Human anatomy consist of many types of cells and among them, muscle cells play a pivotal functioning in the macro movements as well as in the movements which are performed at a micro level. Some movements are made voluntarily as in the limb movements whereas in others, the movements will occur involuntarily. In general, the muscles involved with voluntary movements are named as ‘striated muscles’ whereas the muscles that function involuntarily are named as ‘smooth muscles’. Apart from these two muscles, a third type also exists and would fall between the characteristics of both these muscles and at the same time they will be present only in a specific location. The location is the heart and the muscle type is therefore rightly named as the ‘cardiac muscles’.
The general information:
The cardiac muscles are located in the ‘myocardium’ or the muscle wall of the heart. Depicting its involuntary nature, the cardiac muscles will contract involuntarily as well as rhythmically in order to contract and relax the heart chambers and therefore propel blood from one chamber to another as well as to the outside organs. It will derive ample oxygen and blood supply through the coronary arteries and the blockage of which can be the underlying reason for the condition known as ‘angina’.
The muscle will have a structure made out of actin and myosin filaments and in places of overlapping of these filaments a phenomenon known as ‘stria’ can be seen and this is in par with the ‘striated muscles’ usually present in the muscles of the limbs. The arrangement of cardiac muscles would differ from the usual longitudinal arrangement of skeletal muscles due to the characteristic branching of these muscle cells.
The microscopic appearance of the cardiac muscles will differ in many ways from other types of muscle cells and is directly related to its structure. The branches of the cell will link up with the surrounding cardiac cells at the sites named as the intercalated disks and it would have a ‘step ladder’ appearance through microscopy. A single cell can intercalate with several surrounding cardiac cells but, these lines will travel only perpendicular to the direction of its muscle fibers.
The formation of intercalations or intercalated disks demarcates its functional adaptation for efficient transmission of the action potential, the signal that makes a muscle to contract, efficiently as well as effectively in order to produce a rhythmic contraction of the entire myocardium. This contraction will not take place all at once, but, along the path in which the action potential travels. This characteristic formation of muscle cells to form a network of cells is known as the formation of a ‘syncytium’.
Another important structural adaptation in a cardiac muscle is its relatively more efficient t-tubules that will allow the effective and rhythmic propagation of the action potential which is essential for smooth functioning of the entire myocardium.