Flashcards in Passage Of An Action Potential Deck (12):
How does the action potential move along the axon?
The reversal of electrical charges that are reproduced at different points along the axon membrane
How are the action potentials regenerated along each small region of the axon membrane?
As one region of the axon produces an action potential and becomes depolarised, it acts as a stimulus for the depolarisation of the next region of the axon
What is the movement of a action potential sometimes compared to?
A Mexican wave
Outline the first stage of the passage of an action potential along an unmyelinated axon?
At resting potential the concentration of sodium ions outside the axon membrane is high relative to the inside, whereas that of the potassium ions is high inside the membrane relative to the outside. The axon membrane is polarised.
Outline the second stage
A stimulus causes a sudden influx of sodium ions and hence a reversal of charge on the axon membrane. This is action potential and the membrane is depolarised
Outline the third stage
The localised electrical circuits established by the influx of sodium ions causes the opening of sodium voltage-gated channels which causes depolarisation. Behind this region of depolarisation, the sodium voltage-gated channels close and the potassium ones open and the potassium ions begin to leave the axon
Outline the fourth stage
The action potential (depolarisation) is propagated in the same way further along the axon. The outward movement of the potassium ions has continued to the extent that the axon membrane behind the action potential has returned to its original charged state (It has been repolarised)
Outline the fifth and final stage?
The repolarisation of the axon allows sodium ions to be actively transported out, once again returning the axon to its resting potential in readiness for a new stimulus
In myelinated axons, what is the purpose of the fatty sheath?
It acts as an electrical insulator that prevents action potentials from forming
At what points on a myelinated axon can action potentials occur?
The nodes of Ranvier
How are action potentials transferred along a myelinated axon?
They travel via localised circuits between adjacent nodes of Ranvier and the action potentials effectively 'jump' from node to node in a process known as saltatory conduction