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Objectives
• Goal /Aim:
• By the end of this session students should be able to understand the mechanism of
production & propagation of electrical changes occurring in excitable tissues.
• Student should be able to:
• To know the types of Disturbances across the Cell Membrane include action
potential & local response
• Define Action Potential
• Describe the Typical Action Potential in Large Myelinated Nerve fiber
• Explain & draw the Stages of Action Potential
• Describe the Types of Channels involved in Various Excitable Tissues
• Tell the difference between Voltage Gated Na+ and K+ Channels
• Describe the Propagation (Transmission) of Action Potential
• Explain Saltatory Conduction
• Differentiate between different Types of Action Potential
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Lesson contents
• Types of Disturbances across the Cell Membrane
• Definition of Action Potential
• Typical Action Potential in Large Myelinated Nerve fiber
• Stages of Action Potential
• Types of Channels involved in Various Excitable Tissues
• Voltage Gated Na+ and K+ Channels
• Na+
and K+
Conductance
• Propagation (Transmission) of Action Potential
• Saltatory Conduction
• Direction of Propagation
• Types of Action Potential
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Types of Disturbances across the Cell
Membrane
• TWO Types:
• Non-Propagated Potentials:
– Synaptic
– Generator
• Propagated
• Action Potential
Action Potential
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Action Potential
• Definition:
– Rapid changes in the membrane potential that spread
rapidly along cell membrane of excitable tissues
– Abrupt / sudden Change (reversal) in resting membrane
potential in response to a threshold stimulus.
– Sequence of events along the membrane of an Excitable
tissue in response to threshold stimuli
• Transmission of signals
• Sudden change, sudden end
• Transmission continues until fiber ends
• Transport of ions
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Activation and Inactivation of Na+
and
K+
Channels
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Summary of mechanism of development of
different stages of Action Potential
1. Resting stage (RMP)
(Polarized state)
-90 mV
1. Depolarization
Stimulus → sudden ↑in
Na+ Permeability
Na+ Leak Channels
From -90 (or-70) mv to
-50 mv
Voltage gated channels
(fast)
from -70 mv onwards
3. Overshoot Potential
4. Repolarization
Closure of Na+ Channels
Inactivation of Na+
Channels (Same
stimulus but Delayed)
Opening of K+ Channels
(Activation by same
stimulus but Delayed)
4. Hyperpolarization:
K+ Channels remain open
Na+ Out
4. Recovery Stage
Na+ K+ ATPase Pump
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Propagation
(Transmission)
of Action
Potential
• Electrotonic
Conduction.
• Local circuit of
Current along both
sides of membrane
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Propagation of Action Potential-II
(Saltatory Conduction)
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Self-Study Topics
• All-or-nothing Principle
– “Safety factor” for propagation
• Rhythmicity
I don’t t each my st udent s, I j ust
provide guidance and environment
conduct ive t o learning.
Albert Einstein (1877-1955)
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Summary
• Types of Disturbances across the Cell Membrane include action potential &
local response
• Action Potential is defined as Rapid changes in the membrane potential that
spread rapidly along cell membrane of excitable tissues
• Main stages of Action Potential include Resting stage (Polarized state),
Depolarization, Overshoot, Repolarization & Recovery Stage
• Types of Channels involved in Various Excitable Tissues include Voltage Gated
Na+ and K+ Channels, Na+
-K+
leak channels, & in some cases Ca++
channels
• Propagation (Transmission) of Action Potential occurs in All directions till the
end of the fiber
• Saltatory Conduction is the Jumping of Action Potential from one Node of
Ranvier to next in Myelinated fibers
• The advantages of Saltatory Conduction include increase velocity of conduction
& Energy Conservation
• Main Types of Action Potential include Spike Potential, Action Potential with
Plateau, Compound Action Potential & Biphasic Action Potential
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