3.2 Resting and action potential

Question 1

What does the plasma membrane consist of?

Answer 1

• Phospholipid bilayer (impermeable to charged molecules)
• Intrinsic Na+ and K+ protein leak channels.
• Sodium-potassium pump.
• Na+ voltage gated protein channels
• K+ voltage gated protein channels

Question 2

What’s the membrane’s charge like during resting potential?

Answer 2

The potential difference (voltage charge) which exists across neurons. The membrane is said to be polarised (+ve on 1 side of membrane and -ve on the other side of the membrane).

Question 3

What is the voltage difference between inside and outside for a plasma membrane at resting potential?

Answer 3

65mV

Question 4

How is resting potential maintained?

Answer 4

By active transport and passive diffusion of ions. The neuron isn’t resting! No impulse (action potential) is being transmitted.

Question 5

Describe resting potential

Answer 5

• Higher Na+ concentration outside of cell than K+
• Higher K+ concentration inside of cell than Na+
• Membrane more permeable to K+ (as more K+ channels are open)
• Na/K pump actively transports 3Na+ out and 2K+ in

Question 6

What’s the name of the fluid inside and outside an axon?

Answer 6

Outside axon: extracellular tissue fluid
Inside axon:
Intracellular cytoplasm

Question 7

Sodium and potassium ions can only cross the axon membrane through proteins. Explain why. [2]

Answer 7

1. can’t pass through phospholipid bilayer;
2. because water soluble/not lipid soluble/charged

Question 8

Explain why energy is required in the maintenance of the resting potential in an axon. [2]

Answer 8

1. ATP / energy required by ion pumps
2. To move Na+ and K+ against concentration gradient

Question 9

What are the 5 stages of action potential?

Answer 9

• Resting potential
• Depolarisation
• Peak (action potential)
• Repolarisation
• Hyperpolarisation and refractory period

Question 10

What happens in the plasma membrane during resting potential?

Answer 10

• Voltage gated Na+ and K+ channels are closed

Question 11

What happens in the plasma membrane during depolarisation?

Answer 11

• Voltage gated Na+ channels open rapidly, resulting in movement of Na+ into the cell.

Question 12

What happens in the plasma membrane during action potential peak?

Answer 12

• Voltage gated Na+ channels begin to inactivate and voltage gated K+ channels begin to open.
• This initiates repolarisation.

Question 13

What happens in the plasma membrane during repolarisation?

Answer 13

With less Na+ moving to cell and more K+ out, membrane potential becomes more -ve, moving towards resting value.

Question 14

What happens in the plasma membrane during hyperpolarisation?

Answer 14

• Some voltage gated K+ channels remain open, resulting in movement of K+ out of the cell.

Question 15

What’s the threshold voltage value?

Answer 15

-55mV

Question 16

What is the voltage value of resting state?

Answer 16

-70mV

Question 17

What’s the voltage value of action potential peak?

Answer 17

30 - 40mV

Question 18

What is action potential caused by?

Answer 18

By stimulus arriving at the receptor, which leads to depolarisation.

Question 19

Depolarisation definition

Answer 19

A change in permeability of the membrane

Question 20

What’s the refractory period?

Answer 20

• During the refractory period after an action potential, a second action potential cannot be initiated
• The refractory period is a result of a temporary inactivation of the Na+ channels while the resting potential is restored.

Question 21

What’s meant by an all or nothing action potential response?

Answer 21

• An action potential only occurs when a cell reaches a threshold and the stimulus is large enough
• Action potentials occur completely or not at all
• A stronger stimulation doesn’t produce a stronger impulse
• Instead, a stronger stimulation produces a higher frequency of nerve impulses (more per sec)

Question 22

Describe the steps in an action potential

Answer 22

1. Open K+ channels create the resting potential & Na+/K+ pump
2. Activation gates of some Na+ channels open depolarising membrane to threshold value
3. Additional voltage-gated Na+ channels open, causing rapid spike of depolarisation & action potential
4. Na+ channels close; gated K+ channels open
5. K+ diffuses out, repolarising membrane & even hyperpolarising membrane
6. Cell returns to resting potential and it is restored via Na+/K+ pumps