5.2

Question 1

When a nerve impulse passes along a neurone changes occur in the

Answer 1

electrical charge across the plasma membrane of the neurone

Question 2

An influx of sodium ions into the sensory nerve ending causes its membrane to

Answer 2

depolarise and create a generator potential

Question 3

Once a generator potential exceeds a threshold value an

Answer 3

action potential is generated

Question 4

Neurone not carrying a nerve impulse is said to be at

Answer 4

rest

Question 5

Neurone at rest- the inside of the neurone is

Answer 5

negatively charged with respect to the outside

Question 6

The difference in charge (inside and outside neurone) is called the

Answer 6

resting potential

Question 7

Resting potential =

Answer 7

-70mV

Question 8

Several kinds of protein molecules in the neurone membrane:

Answer 8

sodium-potassium pum that uses ATP to pump 3 Na ions out of the cell in return for 2K ions

Sodium and potassium channels

Question 9

The inside of the neurone is negatively charged compared to the outside, when the neurone is at rest:

Answer 9

Negatively charged protein ions inside the cell which cannot pass through the plasma membrane

Sodium-potassium pump moves 3 Na ions out for every 2 K ions that are moved in - more positively charged ions outside the neurone than outside

Sodium channels are closed when the neurone is at rest, and only allow very limited diffusion of sodium ions back into the cell

Question 10

At rest the membrane is about 100 times more permeable to potassium ions than to

Answer 10

sodium ions when the neurone is at rest

Question 11

Sodium and potassium channels in the neurone membrane are open or closed depending on the potential difference or voltage across the membrane - therefore they are said to be

Answer 11

voltage-gated channels

Question 12

AP 1) Membran is at its resting potential -

Answer 12

sodium channels are all closed but some of the potassium channels are open

Question 13

AP 2) Depolarisation - the stimulus causes the membrane to depolarise -

Answer 13

the sodium channels are open, allowing sodium ions to diffuse into the neurone - these ions are positively charged so they cause the pd across the membrane to reverse

Inside the neurone now becomes positively charged compared to outside

Question 14

AP 3) Once some sodium ions enter this causes more sodium channels to open, allowing

Answer 14

more sodium ions to enter the neurone

Question 15

AP 4) Repolarisation - pd across the membrane has changed, the sodium channels close and potassium channels open -

Answer 15

potassium ions diffuse out of the axon

Question 16

AP 5) As potassium ions diffuse out of the axon, more potassium channels open -

Answer 16

this causes more potassium ions to diffuse out of the axon

Question 17

AP 6) so many potassium ions leave the neurone that there is a temporary ‘overshoot’ this is called

Answer 17

HYPERPOLARISATION

Potassium channels now close and the sodium-potassium pump restores the resting potential

Question 18

For a very short time after the sodium and potassium channels close, they are unable to open again due to the

Answer 18

change in shape of the proteins

Question 19

The inability to open again only lasts for a few milliseconds, but during this time the neurone cannot conduct another action potential known as the

Answer 19

refractory period

Question 20

The membrane of the neurone is unable to respond to a stimulus that would normally cause an

Answer 20

action potential