Topic overview

Start with the big picture

Cardiomyocytes are striated, branched cells joined at intercalated discs. Gap junctions support electrical coupling, while desmosomes help maintain mechanical attachment, allowing the tissue to function as a coordinated syncytium. The lesson follows the electrical sequence from pacemaker activity through action-potential phases and the prolonged refractory period, then explains how calcium entry triggers calcium release from the sarcoplasmic reticulum. Calcium removal supports relaxation, while preload, afterload, and autonomic input shape contraction. The broader lesson also connects cardiac muscle physiology to energy metabolism, calcium regulation, hormonal modulation, cardiac-cycle phases, systolic function, wall stress, and responses to injury. Together, these topics provide a framework for understanding how cardiac muscle sustains continuous, rhythmic work.