5: Action potentials

Question 1

What is depolarisation?

Answer 1

Membrane potential becomes LESS NEGATIVE or even positive

Question 2

What is repolarisation?

Answer 2

Membrane potential becomes MORE NEGATIVE

Question 3

The movement of ___ across membranes causes changes in membrane potential

Answer 3

ions

Question 4

In which direction do Na⁺ ions move?

Answer 4

Into the cell

Question 5

In which direction do K⁺ ions move?

Answer 5

Out of the cell

Question 6

When sodium channels open, the membrane potential (repolarises / depolarises).

Answer 6

depolarises

As E_Na+ = +60 mV

Question 7

When potassium channels open, the membrane potential (repolarises / depolarises).

Answer 7

repolarises

As E_K+ = -90mV, membrane potential tends towards -90mV - membrane may even hyperpolarise beyond its normal value of -70mV

Question 8

What are two common gated ion channels?

Answer 8

Voltage-gated ion channels - open depending on membrane voltage

Ligand-gated ion channels - open upon binding of certain ligands

Question 9

If a membrane depolarises, it’s probably due to the influx of which ion?

Answer 9

Na⁺

Question 10

If a membrane repolarises or hyperpolarises, it’s probably due to the efflux of which ion?

Answer 10

K⁺

Question 11

What is an action potential?

Answer 11

Short-term reversal of membrane potential

Question 12

Which cells make use of action potentials to communicate?

Answer 12

Nerve cells

Question 13

Action potentials are only generated when a ___ is reached and cannot be stopped after they are triggered. What kind of reaction is this?

Answer 13

threshold

all-or-nothing reaction (like swallowing)

Question 14

The initial activation of Na⁺ channels in an action potential causes more Na⁺ channels to open. Which kind of feedback mechanism is this?

Answer 14

Positive feedback

Question 15

The activation of K⁺ channels causes repolarisation, which in turn switches K⁺ channels off. What kind of feedback mechanism is this?

Answer 15

Negative feedback

Question 16

In an action potential, ___ channels open first, then ___ channels open with a slight delay.

Answer 16

Na⁺ first

K⁺ after a delay

Question 17

Na⁺ channels open in response to depolarisation by positive feedback.

What happens to them during sustained depolarisation?

Answer 17

They become inactivated (NOT closed) and are unable to provide passage for Na⁺

Question 18

What closes Na⁺ channels following their inactivation?

Answer 18

Repolarisation by K⁺ efflux

Question 19

What are the three states of Na⁺ channels, and during which stages of an action potential do they present?

Answer 19

Open state during depolarisation

Inactivated state after maintained depolarisation

Closed state after repolarisation

Question 20

Which state of Na⁺ channel is responsible for the refractory period?

Answer 20

Inactivated state

Question 21

What is the refractory period?

Answer 21

Time between action potentials

Question 22

What material increases the resistance of axons to current leak and therefore increases conduction speed?

Answer 22

Myelin

Question 23

How does current spread in unmyelinated axons?

Answer 23

Passively