The Passage Of An Action Potential

Front 1

What is an Action Potential?

Back 1

A short-term change in the electrical potential on the surface of an axon due to a stimuli: changes from -65megavolts to +40 megavolts inside the membrane.

Front 2

On what space does an action potential move once its been created?

Back 2

Rapidly

Front 3

Stage 1 of the passage of an action potential on unmyelinated axon.

Back 3

At resting potential the conc of sodium ions outside the axon is high compared to the inside, the potassium ions are high inside the membrane compared to the outside. There is more positive ions outside the membrane than there is inside. The axon membrane is POLARISED.

Front 4

What does it mean when is the membrane polarised?

Back 4

When there is more positive ions on the outside compared to the inside of the axon membrane.

Front 5

Stage 2 of the passage of an action potential on unmyelinated axon.

Back 5

A stimulus causes a sudden influx of sodium ions. This causes reversal charge on the axon membrane (-65 megavolts to +40 megavolts). This is the action potential and the membrane is depolarised!

Front 6

What is Depolarisation?

Back 6

When the outside is more negative relative to the inside of the axon membrane.

Front 7

Stage 3 of the passage of an action potential on unmyelinated axon.

Back 7

The localised electrical circuits established by the influx of sodium ions causes the sodium voltage gated channels to open a little further.This causes depolarisation. Behind this new region of depolarisation , the sodium voltage-gated channels close and the potassium ones open. Pottasium ions begin to leave the axon along their electrochemical gradient.

Front 8

Stage 4 of the passage of an action potential on unmyelinated axon.

Back 8

the action potential is spread across the axon the same way further along the axon. The movement of potassium ions out of the membrane has continued to the extent that the axon membrane behind the action potential has returned to its original charged state (- 65 megavolts inside and positive outside) it has been repolarised.

Front 9

What is repolarisation?

Back 9

When the axon membrane has returned to its original charges after being depolarised by the reversal of charges caused by a stimuli.

Front 10

Stage 5 of the passage of an action potential on unmyelinated axon.

Back 10

The repolarisation of the axon membrane allows sodium ions to be actively transported out , once again returning the axon to its resting potential in readiness for a new stimulus.

Front 11

What is a myelinated Axon?

Back 11

There is a fatty sheath of myelin around the axon.

Front 12

What's the purpose of this sheath of myelin?

Back 12

To act as an electrical insulator preventing potentials from forming.

Front 13

What are the gaps between the Schwann cells that surround the axon membrane?

Back 13

Nodes of Ranvier

Front 14

How can an action potential pass along the axon membrane when its fully covered by sheath of myelin?

Back 14

It can jump from gap to gap ( these points are called Nodes of Ranvier). this is called Salutatory conduction.

Front 15

What is meant by the tern "Salutatory conduction" ?

Back 15

When the Action Potential jumps from node Ranvier to node Ranvier because these are the only gaps where there is no sheath of myelin surrounding the axon preventing it from potentials.

Front 16

Instead of walking across the axon membrane if I jump how will this be to my advantage? ref to the Action potential.

Back 16

YOU will be able to move across faster. So the action potential is able to move across the axon membrane faster when it jumps from node to node.

Front 17

The action potential moves faster on a unmyelinated axon.true of false?

Back 17

False the action potential moves faster on a myelinated axon because instead of moving across through every gate of the unmyelinated axon because its got no sheath to hinder potential because its an electrical insulator. It can jump from nodes of Ranvier to node of Ranvier because these are gaps were there is no sheath.