Some smooth muscle may have pacemaker potentials, slow cyclic self generated depolarization that may bring the cell to threshold. Thus they contract as a unit. Cardiac muscle Cardiac muscle has similarities to both sk and sm. Because it is striated, cardiac muscle is most akin to sk muscle. High number of capillaries and mitochondria.
Fibers are shorter than sk muscle are electrically linked by gap junction at the intercalated disk.
EC - coupling is similar to sk muscle because of organization of contractile elements. Cardiac cells can be divided into two subdivision. Conducting cells - Have pacemaker potentials a prepotential that brings about an action potential. These cells lack a substantial K conductance and have a high Na permeability, that tends to keep it rather depolarized. K channels are open 2.