Cardiac Muscle

Cardiac muscles are the muscles of the heart. They are self-contracting, autonomically regulated and must continue to contract in rythmic fashion for the whole life of the organism. Hence they have special features.

The cells are Y shaped and are shorter and wider than skeletal muscle cells. They are predominatly mononucleated. The arrangement of actin and myosin is similar to skeletal striated muscle.

Some of the cardiac muscle cells are auto-rhythmic, i.e they contract even in the absence of neuronal innervation (known as pacemaker cells). Intercalated disks are located between cardiac muscles cells. These contain gap junctions which provide communicating channels between cells.The intercalated disks allows waves of depolarisations to sweep across the cells thus synchronising muscle contraction.

Depolarisation of cardiac muscle cells differs from that of other muscle cells.Repolarisation takes much longer to occur and thus cells cannot be stimulated at high frequency. The advantege is that cardiac muscle are prevented from going into tetanus.