Nerve Impulses

Question 1

when is a neurone in resting potential?

Answer 1

• the outside of the membrane is positively charged compared to the inside
• more positive ions on the outside of membrane = so the membrane is polarised
• voltage of the membrane at rest = resting potential

Question 2

how is resting potential created and maintained?

Answer 2

• sodium-potassium pumps and sodium ion channels in the neurones membrane

Question 3

what do the sodium-potassium pumps used?

Answer 3

active transport
- moves 3 sodium ions out of the neurone
- moves 2 potassium ions into the neurone
- this requires ATP

Question 4

what do the potassium pumps use?

Answer 4

they allow facilitated diffusion of potassium ions out of the neurone, down their concentration gradient

Question 5

explain how a resting potential is established?

Answer 5

• sodium potassium pumps move sodium ions out the neurone, but the membrane isn’t permeable to sodium ions, so they can’t diffuse back in
• this creates a sodium ion electrochemical gradient as there are more positive sodium ions outside the cell than inside
• the sodium-potassium pumps also move potassium ions in the neurone
• this means that the membrane is permeable to potassium ions, so some diffuse back out through potassium ion channels
• more positive ions move out of cell than enter, so makes the outside of the cell positively charged than the inside

Question 6

explain how an action potential is generated?

Answer 6

• neurone is stimulated, voltage gated sodium ion channels open
• if the stimulus is big enough, it’ll trigger a rapid change in potential difference
• this causes the cell membrane to become depolarised

Question 7

when does depolarisation take place?

Answer 7

when the sodium Ione channels open