Econ

Shamma Bhanvadia

Report 10

Question

Explain in detail the propagation of action potential in a cardiac cell.

There are five different phases to action potential propagation, ranging from phase 0 to phase 5.

The first phase is phase zero and it involves depolarization caused by sodium entering into the myocyte lasting about 2 msec.

The next step is early repolarization which when sodium channel begin to close making the cell slightly more negative than it was when sodium was flowing.

Afterwards is the plateau phase where calcium is constantly entering for about 200 msec making the cell extremely positive

Phase 3 is repolarization when the potassium channels open slowly bringing the cell back to its normal membrane potential.

The normal membrane potential in cardiac cells ranges form -85 to -95 mV

The last phase is phase 4 where the ion distribution is restored using the sodium/potassium pump.

Each phase correlates to the two phases of the cardiac cycle the systolic phase and the diastolic phase. The systolic phase is when the heart is contracting which occurs when calcium is released and that is described by the excitation contraction coupling steps.

How the heart contracts and works all depends on the initial propagation of the action potential.

The action potential starts the chain of events that leads to the large influx of calcium entering into the cell and once calcium is available to do its job it removes the inhibitory effect of the troponin-tropomyosin complex causing the thin filaments and thick filaments to contract.

After the heart and the cell contracts which all occurs at the same time because the heart cells act as a syncytium which means they all work together and what happens to one happens to all of them at the same time; after the contraction has ended the heart enters into the diastolic phase which is when the heart relaxes before the next contraction

During this phase of the cardiac cycle calcium is actively transported back into the...