Cardiac Muscles: It is also known as heart muscle, is the layer of muscle tissue which lies between the endocardium and epicardium. These inner and outer layers of the heart, respectively, surround the cardiac muscle tissue and separate it from the blood and other organs. Cardiac muscle is made from sheets of cardiac muscle cells. These cells, unlike skeletal muscle cells, are typically unicellular and connect to one another through special intercalated discs. These specialized cell junction and the arrangement of muscle cells enables cardiac muscle to contract quickly and repeatedly, forcing blood throughout the body.

Functions of Cardiac Muscles

• Cardiac muscles are the special tissues present only in heart of a human.
• Cardiac muscles help in pumping the blood at the time of involuntary movements of the body.
• Cardiac muscles are different from skeletal muscles in terms of the characteristic of controlling.
• It helps in having rhythmic contraction which is beneficial in having good blood flow in all parts of the body.
• It consists of cells that respond to the impulses of the nervous system.

Structure of Cardiac Muscles

The linked cardiac muscle cells, or fibres, provide strength and flexibility to cardiac muscle tissue.

• The cardiac muscle cells have one nucleus, but some have two. The nucleus contains all of the genetic material in the cell.
• Cardiac muscle cells also have mitochondria, which are referred to as “the powerhouses of the cell” by many. These are the organelles that convert oxygen and glucose into adenosine triphosphate energy.
• Under a microscope, cardiac muscle cells seem striated or striped. These stripes are caused by alternating filaments of myosin and actin proteins. 
• The dark stripes represent thick filaments made up of myosin proteins. Actin is found in thin or lighter filaments.
• When a heart muscle cell contracts, the myosin filament attracts the actin filaments, causing the cell to shrink. This contraction is powered by ATP in the cell.
• On either side, a single myosin filament joins two actin filaments. This results in a single piece of muscle tissue known as a sarcomere.
• Intercalated discs are structures that link cardiac muscle cells. Nerve signals are relayed from one cardiac muscle cell to another via gap junctions inside the intercalated discs.
• Desmosome is another type of structure seen in the intercalated discs. These aid in the bonding of heart muscle fibres.

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By Team Learning Mantras