What is the structure of cardiac muscle?

Cardiac muscle is a specialized type of muscle tissue found in the heart. The structure of cardiac muscle has distinctive features that enable it to perform its primary function, which is to contract and relax rhythmically in order to pump blood throughout the body.

Cardiac muscle has a striated appearance characterized by alternating dark and light bands. These striations result from the repetitive arrangement of contractile proteins within the muscle fibers. Cardiac muscle fibers are short, branched and interconnected, forming a three-dimensional network. 

Cardiac muscle cells contain T-tubules or transverse tubules, which are essentially invaginations of the cell membrane that penetrate deep into the cardiac muscle fiber. They connect to the sarcoplasmic reticulum, the storehouse of calcium ions that are necessary for muscle contraction.  

Intercalated discs are a unique structure found only in cardiac muscle tissue. These are specialized regions that connect adjacent cardiac muscles to each other. Intercalated discs contain two important structures – desmosomes and gap junctions. Desmosomes are protein complexes that hold the cardiac muscle fibers together, providing structural stability and preventing the cells from separating during contraction. Gap junctions are channels that ensure coordinated contractions by transferring electrical impulses between adjacent cardiac cells. 

Cardiac muscle cells have only one, centrally located nucleus.