Lesson 3

Question 1

Why is a neurone an excitable cell?

Answer 1

Because it can change its resting potential

Question 2

What is resting potential?

Answer 2

• The potential difference across the membrane when no nervous impulse is being conducted
• -70mV

Question 3

How to measure resting potential in experiments?

Answer 3

• Inserting microelectrodes into axons
• Measuring changes in electrical potential
• Read using cathode ray oscillope

Question 4

How is resting potential maintained?

Answer 4

• Large protein anions and organic phosphates (ATP4-) produce negative potential difference across membrane at -70mV
• Movement of sodium and potassium ions

Question 5

Describe movement of Na+ and K+ for resting potential

Answer 5

• Na+/K+ actively transport 3 Na+ ions out for every K+ in
• Some open voltage-gated K+ channels let K+ diffuse out
• Membrane more permeable to K+ because Na+ channels closed
• Some K+ channels allow K+ to leave axon via leakage

Question 6

What does stimulus do for depolarisation?

Answer 6

• Energy of stimulus causes some Na+ channels to open
• K+ channels close
• If threshold is reached, permeability to Na+ ions increases
• Membrane is depolarised when +40mV

Question 7

How does repolarisation occur?

Answer 7

• Na+ channels close and K+ channels open
• So K+ rapidly diffused out, reducing potential difference across membrane
• Overshoot in diffusion caused membrane to be hyperpolarised

Question 8

Describe the refractory period

Answer 8

• During this time, K+ and Na+ concs. return to resting potential levels
• Axon can’t transmit another impulse during this time