Passage of an action potential

Aim: To understand how nerve impulses are

propagated along a neurone

Recap of action potential

“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

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

Passage of an action potential along an unmyelinated axon

• Stimulus received

• Influx of sodium ions

• Membrane depolarised – action potential started

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

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

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.