Cardiac

Cells

Cardiac muscle fibers have striations. These are created by the dark and light banding of the myofibrils packed into the cells. They are just like skeletal muscle fibers and can be easily confused for skeletal muscle.  There is a subtle difference between the squished appearance of the darkly-stained nucleiClusters of neurons in the CNS responsible for processing information. of skeletal and cardiac muscle fibers. The nuclei of skeletal muscle fibers appear more flattened than the nuclei of cardiac muscle fibers. The main differentiating characteristic is the intercalated discs that are perpendicular to the sarcolemma of the cardiac muscle fibers.

Intercalated Discs

Cardiac muscle fibers have intercalated discs.  These are where two adjacent cells come into contact.  An intercalated disc consists of desmosomes and gap junctions.  A desmosome is a very firm connecting proteinsLarge molecules made of amino acids with various functions in the body. between the two cells.  A gap junction is a little channel that allows these cells to exchange cytoplasmThe gel-like substance within a cell that contains organelles and cytosol..  When one of these cells has an action potentialA rapid, temporary electrical charge that travels along neurons, allowing signal transmission., it shares that electrical currentThe flow of electrical charge, as in ions moving across a neuron’s membrane. with the adjacent cell. The current travels via the gap junction.  Immediately following the current, the first cell contracts.  This contract also moves the adjacent cell, since they are attached.  This lets the heart squeeze blood through it. It’s similar to how you would squeeze a tube of toothpaste to expel that last little bit.