cardiac action potentials

Question 1

describe the ventricular action potential

Answer 1

0 - 1 - 2 - 3 - 4
- resting membrane potential, 4 - sodium and calcium channels are closed, the potassium channels keep the MP at -90mV
- rapid depolarisation, 0 - sodium influx through open fast sodium channels
- early repolarisation, 1 - transient potassium channels open and potassium leaves which returns MP to 0mV
- plateau, 2 - influx of calcium ions through l type calcium channels, electrically balanced by potassium efflux
- repolarisation, 3 - calcium channels close by potassium channels remain open, return to -90mV
- return to 4

Question 2

describe sino atrial node action potential

Answer 2

0 - 3 - 4

• 0, voltage gated calcium ions channels open and calcium ions enter the cell
• 3 - voltage gated potassium channels open, potassium leaves cell, calcium channels close
• 4 - voltage gated potassium channels close, sodium slowly enters through leaky sodium channels until the threshold of -40mV is met