Final answer:
The myocardium is composed of striated cardiomyocytes, which are involuntary muscle cells with intercalated discs unique to the cardiac muscle of the heart.
Step-by-step explanation:
The myocardium is composed of a specific type of muscle cells known as cardiomyocytes. These cells form the cardiac muscle found exclusively in the heart. Unlike smooth muscle cells which are not striated, cardiomyocytes, similar to skeletal muscle cells, are striated due to the presence of sarcomeres that give them a striped appearance.
However, cardiac muscle is distinct because it contains unique structures called intercalated discs, which allow for synchronized contraction vital for heart function. Cardiac muscles are also classified as an involuntary muscle, as they operate without conscious control, in contrast with skeletal muscles which are also striated but are voluntary.