15.3- PASSAGE OF AN ACTION POTENTIAL

Question 1

What do action potentials do once it has been created?

Answer 1

move rapidly along axon

Question 2

How does the size of an action potential change from one end of an axon to the other?

Answer 2

action potential remains the same from one end of axon to other

Question 3

When one region of axon produced an action potential and becomes depolarised, what does it act as for the next region of the axon?

Answer 3

acts as stimulus for depolarisation of next region of axon

Question 4

What is the action potential? (hint- wave)

Answer 4

travelling wave of depolarisation

Question 5

What does the previous region of the membrane return to when the next region is depolarised?

Answer 5

returns to resting potential, undergoes repolarisation

Question 6

At resting potential what is the concentration of sodium ions and potassium ions outside the axon membrane like?

Answer 6

conc. of sodium ions outside axon membrane high relative to insides

potassium ions high inside membrane relative to outside

Question 7

At resting potential, what is the overall concentration of positive ions like?

Answer 7

overall conc. of positive ions greater outside, making positive compared with inside
axon membrane polarised

Question 8

What does a stimulus cause the influx of and what does this do?

Answer 8

cause sudden influx of sodium ions + hence reversal of charge on axon membrane
this is the action potential + membrane depolarised

Question 9

What does the localised electrical currents established by the influx of sodium ions cause?

Answer 9

opening of sodium voltage-gated channels a little further along axon
resulting influx of sodium ions in this region causes

Question 10

What happens behind the new region of depolarisation?

Answer 10

sodium voltage-gated channels close + potassium ones open

potassium ions begin to leave axon along their electrochemical gradient

Question 11

What does the repolarisation of the axon allow for? (hint- sodium ions)

Answer 11

allows sodium ions to be actively transported out, once again returning the axon to its resting potential in readiness for a new stimuli if it comes

Question 12

In myelinated axons, what does the fatty sheath of myelin around the axon act as?

Answer 12

electrical insulator- preventing action potentials from forming

Question 13

What is the size of the intervals that break the myelin insulation?

Answer 13

1-3mm

Question 14

What are the intervals of 1-3mm that break the myelin insulation called?

Answer 14

nodes of Ranvier

Question 15

what can occur at the nodes of Ranvier?

Answer 15

action potentials

Question 16

How do action potentials travel through a myelinated axon?

Answer 16

jump from node to node

Question 17

What is the process of action potentials jumping from node to node in a myelinated axon known as?

Answer 17

saltatory conduction

Question 18

Does an action potential pass along a myelinated or unmyelinated axon of the same diameter faster?

Answer 18

faster through myelinated

Question 19

Why does an action potential pass along an unmyelinated neurone slower than a myelinated neurone?

Answer 19

events of depolarisation have to take place all the way along an axon + this takes more time in unmyelinated