Topic 2 sources of bioelectric potentials

COMPILED BY: Prof G B Rathod
EC department-BVM College,
Email: ghansyam.rathod@bvmengineering.ac.in
SOURCES OF BIOELECTRIC POTENTIALS

Outline
 Introduction
 Resting and action potentials
 Propagation of action potentials
 The bioelectric potentials
 Outcomes
 Reference
 Questions
BVM, EC, Prof.G.B.Rathod

Introduction
 Bioelectric Potentials: for various functions, body generate their own
monitoring signals which contain some useful information.
 These signals are bioelectric potentials associated with nerve
conduction, brain activity, heartbeat, muscle activity and so on.
 Its an ionic voltages and its produced by certain electrochemical activity
by special types of cells. Transducers can convert this ionic to electrical
voltages.
 First time Italian Professor, Luigi Galvani(1786), claim that he found
electricity in muscle of a frog’s leg. In human 1903 by Dutch physician
willem Einthoven.
 Development of semiconductor electronics, the research made easy.

Resting and Action Potentials
 Certain types of cells such as nerve and muscle cells are encased in
semipermeable membrane.
 Surrounding the cell contain body fluids which is conductive
solution having charged atoms kwon as atoms.
 The principal Ions are sodium(Na+), Potassium(K+), and
Chloride(CL-).
 Cell Membrane allows K+ and Cl- to enter inside but blocks the
Na+
 Because of that more Na+ outside and Cl- and K+ inside. Due to
less K+ , outside cell shows + and inside is -.

Polarized cell with its resting potential
Click here to see the process

 Equilibrium is reached with a potential difference across the membrane,
negative on the inside and positive on the outside.
 This membrane potential is called the “Resting Potential” of the cell and
maintained until some kind of disturbance upset the equilibrium.
 Research provided the value ranging from -60 mV to -100 mV. A Cell in
the resting state is said to be polarized.
 When a section of a cell membrane is excited by the flow of ionic
current or by some form of externally applied energy,, the membrane
allows some Na+ and try to reach some balance of potential inside and
outside. Same time the some K+ goes outside but not rapidly like
sodium.

Fig: Depolarization of a cell.
•As a result, the cell has slightly
Positive potential on the inside
Due to the imbalance of the
Potassium ions.
•This potential is known as “action Potential”
and is approximately +20 mV.
•A cell that has been excited and that displays
an action potential is said to be depolarized and
process from resting to action potential is
called depolarization

Fig: Depolarization cell during an action potential

With in short time once again cell try to
Be in resting state.
Waveform of the action potential

 The time scale depends on the cell producing the potential.
 In nerve and muscle cells, repolarization occur as spike around 1 msec total
duration. Heart muscle need 150 to 300 msec.
 Regardless of the method by which cell is excited or the intensity of the
stimulus, the action potential is always the same for any given cell. This is
known as the all-or-nothing law.
 The small period of time where the cell can not respond to any new stimulus is
known as a absolute refractory period, last for 1 msec in nerve cells.
 Following the absolute refractory period, there occurs a relative
refractory period, during which another action potential can be triggered
but much stronger stimulation is required.

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

The Bioelectric Potentials
 The Electrocardiogram(ECG)
 The Electroencephalogram(EEG)
 The Electromyogram(EMG)
 The Electroretinogram(ERG)
 The Electro-oculogram(EOG)
 The Electrogastrogram(EGG)

 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.

 Right atrium  tricuspid valve  right ventricle
 Right ventricle  pulmonary semilunar valve  pulmonary
arteries  lungs
 Lungs  pulmonary veins  left atrium
 Left atrium  bicuspid valve  left ventricle
 Left ventricle  aortic semilunar valve  aorta
 Aorta  systemic circulation

 Electrical activity is recorded by electrocardiogram (ECG)
 P wave corresponds to depolarization of SA node
 QRS complex corresponds to ventricular depolarization
 T wave corresponds to ventricular repolarization
 Atrial repolarization record is masked by the larger QRS
complex

 The Electroencephalogram(EEG)
 The recorded representation of bioelectric potential by the
neuronal activity of the brain is called the
electroencephalogram.
 The waveform varies greatly with the location of the
measuring electrodes on the surface of the scalp.

Frequency Range SignalType Activity
Below 3.5 Hz Delta Deep sleep
From 3.5 Hz to about 8 Hz Theta Fall aslpeep
From about 8 Hz to about 13 Hz Alpha Drowsy person
Above 13 Hz Beta Paradoxial sleep, Rapid eye
movement(REM)

Click here to
See how the EEG
Test performs..

 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.

Click here to see how EMG is performed…

 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.
 Electroretinography measures the electrical responses of various cell types
in the retina, including the photoreceptors (rods and cones), inner retinal cells
(bipolar and amacrine cells), and the ganglion cells. Electrodes are placed on the
surface of the cornea (DTL silver/nylon fiber string or ERG Jet) or on the skin
beneath the eye (Sensor Strips) to measure retinal responses.
 Clinically used mainly by ophthalmologists and optometrists,
the electroretinogram (ERG) is used for the diagnosis of various retinal
diseases

 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.

Outcomes
 The basic of potential generation from the body
 Understanding of basic concept of various bioelectric signals
from the human body.

References
 Book:“Biomedical instrumentation and measurements “ ,by
L. Cromwell, F .Weibell, and E. Pfeiffer. PHI publication 2nd
Edition
 www.msu.edu/anatomy
 www.humbleisd.net/cms/.../Anatomy
 www.lavc.edu/instructor/...k/.../Lecture
 web.as.uky.edu/Biology/faculty

Questions?????
Thank you

Topic 2 sources of bioelectric potentials

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