Action Potentials

Question 1

What does depolarization mean?

Answer 1

The membrane potential becomes less negative (or even positive)

Question 2

What does hyperpolarization mean?

Answer 2

The membrane potential becomes more negative.

Question 3

what two factors effect the change in membrane potential (depolarization or hyperpolarization)?

Answer 3

• the direction of the movement of ions

- the charge carried by the ion.

Question 4

What two components make the electrochemical gradient?

Answer 4

Concentration gradient + chemical charge gradient

Question 5

What direction of flow does Na+ take?

Answer 5

inwards (into membrane)

Question 6

What direction of flow does K+ take?

Answer 6

Outwards (out of cell)

Question 7

What is the equation for the driving force?

Answer 7

Vm - Eion

Question 8

Does opening of Na+ channels cause hyperpolarization or depolarization?

Answer 8

Depolarization.

Question 9

Does opening of K+ channels cause hyperpolarization or depolarization?

Answer 9

Hyperpolarization.

Question 10

What is the difference between leak channels and gated channels?

Answer 10

Leak channels are always open whereas gated channels open in response to stimulus

Question 11

What are the three states of voltage-activated Na+ channels?

Answer 11

• Open
• closed
• Inactivated

Question 12

Describe the neuronal action potential pathway employing the appropriate terms.

Answer 12

• At resting potential
• reaches threshold
• upstroke is the depolarisation
• overshoot is when its at its peak
• downstroke is the repolarisation
• undershoot is when it slightly hyper polarises before returning to resting potential.

Question 13

What is conductance?

Answer 13

Conductance is a measure of conductivity; a ratio of the current flow to the difference in potential in what it is flowing through.

Question 14

How long does an action potential last?

Answer 14

2-3 milliseconds

Question 15

What type of feedback is seen when Na+ channels are activated?

Answer 15

Positive feedback

The activation of one channel cause further channels to open and continues depolarisation.

Question 16

What type of feedback is seen when K+ channels are activated?

Answer 16

Negative feedback

Outward movement of K+ causes depolarisation which turns off the stimulus for opening.

Question 17

Describe what refractory period means.

Answer 17

When voltage-gated Na+ channels enter their inactive state, waiting for repolarisation to occur to then generate another action potential.

Question 18

What is the difference between the absolute and relative refractory period?

Answer 18

Absolute refractory period- no stimulus can elicit a second action potential (all channels inactivated)

Relative refractory period- A stronger stimulus may elicit a second action potential (some channels activated, some inactivated)

Question 19

Where is the action potential initiated?

Answer 19

Axon Hillock.

Question 20

Once active potential has been initiated at the axon hillock, further trigger stimuli are required to pass impulse down the nerve. True or false?

Answer 20

False.

Question 21

What are the two methods used to pass impulse down nerve through propagation?

Answer 21

Contiguous conduction and saltatory conduction.

Question 22

Describe contiguous conduction.

Answer 22

• occurs in unmyelinated fibres
• Like a Mexican wave
• The parts of the axon that are at resting potential before reaching the action potential, they must be depolarised first by the current flow between the activated adjacent area to the resting area.
• The action potential at the end is identical to the one at the start

Question 23

Describe saltatory conduction.

Answer 23

• occurs in myelinated fibres
• the action potential jumps over nodes
• current flow comes from adjacent nodes
• much quicker than contiguous conduction.

Question 24

What are nodes of Ranvier?

Answer 24

areas where there isn’t myelin sheath covering it (exposed to ECF)