Loai Alzghoul

Loai.physiology@yahoo.com

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.