action potential

Question 1

explain how an action potential is generated

Answer 1

• stimulus
  some Na+ voltage gated channel proteins open causing Na+ ions to move IN to cell
• depolarisation
  if “threshold” is reached around -55mV
  more Na+ channels open causing a large influx (movement) of Na+ ions down concentration gradient into cell = action potential
• repolarisation
  about 40 mV the Na+ channel proteins close and K+ voltage gated channel proteins open and K+ diffuses out of the axon down a electrochemical gradient membrane starts to return to resting state
• hyperpolarisation at around -80 mV
  K+ channels take time to close so K+ ions continue to diffuse out - causes the membrane potential difference to become more negative than resting potential
• resting potential is restored
  Na+/K+ pump and K+ channel proteins maintain resting potential around -65mV

Question 2

Define action potential

Answer 2

The potential difference across an axon membrane during depolarisation (inside +40mV compared with outside)

Question 3

Define depolarisation

Answer 3

Change in neurone membrane permeability causing a change in the distribution of ions (sodium ions enter making membrane potential +40mV)