Action Potentials of Cardiac Cells

Step 1 of AP of Autorhythmic Cells

Na+ continuously enter the cell and membrane potential moves towards the threshold value of -40mv

Step 2 of AP of Autorhythmic Cells

AP is generated when threshold is reached; fast Ca+ channels open and rapidly depolarizes the cell until it reaches +20mv

Step 3 of AP of Autorhythmic Cells

K+ channels open and repolarization occurs; Ca channels close

Step 4 of AP of Autorhythmic Cells

Temporary hyperpolarization and the cycle repeats

Step 0 of AP of Contractile Cells

ions depolarize the cell to its threshold value of -75mv

Step 1 of AP of Contractile Cell

Na+ channels open and cause rapid depolarization

Step 2 of AP of Contractile Cell

at +30mv Na channels close and Ca+ channels opens; Na and Ca cancel each other out as Na exits and causes plateau phase

Step 3 of AP of Contractile Cell

Ca channels close and K+ channels opens; repolarization occurs

What is causing the rapid depolarization stage of autorhythmic cells?

opening voltage regulated fast Ca++ channels

What is causing the rapid depolarization stage of contractile cells?

opening voltage regulated fast Na+ channels