1.3

Question 1

The … potential is created and maintained by sodium-potassium pumps and potassium ion channels in a neurone’s membrane.

Answer 1

resting

Question 2

Sodium-potassium pumps use active transport to move … sodium ions out of the neurone for every two potassium ions moved, ATP is needed to do this.

Answer 2

three

Question 3

Potassium ion channels allow facilitated … of potassium ions out of the neurone, down their concentration gradient.

Answer 3

diffusion

Question 4

The sodium-potassium pumps move sodium ions … of the neurone, but the membrane isn’t permeable to sodium ions, so they can’t diffuse back in.

Answer 4

out

Question 5

An … is created because there are more positive sodium ions outside the cell than inside

Answer 5

electrochemical gradient

Question 6

The sodium-potassium pumps also move … ions in to the neurone.

Answer 6

potassium

Question 7

When the cell’s at rest, most … ion channels are open. This means that the membrane is permeable to potassium ions, so some diffuse back through potassium ion channels.

Answer 7

potassium

Question 8

Even though positive ions are moving in and out of the cell, in total more … ions move out of the cell than enter. This makes the outside of the cell positively charged compared to the inside.

Answer 8

positive

Question 9

When a neurone is stimulated, sodium ion channels in the cell membrane open. If the stimulus is big enough, it’ll trigger a rapid change in potential difference. This causes the cell membrane to become …

Answer 9

depolarised

Question 10

Voltage-gated ion channels are channels that only … at a certain voltage.

Answer 10

open

Question 11

… - this excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This makes the inside of the neurone less negative.

Answer 11

Stimulus

Question 12

… - If the potential difference reaches the threshold (around -55mV), voltage-gated sodium ion channels open and more sodium ions diffuse into the neurone. This is positive feedback.

Answer 12

Depolarisation

Question 13

… - at a potential difference of around +30 mV the sodium ion channels close and voltage-gated potassium ion channels open. The membrane is more permeable to potassium so potassium ions diffuse out of the neurone down the potassium ion concentration gradient. This starts to get the membrane back to its resting potential. This is negative feedback

Answer 13

Repolarisation

Question 14

… - potassium ion channels are slow to close so there’s a slight ‘overshoot’ where too many potassium ions diffuse out of the neurone. The potential difference becomes more negative than the resting potential (i.e. less than -70 mV).

Answer 14

Hyperpolarisation

Question 15

… - The ion channels are reset. The sodium-potassium pump returns to its resting potential by pumping sodium ions out and potassium ions in, and maintains the resting potential until the membrane’s excited by another stimulus.

Answer 15

Resting potential

Question 16

After an action potential, the neurone cell membrane can’t be excited again straight away, because the ion channels are recovering and they can’t be made to open - sodium ion channels are closed during … and potassium ion channels are closed during hyperpolarisation.

Answer 16

repolarisation

Question 17

The refractory period acts as a time delay between one … and the next.

Answer 17

action potential

Question 18

The refractory period makes sure that action potentials don’t overlap but pass along as discrete …

Answer 18

impulses