Ünite 1: C1 Physiological Properties of Cardiac Muscle — Sınav Hazırlık Notları

• Pay close attention to the differences between fast-response and slow-response action potentials; remember that Phase 0 in fast-response is sodium-driven, while in slow-response it is calcium-driven.
• Do not confuse the mechanical and electrical functions of intercalated disks: desmosomes provide mechanical strength, while gap junctions provide electrical communication.
• Remember that the cardiac skeleton is a non-conductive barrier; the bundle of His is the only pathway for electrical signals to cross from the atria to the ventricles.
• Understand the mechanism of digitalis: it inhibits the Na+-K+ ATPase, which indirectly increases intracellular calcium by slowing down the NCX antiporter.
• Keep in mind that hyperkalemia increases (makes less negative) the resting membrane potential, which inactivates sodium channels and slows down depolarization.
• Note the dual sources of calcium in cardiac muscle: 30% is extracellular (trigger) and 70% is sarcoplasmic (primary). Without extracellular calcium, contraction cannot occur.