1. Passage of an action potential
Aim: To understand how nerve impulses are propagated along a neurone

2. Recap of action potential

3. “Movement” of an action potential
Once an action potential has been created it passes down the axon
The initial action potential and depolarisation of the membrane stimulates an action potential in the next region of the axon
Reversal of charge across the membrane is reproduced along the axon

4. Passage of an action potential along an unmyelinated axon
Resting potential:
High Na+ concentration outside
High K+ concentration inside
Inside negative relative to outside
Axon membrane polarised

5. Passage of an action potential along an unmyelinated axon
Stimulus received
Influx of sodium ions
Membrane depolarised – action potential started

6. Passage of an action potential along an unmyelinated axon
Localised electrical circuits form
Influx of sodium causes opening of sodium voltage-gated channels further along

7. Passage of an action potential along an unmyelinated axon
Action potential propagated along the neurone.
Areas that have become depolarised become repolarised due to movement of K+ outside of the membrane
Sodium-potassium pump starts back up returning membrane to resting potential

8. Passage of an action potential along a myelinated axon
Fatty sheath of myelin around axons act as insulator preventing action potentials forming.
Breaks in sheath (called nodes of Ranvier) at intervals of 1-3mm
Action potentials occur at these points and jump from node to node. This process is called saltatory conduction. This speeds up the passage of the action potential.