[15.2-3] the nerve impulse, passage of an action potential

Question 1

what can a nerve impulse be defined as?

Answer 1

a self-propagating wave of depolarisation that travels along the axon membrane

Question 2

what is resting potential?

Answer 2

• difference in charge between inside of neurone and outside of neurone when it is at rest ie. no nerve impulse being carried
• ~70 mV

Question 3

describe the charges found in the axon

Answer 3

• axon is more negatively charged inside relative to outside as it has more positively charged ions outside axon than inside
• Na+ outside, K+ inside
• ratio of 3Na+: 2K+

Question 4

how is the movement of ions across the axon membrane controlled?

Answer 4

• PLB of axon plasma membrane prevents Na+ and K+ ions diffusing across it
• sodium / potassium-gated channel proteins so those ions can be moved by FD sometimes but not always
• if channels remain open, ions can move freely through FD
• sodium-potassium pump proteins in axon membrane actively transport K+ in and Na+ out of the axon

Question 5

what determines whether a VGS/KCP will be opened or closed?

Answer 5

• voltage changes in the local area of that particular channel protein
• once impulses are sent, some of neurone is at RP, but others are in AP

Question 6

moving from resting potential to action potential

Answer 6

1. stimulus from receptor causes VGSC in membrane to open
2. Na+ can enter axon via FD
3. charge inside axon is increased until a peak of ~+40 mV is reached

Question 7

what is polarised?

Answer 7

when axon is at resting potential

Question 8

what is depolarised?

Answer 8

when axon is at action potential

Question 9

what is re-polarised?

Answer 9

when axon goes from resting to action and back to resting

Question 10

what is hyperpolarised?

Answer 10

when axon is even more polarised than usual

Question 11

passage of an action potential along a myelinated axon

Answer 11

• APs can occur in nodes of ranvier as they are the only points ions can and have to cross the membrane
• nerve impulses can jump from node to node via saltatory conduction (small ‘jumps’)
• speed of conduction is faster than in unmyelinated neurone
• when unmyelinated, depolarisation events, opening channel proteins, takes more time