Nerve Impulses

Question 1

What is resting potential?

Answer 1

-At rest the neurone has a potential of-70mV
-There are more positive ions on the outside of the cells than inside
- The sodium/potassium pump in moving 3+ sodium ions out and K+ potassium ions in by active transport

Question 2

What is depolarisation?

Answer 2

• Sodium channels open due to stimulus
• Membrane becomes more permeable to sodium
• Sodium diffuses in the cell through sodium ion channels down its gradient
• Inside of the cell becomes more positive
• When threshold potential of -50mV is met, more voltage gated sodium ion channels open
• Further depolarisation occurs to +40mV more sodium ions are going to diffuse in

Question 3

What is repolarisation?

Answer 3

• At section potential of +40mV voltage-gated Na+ channels close
• Voltage-gated K+ channels open
• Membrane becomes more permeable to K+
• K+ diffuses out of the cell down electrochemical gradient
• Inside of the cell becomes more negative

Question 4

What is hyperpolarisation?

Answer 4

• Voltage gated K+ channels close at resting potential -70mV
• BUT close slowly so reporlarisation goes beyond resting potential

Question 5

What happens when it returns to resting potential?

Answer 5

• Sodium potassium pump restores neurone to resting potential
• Moves sodium and potassium ions against their concentration gradients
• 3 Na+ are pumped out and 2 K+ are pumped in
• The 3:2 ratio gives a more positive charge on the outside compared to inside