ACTION POTENTIAL

1. MEDICAL
ELECTRONICS
EC8073
Faculty Handled By:
Mrs.P.Sivalakshmi AP/ECE
Section: A & B
FIFTH SEMESTER-III YEAR- (2019-2023 BATCH)
SESSION:3
DATE: 27.08.2021

2. UNIT I- ELECTRO-PHYSIOLOGY AND BIO-POTENTIAL RECORDING
• Sources of bio medical signals
• Bio-potentials
• Bio potential electrodes
• Biological amplifiers
• ECG-Electrocardiogram (ECG or EKG)
• EEG- Electroencephalogram (EEG)
• EMG-Electromyography
• PCG-Phonocardiogram
• Typical waveforms and signal characteristics

3. DiscussionTopics
RECAP:
• Electro Physiology
• Bio-Potentials
 Resting Potential
 Action Potential
• Propagation of Action potential
• Propagation rate Or Conduction Velocity
• All or None law
• Absolute refractory period
• Relative refractory period
• Goldman–Hodgkin–Katz (GHK) Equation

4. Resting Potential

5. Resting Potential

6. Resting Potential
Polarized cell with its resting potential.

8. DEPOLARIZATION
Depolarization of a cell. Na + ions rush into the cell while
K + ions attempt to leave

9. REPOLARIZATION

14. PROPAGATION OF ACTION POTENTIALS

15. • When a cell is excited and generates an action potential ionic
currents begin to flow.
• The rate at which an action potential moves down a fiber or is
propagated from cell to cell is called the propagation rate.
• In nerve fibers the propagation rate is also called the nerve
conduction rate, or conduction velocity.
• This velocity varies widely, depending on the type and diameter of the nerve fiber. The usual velocity range in
nerves is from 20 to 140 meters per second (m/sec).
• Propagation through heart muscle is slower, with an average rate from 0.2 to 0.4 m/sec. Special time-delay
fibers between the atria and ventricles of the heart cause action potentials to propagate at an even slower rate,
0.03 to 0.05 m/sec.
Conduction Velocity

16. H. P. Bowditch
In 1905 the Cambridge
physiologist Keith Lucas
extended the "all-or-
none" principle
(introduced by H. P.
Bowditch for the cardiac
tissue) to skeletal muscle
and nerve fibres.
https://www.youtube.com/watch?v=4M1zzT9J_y4

17. Regardless of the method by which a cell is excited
or the intensity of the stimulus (provided it is
sufficient to activate the cell), the action potential
is always the same for any given cell. This is known
as the all-or-nothing law.

19. The net height of the action
potential is defined as the
difference between the potential
of the depolarized membrane at
the peak of the action potential
and the resting potential.
Following the generation of an
action potential, there is a brief
period of time during which the
cell cannot respond to any new
stimulus. This period, called
the absolute refractory period,
lasts about 1 m sec in nerve cells.
Following the absolute
refractory period, there occurs a
relative refractory period, during
which another action potential
can be triggered, but a much
stronger stimulation is required.
In nerve cells, the relative
refractory period lasts several
milliseconds. These refractory
periods are believed to be the
result of after-potentials that
follow an action potential.

21. GOLDMAN–HODGKIN–KATZ (GHK) EQUATION:
The Goldman–Hodgkin–Katz (GHK) voltage equation, more commonly
known as the Goldman equation, is an equation used to calculate the
electrical equilibrium potential across the cell's membrane in the presence
of more than one ions taking into account the selectivity of membrane's
permeability. The magnitude of membrane potential is determined by

22. GOLDMAN–HODGKIN–KATZ (GHK) EQUATION:
where
E is the potential difference of an ion between membranes
R is the universal gas constant; R = 8.314471 J mol-1
T is the thermodynamics temperature, in Kelvin; 0 K = -273.15oC
z is the number of moles of electrons transferred between membranes (defined by the Valency of ion)
F is the Faraday's constant; F = 96,485.3415 C mol-1
PX is the permeability of the membrane to a particular ion (X)
[X]o is the concentration of ion outside the membrane
[X]i is the concentration of ion inside the membrane
According to Goldman’s equation Resting Potential is -86.8 mV

24. SIMULATION OF ACTION POTENTIAL
https://phet.colorado.edu/sims/html/neuron/latest/neu
ron_en.html