1. Resting Membrane Potential

2. Fig a,b

3. Types of Ion Channels

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

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

10. All or non law:
Application of a threshold stimulus either produces a full response or not at all.
Further increase in the intensity of a stimulus produces no increment or other changes in action potential.
The action potential failed to occur if the stimulus is sub-threshold, it produces only local changes with no propagation.
Latent period in a nerve: it is a period corresponding to the time taken from the site of simulation till the recording electrode.

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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)

21. Action Potential Propagation
Dentistry 07

22. Saltatory Conduction: Action Potential Propagation in a Myelinated Axon
Dentistry 07

23. Properties of action potentials
are all-or-none events
threshold voltage (usually 15 mV positive to resting potential)
threshold
-70
+60 mV
Stimulus
are initiated by depolarization
action potentials can be induced in nerve and muscle by extrinsic (percutaneous) stimulation –
APs do not summate - information is coded by frequency not amplitude.

29. Neuron
F8-2
Axons carry information from the cell body to the axon terminals.
Axon terminals communicate with their target cells at synapses.

31. Communication Between Neurons
Electrical synapse Chemical synapse
one-way conduction, always transmits signals in one direction.
this allows signals to be directed toward specific goals.

33. 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.

35. Graded Potentials
F8-9
Graded potentials are depolarizations or hyperpolarizations whose strength is proportional to the strength of the triggering event.
Graded potentials lose their strength as they move through the cell due to the leakage of charge across the membrane (eg. leaky water hose).

36. Graded Potentials Above Threshold Voltage Trigger Action Potentials
Graded potentials travel through the neuron until they reach the trigger zone. If they depolarize the membrane above threshold voltage (about -55 mV in mammals), an action potential is triggered and it travels down the axon.
F8-10

42. Spatial Summation
F8-12
A neuron may receive greater than 10, 000 inputs from presynaptic neurons.
The initiation of an action potential from several simultaneous subthreshold graded potentials, originating from different locations, is known as spatial summation.

43. Temporal Summation
F8-13
When summation occurs from graded potentials overlapping in time, it is called temporal summation.
Summation of graded potentials demonstrates a key property of neurons: postsynaptic integration.

44. Synaptic potentials
EPSP a IPSP

45. Synaptic potentials

46. Action Potential Propagation
Dentistry 07

47. Saltatory Conduction: Action Potential Propagation in a Myelinated Axon
Dentistry 07

50. Synaptic potentials
EPSP a IPSP