The cardiac cycle

Question 1

describe the process of ionic conductances in ventricular muscle cells 1

Answer 1

1. voltage gated sodium channels open

Question 2

2

Answer 2

2. na+ inflow depolarises the membrane and triggers the opening of still more na+ channels, creating a positive feedback cycle and a rapidly rising membrane voltage

Question 3

3

Answer 3

3. na+ channels close when the cell depolarises and the voltage peaks at nearly +30mV

Question 4

4

Answer 4

4. ca2+ entering through slow calcium channels prolongs depolarisation of membrane, creating a plateau
   - plateau falls slightly because of some k+ leakage, but most k+ channels remain closed until end of plateau

Question 5

5

Answer 5

5. ca2+ channels close and ca2+ is transported out of cell

- k+ channels open, and rapid k+ outflow returns membrane to its resting potential