Topic 2 sources of bioelectric potentials

Biomedical Instrumentation

1. COMPILED BY: Prof G B Rathod
EC department-BVM College,
Email: [email protected]
SOURCES OF BIOELECTRIC POTENTIALS

2. Outline
Introduction
Resting and action potentials
Propagation of action potentials
The bioelectric potentials
Outcomes
Reference
Questions
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3. Introduction
BioelectricPotentials:forvariousfunctions,bodygeneratetheirown
monitoringsignalswhichcontainsomeusefulinformation.
Thesesignalsarebioelectricpotentialsassociatedwithnerve
conduction,brainactivity,heartbeat,muscleactivityandsoon.
Itsanionicvoltagesanditsproducedbycertainelectrochemicalactivity
byspecialtypesofcells.Transducerscanconvertthisionictoelectrical
voltages.
FirsttimeItalianProfessor,LuigiGalvani(1786),claimthathefound
electricityinmuscleofafrog’sleg.Inhuman1903byDutchphysician
willemEinthoven.
Developmentofsemiconductorelectronics,theresearchmadeeasy.
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4. Resting and Action Potentials
Certaintypesofcellssuchasnerveandmusclecellsareencasedin
semipermeablemembrane.
Surroundingthecellcontainbodyfluidswhichisconductive
solutionhavingchargedatomskwonasatoms.
TheprincipalIonsaresodium(Na+),Potassium(K+),and
Chloride(CL-).
CellMembraneallowsK+andCl-toenterinsidebutblocksthe
Na+
BecauseofthatmoreNa+outsideandCl-andK+inside.Dueto
lessK+,outsidecellshows+andinsideis-.
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5. Resting and Action Potentials
Polarized cell with its resting potential
Click here to see the process
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6. Resting and Action Potentials
Equilibriumisreachedwithapotentialdifferenceacrossthemembrane,
negativeontheinsideandpositiveontheoutside.
Thismembranepotentialiscalledthe“RestingPotential”ofthecelland
maintaineduntilsomekindofdisturbanceupsettheequilibrium.
Researchprovidedthevaluerangingfrom-60mVto-100mV.ACellin
therestingstateissaidtobepolarized.
Whenasectionofacellmembraneisexcitedbytheflowofionic
currentorbysomeformofexternallyappliedenergy,,themembrane
allowssomeNa+andtrytoreachsomebalanceofpotentialinsideand
outside.SametimethesomeK+goesoutsidebutnotrapidlylike
sodium.
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7. Resting and Action Potentials
Fig: Depolarization of a cell.
•Asaresult,thecellhasslightly
Positivepotentialontheinside
Duetotheimbalanceofthe
Potassiumions.
•Thispotentialisknownas“actionPotential”
andisapproximately+20mV.
•Acellthathasbeenexcitedandthatdisplays
anactionpotentialissaidtobedepolarizedand
processfromrestingtoactionpotentialis
calleddepolarization
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8. Resting and Action Potentials
Fig: Depolarization cell during an action potential
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9. Resting and Action Potentials
With in short time once again cell try to
Be in resting state.
Waveform of the action potential
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10. Resting and Action Potentials
Thetimescaledependsonthecellproducingthepotential.
Innerveandmusclecells,repolarizationoccurasspikearound1msectotal
duration.Heartmuscleneed150to300msec.
Regardlessofthemethodbywhichcellisexcitedortheintensityofthe
stimulus,theactionpotentialisalwaysthesameforanygivencell.Thisis
knownastheall-or-nothinglaw.
Thesmallperiodoftimewherethecellcannotrespondtoanynewstimulusis
knownasaabsoluterefractoryperiod,lastfor1msecinnervecells.
Followingtheabsoluterefractoryperiod,thereoccursarelative
refractoryperiod,duringwhichanotheractionpotentialcanbetriggered
butmuchstrongerstimulationisrequired.
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11. Propagation of action potentials
The rate at which an action potential moves down a fiber or
is propagate from cell to cell is called the propagation rate.
In nerve fiber the propagation rate is also called the nerve
conduction rate, or conduction velocity. Velocity range in
nerves is from 20 to 140 meters per second.
In heart muscle, the rate is slower, average 0.2 to 0.4 m/sec
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12. The Bioelectric Potentials
The Electrocardiogram(ECG)
The Electroencephalogram(EEG)
The Electromyogram(EMG)
The Electroretinogram(ERG)
The Electro-oculogram(EOG)
The Electrogastrogram(EGG)
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13. The Bioelectric Potentials
The Electrocardiogram(ECG)
The bio-potentials generated by the muscles of the heart
result in the electrocardiogram(ECG). German word EKG
To understand the ECG generation, Need to understand the
anatomy of the heart.
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14. The Bioelectric Potentials
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15. The Bioelectric Potentials
Right atrium tricuspid valveright ventricle
Right ventricle pulmonary semilunarvalvepulmonary
arteries lungs
Lungs pulmonary veins left atrium
Left atrium bicuspid valveleft ventricle
Left ventricle aortic semilunarvalveaorta
Aorta systemic circulation
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16. The Bioelectric Potentials
Electrical activity is recorded by electrocardiogram (ECG)
P wave corresponds to depolarization of SA node
QRS complexcorresponds to ventricular depolarization
T wave corresponds to ventricular repolarization
Atrialrepolarizationrecord is masked by the larger QRS
complex
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17. The Bioelectric Potentials
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18. The Bioelectric Potentials
TheElectroencephalogram(EEG)
Therecordedrepresentationofbioelectricpotentialbythe
neuronalactivityofthebrainiscalledthe
electroencephalogram.
Thewaveformvariesgreatlywiththelocationofthe
measuringelectrodesonthesurfaceofthescalp.
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19. The Bioelectric Potentials
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20. The Bioelectric Potentials
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21. The Bioelectric Potentials
FrequencyRange Signal Type Activity
Below 3.5 Hz Delta Deep sleep
From 3.5 Hz to about 8 Hz Theta Fallaslpeep
Fromabout 8 Hz to about 13 HzAlpha Drowsy person
Above 13 Hz Beta Paradoxialsleep, Rapid eye
movement(REM)
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22. The Bioelectric Potentials
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23. The Bioelectric Potentials
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Click here to
See how the EEG
Test performs..

24. The Bioelectric Potentials
EMG: The bioelectric potentials associated with muscle
activity constitute the electromyogram.
Can be measure on the surface of the body or by penetrating
the skin using needle electrodes.
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25. BVM, EC, Prof.G.B.Rathod
Click here to see how EMG is performed…

26. The Bioelectric Potentials
ERG: Eelctoretinogram: A record of the complex pattern of the bioelectric
potentials obtain from the retina of the eye. This is usually a response to a visual
stimulas.
Electroretinographymeasurestheelectricalresponsesofvariouscelltypes
intheretina,includingthephotoreceptors(rodsandcones),innerretinalcells
(bipolarandamacrinecells),andtheganglioncells.Electrodesareplacedonthe
surfaceofthecornea(DTLsilver/nylonfiberstringorERGJet)orontheskin
beneaththeeye(SensorStrips)tomeasureretinalresponses.
Clinicallyusedmainlybyophthalmologistsandoptometrists,
theelectroretinogram(ERG)isusedforthediagnosisofvariousretinal
diseases
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27. The Bioelectric Potentials
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EOG: Electro-oculogram: A measure of the variation in the
corneal-retinal potential as affected by the position and
movement of eye.
EGG:Electrogastrogram: The EMG patterns associated with
the peristaltic movement of the gastrointestinal tract.

28. Outcomes
The basic of potential generation from the body
Understanding of basic concept of various bioelectric signals
from the human body.
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29. References
Book: “Biomedical instrumentation and measurements “ ,by
L. Cromwell, F .Weibell, and E. Pfeiffer. PHI publication 2
nd
Edition
www.msu.edu/anatomy
www.humbleisd.net/cms/.../Anatomy
www.lavc.edu/instructor/...k/.../Lecture
web.as.uky.edu/Biology/faculty
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30. Questions?????
Thank you
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