L4 - Action Potentials

Question 1

If a mystery ion with a positive charge has an equilibrium potential of -60mV and membrane potential is -70mV, then the ion will…

Answer 1

have net movement into the cell

Question 2

If a mystery ion with a positive charge has an equilibrium potential of -60mV and membrane potential is -40mV, then the ion will…

Answer 2

have net movement out of the cell

Question 3

Does an upward deflection result in a decrease in membrane potential or an increase?

Answer 3

decrease in membrane potential

Question 4

Does a downward deflection result in a decrease in membrane potential or an increase?

Answer 4

increase in membrane potential

Question 5

What is hyperpolarization?

Answer 5

when the membrane potential becomes more negative at a particular spot on the neuron’s membrane

Question 6

What is depolarization?

Answer 6

when the membrane potential becomes more positive

Question 7

What is repolarization?

Answer 7

when the membrane potential begins to move back towards its resting voltage

Question 8

What is a graded potential change?

Answer 8

a change in the membrane potential relative to the resting potential

Question 9

If the membrane of a neuron suddenly became more permeable to Na+, what would happen to membrane potential?

Answer 9

it depolarises

Question 10

During a triggering event, what happens to the resting potential of a neuron if there is only one Na+ voltage gated ion channel?

Answer 10

the active area will be depolarised by a graded potential and this depolarisation will spread in both directions towards inactive areas of the neuron
however if there is only one Na+ voltage gated ion channel the charge will be lost over the course of the neuron

Question 11

What is the threshold voltage?

Answer 11

the voltage required to change the shape of the voltage gated sodium ion channel and initiate an action potential

Question 12

What is required to open the voltage-gated sodium channel?

Answer 12

the threshold voltage

Question 13

What are the two gates found on the voltage-gated sodium channel and what do they do?

Answer 13

the activation gate opens very fast, and the inactivation gate closes slowly resulting in a period of time when sodium can pass through
the inactivation gate closes at the peak of the action potential

Question 14

What is the positive feedback cycle of Na+ channels?

Answer 14

triggering event -> depolarisation (decreased potential) -> opening of some voltage-gated Na+ channels -> influx of Na+ (which further decreases membrane potential) -> depolarisation (decreased potential)

Question 15

How does the voltage-gated potassium channel repolarise the cell membrane?

Answer 15

at threshold voltage the activation gate opens very slowly and once it is completely opened potassium is able to very quickly leave the cell and repolarise the membrane (negative charge)

Question 16

What is the after-hyperpolarization period caused by?

Answer 16

the slow closing of the voltage gated potassium ion channel

Question 17

If a person’s ECF K+ concentration increases then neurons will be ____________ to fire an action potential

Answer 17

more likely

Question 18

If the voltage-gated potassium channels were removed from a neuron, would it be able to repolarise after an action potential?

Answer 18

yes, just more slowly

Question 19

Ouabain, a specific inhibitor of the Na+-K+-ATPase, is applied to a neuron. The next action potential that fires after ouabain application will appear…

Answer 19

the same as normal because Na+-K+-ATPase does not exchange enough Na+/K+ ions to make a difference

Question 20

What allows for the conduction of an action potential?

Answer 20

the charge of an active area at peak of action potential spreads out over the cell membrane resulting in the voltage gated sodium channels of inactive areas being activated (reaching their threshold voltage) which results in these areas reaching peak of action potential which continues the cycle

Question 21

Can a neuron fire off another action potential during an absolute refractory period? Why?

Answer 21

no, because this is the period of time when the voltage gated sodium channels are open or resetting back to their original conformation

Question 22

Can a neuron fire off another action potential during a relative refractory period? Why?

Answer 22

yes, but it is relatively difficult because we are further away from threshold voltage (as a result of hyperpolarization), therefore harder to create an action potential (bigger stimulus is required)

Question 23

Why is the absolute refractory period important in the physiology of firing off action potentials?

Answer 23

prevents backward current flow and the re-excitement of previous active areas which have been returned to RMP

Question 24

What determines the conduction velocity of a neuron?

Answer 24

the diameter of the axon (larger = faster) and whether it is myelinated or not

Question 25

What is the name of the gaps between two layers of myelination on an axon?

Answer 25

nodes of Ranvier

Question 26

Is the movement of ions that causes an action potential active or passive?

Answer 26

passive

Question 27

Why is an action potential faster in axons of larger diameter?

Answer 27

this is because there is less resistance to current flow

Question 28

How does myelination allow an action potential to move more quickly?

Answer 28

myelin insulates the axon, prevents ion leak and allows the action potential to jump from node to node all the way down the axon (avoids having to activate voltage gated sodium ion channels all the way down the neuron)

Question 29

What is the name for the movement of an action potential down a myelinated axon?

Answer 29

saltatory conduction

Question 30

What is the point of having different conduction velocities in different neurons?

Answer 30

so that action potentials can reach their target at the same time