1.1. Physiologic Anatomy of Cardiac Muscle

• What are the three major types of cardiac muscle?

  Atrial muscle, ventricular muscle, specialized fibers
• How do atrial and ventricular muscles contract compared to skeletal muscle?

  They contract similarly but last longer
• Why do specialized excitatory and conductive fibers contract feebly?

  They contain few contractile fibrils
• What do specialized fibers exhibit in terms of electrical activity?

  Automatic rhythmical electrical discharge
• What is the role of specialized fibers in the heart?

  They control the rhythmical beating of the heart
• What is the histological structure of cardiac muscle?

  • Cardiac muscle fibers arranged in a latticework
  • Fibers divide, recombine, and spread
  • Striated like skeletal muscle
  • Contains actin and myosin filaments
• How do actin and myosin filaments in cardiac muscle compare to those in skeletal muscle?

  They are almost identical in structure
• What are intercalated discs in cardiac muscle?

  Cell membranes separating individual cardiac cells
• What is the function of gap junctions at intercalated discs?

  Allow rapid diffusion of ions
• How do action potentials travel in cardiac muscle?

  They travel easily from cell to cell
• What is a syncytium in the context of cardiac muscle?


  A network of interconnected cardiac muscle cells
• How many syncytiums does the heart have?

  Two syncytiums
• What are the two syncytiums in the heart?

  Atrial syncytium and ventricular syncytium
• What separates the atria from the ventricles?

  Fibrous tissue surrounding A-V valvular openings
• How are potentials conducted from the atrial syncytium to the ventricular syncytium?

  Through the A-V bundle of conductive fibers
• What is the significance of the atria contracting before the ventricles?

  It enhances the effectiveness of heart pumping