electrical activity in a human heart?

Question

can someone describe the ionic basis of electrical activity in the heart???

thanx

Answer 1

Ions crossing in and out of the myocardial cells in a controlled fashion as the action potential moves through the heart causing contraction.

Na+, K+, Ca2+.

Answer 2

Cardiac electrical activity occurs with the establishment of a resting membrane potential and the stimulation of an action potential, much like in nerve cells.

Sodium/Potassium ATPase pump generates the resting membrane potential by pumping 3Na+ out of the cell and 2K+ into the cell. This establishes the Resting Potential

There is a tendency for the cells to leak and hence some Na+ escapes. This gradually raises the membrane potential until the threshold potential is reached. If the cell leaks slowly, then the cell will be stimulated by the conduction of the next action potential from a faster leaking cell (SA node usually being the fastest and hence being the "pacemaker" of the heart).

At a certain level of membrane potential, Voltage Gated Sodium Channels respond to a stimulus by allowing an influx of Na+ changing the resting potential and making it more positive.

Voltage Gated Calcium and Potassium Channels open when the peak level is reached. There is a brief "phase 1" drop in the membrane potential as the Sodium Channels close. Then the balanced movements of Ca++ and K+ ions cause a plateau phase ("phase 2").

Once the Ca++ channels close, the remaining K+ efflux lowers the membrane potential again as K+ leaks out ("phase 3").