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Action Potential = ALL x NOTHING
3
The Action PotentialThe Action Potential
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
Electrotonic potential
K Na K K Na
Passive increase in positive charge
- 75 mV
4
The Action PotentialThe Action Potential
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
Electrotonic potential
Opening of voltage-gated sodium channel
K K K
- 55 mV
Na Na
threshold
5
The Action PotentialThe Action Potential
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
Electrotonic potential
Depolarisation due to sodium influx
Opening of voltage-gated sodium channel
K K K
- 40 mV
Na Na
6
The Action PotentialThe Action Potential
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
Electrotonic potential
Depolarisation due to sodium influx
Inactivation of voltage-gated sodium channel
K K K
+ 50 mV
Na Na
voltage-gated sodium channels turn to the inactivation phase
7
The Action PotentialThe Action Potential
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
Electrotonic potential
Depolarisation due to sodium influx
opening of voltage-gated potassium channel
K K
+ 50 mV
Na NaK
8
The Action PotentialThe Action Potential
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
Electrotonic potential
Depolarisation due to sodium influx
opening of voltage-gated potassium channel
K K
- 85 mV
Na NaK
Repolarization due
to potassium influx
9
The Action PotentialThe Action Potential
Resting potential (-75 mV)
Equilibrium potential of sodium (+60 mV)
Electrotonic potential
Depolarisation due to sodium influx
K K
- 75 mV
Na NaK
closing of voltage-gated potassium channel
repolarization dueto potassium influx
Repolarisation dueto potassium influx
Membrane potential approaches the ENa and voltage-gated sodium channels turn to the
inactivation phase
Hyperpolarisingafterpotential
Hyperpolarisingafterpotential
Dentistry 07 10
The Action PotentialThe Action Potential
Electrotonic potential
Opening of voltage-controlled sodium
channel
Inactivation of voltage-controlled sodium channel
Opening of voltage-controlled potassium
channel
Resting potential (-75 mV)
Equilibrium potential of sodium (+60 mV)
threshold
Hyperpolarization due to more outflux of potassium ions
Hyperpolarization due to more outflux of potassium ions
11
Properties of action potentials• Action potentials:
• are all-or-none events
threshold
-70
+60
mV
Stim
ulus
0
• APs do not summate - information is coded by frequency not amplitude.
Dentistry 07 12
Recording membrane potential Recording membrane potential
+ 60 -
+ 30 -
0 -
- 30 -
- 60 -
- 90 -
mV
Electrotonic potentialLocalized non propagated
Action potential
Graded Potentials
Excitable cell: NEURON and MUSCLE CELL
Neuron
F8-2
• Axons carry information from the cell body to the axon terminals.
• Axon terminals communicate with their target cells at synapses.
Communication Between Neurons
• Electrical synapse Chemical synapse
Dentistry 07 19
• It is recorded by cathode ray oscilloscope
it is negative in polarized (resting, the membrane can be excited) state with the potential difference inside the cell membrane is negative relative to the outside.
Recording of Resting and action potentials
+
+
+
++ +
+
+
+
+ +
–
––– –
––
–––
–
Voltmeter
– +0 mV-70 mV +
Terminology Associated with Changes in Membrane Potential
F8-7, F8-8
• Depolarization- a decrease in the potential difference between the inside and outside of the cell.
• Hyperpolarization- an increase in the potential difference between the inside and outside of the cell.
• Repolarization- returning to the RMP from either direction.
• Overshoot- when the inside of the cell becomes +ve due to the reversal of the membrane potential polarity.
