Describe the Contraction and Relaxation of Cardiac Muscles (Essay Sample)

CONTRACTION AND RELAXATION OF CARDIAC FIBERS
Contraction and relaxation of cardiac fibers
The cardiac sarcomere is the fundamental contraction unit in the heart. This is a well formed and structured cytoskeleton made of actin, myosin and regulatory proteins (Ebashi, 2007). The myosin and actin are also referred to as the thick and the thin filaments respectively. Myosin acts as the protein motor in the cardiac muscle cells which directly convert chemical energy into mechanical energy. Essentially, the contractions of myocytes are brought about by the shortening and lengthening of the macromere. The chemical and physical interaction of the actin and myosin is responsible for the lengthening and the shortening f the macromere. All of these processes are as a result of the relaxation contraction process in the cardiac muscle cells. The myosin-actin interaction forms the basis of the sliding filament theory used to explain the contraction of cardiac muscles. Variation of the length of the macromere regulates the contractile force of the heart.
The relaxation and contraction of the cardiac fiber is a complex physiological process. the process is characterized by rapid depolarization and polarization due to the inflow and outflow of ions along the trans-membrane channel. The cardiac muscle fibers undergo coordinated contraction via calcium-induced calcium release process conducted through the intercalated discs.
Cardiac muscles are striated and contain highly developed tubule systems in addition to the thick and thin filaments. Comparatively, the sarcoplasmic reticulum of the cardiac muscles is less developed as compared to the skeletal muscles. Contractions and relaxations of these muscles are based on a mechanism that leads to the sliding of the thin and thick filaments. Contraction is initiated by the development of membrane action potential. The action potential causes an increase of calcium ions in the myofilaments. The increased concentration causes the activation of the myosin-ATPase which in turn leads to the sliding of the thin and thick filaments CITATION Fra121 \l 1033 (Frank, 2012). Most of the calcium ions that lead to the contraction process emanate from the extracellular source since the poorly developed sarcoplasmic reticulum of the cardiac muscles cannot give enough calcium ions. An influx of extracellular calcium ions through the calcium channels on the tubules sustains the depolarization of the cardiac muscle for a longer time.
The physiology of the cardiac muscles is by various cells. These include; the sinoatrial node, the ventricular and antiventricular node, atrium and bundle of His. Cardiac muscles are categorized into two main categories namely; the contractile cells and the auto-rhythmic cells. The cells develop different types of action potential when stimulated. Auto-rhythmic cells are specialized cells found in the cardiac muscles only. These cells make it possible for the cardiac fiber to initiate contractions without needed for innervations. Contractile cells are the ones responsible for the contraction of the cardiac fibers in response to signals from the cardiac nodes. Unlike the former, contractile cells contract upon stimulation.
Contractile cells form a majority of the cardiac muscle cells and they ...