Cardiac Muscle Definition
Cardiac muscle, also known as myocardium, is a specialized type of muscle tissue that makes up the thick middle layer of the heart. It is one of three types of muscle in the body, along with skeletal and smooth muscle.
Cardiac muscle is involuntary and striated, meaning it has alternating light and dark bands under a microscope. It is responsible for the ability of the heart to pump blood throughout the body.
Cardiac Muscle Structure
Cardiac muscle tissue, also known as myocardium, forms the bulk of the heart and is a three-layered structure with a thick layer of myocardium sandwiched between two thin layers of the epithelium. Cardiac muscle cells or cardiomyocytes are striated, branched, and under involuntary control.
Each myocyte is a tubular structure composed of chains of myofibrils that consist of repeating sections of sarcomeres, which are the fundamental contractile units of the muscle cells. The sarcomeres contain specialized protein contractile fibers of actin and myosin that slide past each other to cause contraction.
Cardiac muscle cells are roughly rectangular in shape and measure 100-150μm by 30-40μm. They are joined at their ends by intercalated discs to form long fibers. Cardiac muscle cells contain many mitochondria which provide the energy needed for the cell in the form of adenosine triphosphate (ATP), making them highly resistant to fatigue.
T-tubules are microscopic tubes that run from the cell surface to deep within the cell. They are continuous with the cell membrane and open at the cell surface to the extracellular fluid surrounding the cell. T-tubules in cardiac muscle are bigger than those found in skeletal muscles and play an important role in excitation-contraction coupling.
The development of cardiac muscle cells begins after the formation of the linear heart tube. The heart tube undergoes looping morphogenesis, forming four chambers: left atrium, right atrium, left ventricle, and right ventricle. During this process, cardiac progenitor cells differentiate into cardiomyocytes through a series of complex molecular events.
The function of Cardiac Muscle
The cardiac muscle, also known as the myocardium, is a specialized type of muscle tissue that forms the heart. It is responsible for the contractility of the heart and, therefore, the pumping action.
The main function of the myocardium is to facilitate the contraction and relaxation of the heart walls in order to receive and pump blood into systemic circulation. The myocardial cells provide a scaffold for heart chambers and conduct electrical stimuli.
The movements that cardiac muscle tissue produces are involuntary, meaning they are automatic and cannot be controlled by a person. Unlike skeletal muscle tissue present in arms and legs, cardiac muscle cells perform highly coordinated actions that keep the heart pumping and blood circulating throughout the body.
Cardiac muscle cells form a highly branched cellular network in the heart. They are connected end to end by intercalated disks and are organized into layers of myocardial tissue that are wrapped around the chambers of the heart.
The contraction of individual cardiac muscle cells produces force and contributes to the Z line, which has a characteristic cross-striated pattern similar to that seen in skeletal muscle.
Cardiomyopathy is a disease that affects cardiac muscles. It causes fatty infiltration in cardiac muscle tissue in some cases or amyloid proteins collect and form deposits in other cases. These deposits cause the stiffening of ventricle walls which reduces its ability to pump blood out of it.
