1. Resting Membrane Potential

4. Fig a,b

5. Nernest equation E (mV) = - 61.log (Ci/Co)
E = Equilibrium potential for a univalent ion
Ci = conc. inside the cell.
Co = conc. outside the cell.

6. Recording of Resting and action potentials
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. –
-70 mV + +
0 mV
Voltmeter + –
Dentistry 07

8. 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.

9. Types of Ion Channels

12. Membrane Potential: Goldman Equation
P = permeability
at rest: PK: PNa: PCl = 1.0 : 0.04 : 0.45
Net potential movement for all ions
known Vm:Can predict direction of movement of any ion ~

19. The action potential (AP)
An action potential is:
A regenerating depolarization of membrane potential that propagates along an excitable membrane.
[propagates = conducted without decrement (an ‘active’ membrane event)]
[excitable = capable of generating action potentials]
1 ms
+70
(mV)
-80
ENa EK
Action potentials:
are all-or-none events
need to reach threshold
have constant amplitude
do not summate
are initiated by depolarization
involve changes in permeability
rely on voltage-gated ion channels
downstroke

20. Recording membrane potential
+ 60 -
+ 30 -
0 -
- 30 -
- 60 -
- 90 - mV
Electrotonic potential
Localized non propagated
Action potential

21. Threshold and Action Potentials
Threshold – membrane is depolarized by 15 to 20 mV
Established by the total amount of current flowing through the membrane
Weak (subthreshold) stimuli are not relayed into action potentials
Strong (threshold) stimuli are relayed into action potentials
All-or-none phenomenon – action potentials either happen completely, or not at all

22. The Action Potential Equilibrium potential of sodium (+60 mV) - 75 mV
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV) K Na
- 75 mV
Passive increase in positive charge
Electrotonic potential

23. The Action Potential threshold
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
- 55 mV Na Na K K K
Opening of voltage-gated sodium channel
threshold
Electrotonic potential

24. The Action Potential Equilibrium potential of sodium (+60 mV) - 40 mV
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
Depolarisation due to sodium influx
- 40 mV Na Na K K K
Opening of voltage-gated sodium channel
Electrotonic potential

25. voltage-gated sodium channels turn to the inactivation phase
The Action Potential
voltage-gated sodium channels turn to the inactivation phase
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
Depolarisation due to sodium influx
+ 50 mV Na Na K K K
Inactivation of voltage-gated sodium channel
Electrotonic potential

26. The Action Potential Equilibrium potential of sodium (+60 mV) + 50 mV
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
Depolarisation due to sodium influx
opening of voltage-gated potassium channel K
+ 50 mV Na
Electrotonic potential

27. The Action Potential Equilibrium potential of sodium (+60 mV) - 85 mV
Resting potential (-75 mV)
Equilibrium potential of potassium (-95 mV)
Equilibrium potential of sodium (+60 mV)
Depolarisation due to sodium influx
Repolarization due
to potassium influx
opening of voltage-gated potassium channel K
- 85 mV Na
Electrotonic potential

28. Resting potential (-75 mV) Equilibrium potential of sodium (+60 mV)
The Action Potential
Membrane potential approaches the ENa and voltage-gated sodium channels turn to the inactivation phase
Resting potential (-75 mV)
Equilibrium potential of sodium (+60 mV)
Depolarisation due to sodium influx K
- 75 mV Na
repolarization due to potassium influx
closing of voltage-gated potassium channel
Electrotonic potential
Repolarisation due to potassium influx
Hyperpolarising afterpotential

29. The Action Potential threshold
Inactivation of voltage-controlled sodium channel
Equilibrium potential of sodium (+60 mV)
Opening of voltage-controlled sodium channel
Opening of voltage-controlled potassium channel
threshold
Electrotonic potential
Resting potential (-75 mV)
Hyperpolarization due to more outflux of potassium ions
Dentistry 07

30. The Action Potential (excitability changes)
Absolute refractory period
Relative refractory period
ENa (+60 mV)
Depolarisation (due to sodium influx)
Resting potential (-75 mV)
Polarized state (resting)
Hyperpolarising afterpotential
EK (-95 mV)

31. The Action Potential
threshold

36. neuron from the inferior olive