AP's in the heart- Myocytes

Modified Myocardial cells- generated their own action potentials

"Funny channels open in the membrane of myocytes

Na+ moves into the pacemaker cells

Causing the polarity to move from -60mV to -40mV (threshold)

At -40mV the Ca+ channels open causing Ca+ to move into the cell

Depolarisation

When the depolarisation peaks, K+ channels open.

K+ diffuses out of the myocyte.

Repolarisation

The action potential spreads to the cardiac muscle.

Sodium potassium pump restores it back to resting potential.

IN CARDIAC MUSCLE

Ca+ and Na+ travel through the gap junction of neighbouring cells.

Brings cells to threshold potential.

FAST Na+ channels open, causing rapid depolarisation.

SLOW Ca+ channels also open at -40mV. Adding to depolarisation.

Na+ channels shut, K+ channels open and Ca+ channels remain OPEN.

Early repolarisation

Depolarisation

There is a K+ and a Ca+ balance, where the amount leaving equals the amount entering.

Plateau Phase

HERE- Calcium is also released by the sarcoplasmic retinaculm.

Calcium caused calcium release.

Actin-myosin cross bridges formed.

Calcium gates then shut. K+ channels remain open.

Repolarisation

Sodium potassium pumps return concentrations to normal resting potential