how nerves work 4

Question 1

principle of how an action potential is propagated?

Answer 1

1- resting membrane potential.
2- flow of sodium ions into the axon membrane which increases the permeability of the membrane-more na flows in
3-if the membrane reaches a threshold of -55mv- membrane is depolarised and many Na+ flow in very quickly-membrane depolarises to +30mv
4- sodium channels close and potassium channels open. membrane become hyperpolarised
5-potassium channels close and membrane become repolarised to RMP

Question 2

why does repolarisation take longer than depolarisation?

Answer 2

the potassium channels open slower than the sodium channels

Question 3

what is the refractory period and what does it involve?

Answer 3

period in which no new action potential can be generated.
sodium channel has 2 gates. once first gate has opened and sodium has flown in it disactivates. the second gate then prevents the first gate being used again.
Absolute- no action potential can be generated no matter how greatly the axon is depolarised.

Question 4

properties of an action potential?

Answer 4

1- has a threshold value
2-uses VOLTAGE- gated ion channels
3-all or nothing principle
4-a stronger stimulus increases the frequency of Paps
5- has a refractory period– charge cannot flow backwards.
6-self-propagated: if one side of axon membrane becomes depolarised then it will cause sodium channels in next section to open and depolarise

Question 5

how to increase the speed of an action potential?

Answer 5

1- diameter of axon: lower axial resistance= depolarisation can spread out further more passively.
2- myelination: Schwann cells in the PNS and oligodendrites in the CNS wrap around the axon membrane.

Question 6

saltatory conduction

Answer 6

The folds in the membrane contain myelin which prevent charge from leaking out. sodium channels only present at nodes of ranvier so allows charge to spread between one node and the next without leaking out.

Question 7

Different types of axons.

Answer 7

if you were to consider the AP in a bundle of axons it would move at different speeds. this is because there are many different types of fibres. the overall AP is called the compound AP.
fastest fibres-associated with proprioception are the most sensitive to anoxia, least sensitive to local anaesthetics
slowest-associated with pain are the opposite.

Question 8

main differences between AP and generator potential?

Answer 8

1- AP not decremental-self propagates
2-AP based on voltage gated ion channels, generator of ligand-gated channels
3- AP has threshold
4-AP cannot summate
5- AP amplitude measured in frequency, generator in size
6- generator can be depolarising or hyper polarising
7-AP has refractory period