart. Humanskeletal muscleconsistsofhundredsof individualcylindricallyshapedcells,calledmuscle fibers,bound together by connective tissue. In the body, _ skeletalmusclesare 'stimulated ' to contractby' somatic motor nerves:which carry signalsin the formof nerve . impulsesfromthebrainor spinalcordtotheskeletal Principles of1: Fundamentals of Motor ... (.. . - . . Cerebrum Right Hemisphere FIGURE2.3 Primary Somatic Motor CortE;lx Precentral Gyrus From Basic Human Physiology by RichardPflanzer. Copyright e 2001by Richard pflanzer. Reprinted by permission of Kendaii!Hunt Publishing Company. REQUIREDEQUIPM.ENT ANDSUPPLIES Computersystem:Macintosh-minimum68020, System 7, 4MB RAM;or PCrunning Windows95,4 MB RAM BIOPAC Student Lab Software 3.70 BIOPAC MP 30 data acquisition unit with AClOOA transformer BIOPAC SS2L electrode lead cables BIOPACGELl electrode geland ELPAD BIOPAC EL503disposable vinyl electrodes BIOPACOUTlheadphones Although theysound complex,electrodes are very sim-pledevicesthatconsistofasmallpieceofmetal designedtomakeindirectcontact withtheskinand a largeradhesiveplasticdisk.Eachelectrodeisabout1 inchindiameterandisstickyononesidesoitwill adhere to skin. If you look closely at the electrode, you can seethat there isa smallpieceof plasticmesh filled with a gel.Gelconducts electricity better than skin and is more flexible than the metal part of the electrode; this allows the subject's skin to flex and change shape some-what without losingthe electricalconnectionwiththe metalpartoftheelectrode.Theseelectrodescomein stripsoften,andyoushouldnot removean electrode from the backing until you are ready to use it. The pur-pose of an electrode isto act as a"connector"between / EXPERIMENTAL METHODSthe SS2L cable and the subject's skin; where electric sig-nalsareeasiesttodetect. . Electrodeshavenomoving SurfaceRecordingElectrodesparts, so there isnothing you have-to do to get an elec- , The disposable electrodesusedby the BIOPAC Studenttrodeto"work,"althoughthekeytoworkirigwith Labare standarddisposableelectrodesandarewidelyelectrodesis_makingsurethat everythingis _co'nnected usedmclinical,research,andteaching . ilpplications. __ - properly. ..'\ 20:_BI()PAC.Lab' . ' 1: ... ,.--. -.= I .-.: If anelectrodeisabletomakeagoodconnection withthesubject'sskin,thesignalsthatappearonthe B0PACStudentLabwillberelativelyaccurate. However, if an electrode is not adhering well to the skin, thenthesignalplottedonthescreencanappear "fuzzy."Some referto thisas"noise,"andalthoughit isalwayspresenttosomedegree,itisdesirableto reduce it asmuch aspossible. There are several things you can do to reduce noise whenelectrodesareconnected.Acommon problemis thatsomethingonthesurfaceoftheskiniscoming between the electrode and the skin. For instance, if there is too much hair between the outer layer of skin and the electrode, then you may not be able to sense the 'electri-calactivitytakingplacebelowthesurfaceof theskin. Since in this experiment we do not recommend shaving thearmforthe sakeof gettingagoodsignal,thebest you can do isto try to place the electrodes where there isthe least amount of hair. One way you can improve electrode connections is to gently rub the area where the electrode is to be placed withanELPADelectrodepad(includedwiththe BIOPACStudentLab).TheELPADabradestheskin, removingathinlayer of dead skinfromthe skin's sur-face.Sincedeadskindoesnotconduct electricityvery well,thisimprovestheconnectionbetweentheelec-trode and the skin. It isalso agood idea to attachthe electrodes afew minutesbeforeyouaregoingtousethem.Thebest resultsareachievedbyputtingtheelectrodesinplace about 5minutesbefore youbeginrecordingdata. This givestheelectrodestimetoestablishcontactwiththe surface of the skin. '.; ,.. -FIGURE2.4. '-Courtesy of BIOPAC Systems,. .:. Attachingelectrodes:Toattachanelectrode,peel theelectrodefromitsbackingandplaceit onthearea indicated in the lesson. Youmay want to squeeze a drop ortwoof electrodegelontoeitherthesurfaceof the skinor ontothe electrodetohelp ensurethattheelec-trodewillmakegoodelectricalcontactwiththeskin. Onceitisinplace,pressdownfirmlyontheelectrode withtwofingersand rockthe electrodebackandforth for afewseconds. This will ensure that itis adhering to theskinasmuchaspossible.Withtheelectrodein place,attachtheelectrodeleadfromtheSS2Ltothe snap connectbron top of the electrode.Each color lead is so it is important that you attach each cable to the appropriate electrodesite. Removingelectrodes:Onceyouhavefinished recordingdata,disconnectthelead,peeltheelectrode off the skin,and dispose of the electrode. Set Up 1.Turnonyourcomputer.Thedesktopshould appear onthemonitor.If it doesnot appear,then ask the laboratory instructor for assistance. 2.TurnontheMP30dataacquisitionunit.The power switch ison the rear panel.AnLEDon the front panel indicates power on. If the LED does not light up when the power switch is turned on, check 'to make sure the AClOOA transformer (which sup-pliespower to theMP30)ispluggedintoanelec-trical outlet on the laboratory bench. 3.Select a subject for electromyography.Usingacot-tonballorpapertowelsoakedinalcohol,oran ELPAD,and cleansetheskinonthemedialaspect of the anterior forearm (Figure 2.4) where the EMG _..,,,' PrinCiplesof Electromyography 1:Fundamentals of Motor Unit Recruitment 21 J electrodeswillbeattached.Forthefirstrecording segment,selectthesubject'sdominantforearm (generallytherightforearmif thesubjectisright-handed or the left forearm if the subject isleft-hand-ed) and attach the electrodes as shown. This willbe Forearm1.Usethesubject'sotherforearmforthe secondrecording segment. This willbeForearm 2. 4.Plug the electrode assembly (SS2L)into Channel 3. Attachthecolor-codedelectrodeleadstothesub-jectaccordingtoFigure2.4.Thesubjectistobe seatedatthelaboratorybenchwiththeselected forearm resting on thetabletopand thepalm fac-ing upward. 5.Locatethe"BIOPAC Student Lab"folder,openit, andstarttheBIOPACStudentLabprogram.A prompt(Figure2.5)willappearaskingyouto choose alesson.ChooseLesson 1("LOl-EMG-1") by clicking on it to highlight it, then click OK. 6.A prompt (Figure 2.6) should appear asking you to "Please type in your filename."The program does thisso that it can store allthe data filesyou create inoneplace-making iteasierforyoutoretrieve data later. .- .-Please Choose alesson:~ L01-EMG-1 L02-EMG-2 L03-EEG-1 L04-EEG-2 .LOS-ECG-1 LOS-ECG-2 L07-ECG&P-1 LOB-Resp-1 L09-Poly-1 L10-EOG-1 L11-React-1 L14-Biofbk-1 L15-Aero-1 L16-Bp-1 L 17-Hs-1 Review Saved Daia FIGURE2.5 BiopacStudent Lab FIGURE2.6 OK I Q u ~ I " ~ You can enter your real name, a nickname, or the name of your groupif youare working withother students_However,theBIOPACStudentLabsoft-ware does not allow for duplicate names, so if there are alot of other students using your computer and youtry to log on as "John," for example, there isa goodchancetheBIOPACStudentLabsoftware willaskyoutouseadifferentname.Thebest approachisto select andtypeinauniqueidentifi-er,suchasthesubject'snicknameorstudentID number,yourfullname,orsomecombinationof yournameandotherlettersand/ornumbers(e-g., "JohnF"or"John3").It isagoodideato usethe samelog-onnameforeachlesson. Whichever log-onnameyouchoose,besuretowriteit down so thatyoucankeeptrackofwhereyourdatais stored. Once youenteryour nameand chooseOK,the BIOPACStudentLabsoftwarecreatesafolder insidethe"DataFiles"folder,whichisinsidethe "BIOPACStudentLab"folderonyour computer. Thisiswhereallyourdatawillbestored.If you choosethesamefilenameforotherlessons,they willalsobestoredinthisfolder..However,if you try to use the same file name when you repeat ales-sonorifsomeoneelsetriestochoosethesame name, the program will insist that you choose adif-ferentname.Thefilesinsideyourfoldercanbe moved,copied,duplicated,anddeletedjustlike anyother files. If you wish, you can copy them to adiskette as abackup or in case you want to view them later.Check with your instructor or lab assis-tant for more information on how to do this. 7.After youlog on,awindowsimilarto Figure2.7 willbedisplayed.Checktoensuretheproper placementofelectrodesandelectrodeleadsand makecertainthattheelectrodeassemblyis plugged into Channel 3. This concludes the set-up procedures. FIGURE 2.7 Anr 11GfJf