Understanding Cardiac Physiology: Heart's Electrical & Contractile Mechanisms - Prof. Char, Study notes of Biology

Download Understanding Cardiac Physiology: Heart's Electrical & Contractile Mechanisms - Prof. Char and more Study notes Biology in PDF only on Docsity! 19 September 28 MC 2 short answer Cardiac Myocyte Sliding filament mechanism T tubules extend from sarcolemma and permit extracellular ions and fluid to diffuse near intracellular structures Sarcoplasmic reticulum stores substantial amounts of Ca++ which is released when ryanodine receptors are stimulated by extracellular Ca++ which flow through L type voltage sensitive dihydropyridine receptors Calcium induced calcium release Ryanodine receptors – activated by calcium, initiate calcium release Intercalated discs allow low resistance for charge to flow from cell to cell Ca++ enters cytoplasm via VG L-type Ca++ channels which interact with ryanodine receptors on SPR (“trigger calcium”). Calcium induced calcium release. Ca++ released from sequestered Ca++ Tropomyosin is associated with three regulatory proteins: TN-T, TN-C, and TN-I Ca++ binds to TN-C which in presence of ATP changes conformation of troponin Myosin and actin cross-bridge when myosin binding sites exposed on actin SERCA-resequesters Ca++ via phosphorylation of phospholamban (SERCA = SPEndoreticulum CaATPase) Calsequestrin is the primary calcium storage protein in the SR. It binds to approximately 50 Ca++ ions per molecule during diastole which prevents Ca++ precipitation. Ca++ releases from TN-C and inhibition of binding sites occurs → relaxation ATP needed for contraction and relaxation (lusitropy) Conduction Pathways SA node → atrial muscle → AV node → bundle of His → right and left bundle branches → Purkinje fibers → ventricular muscle Delay at AV node Most of end-diastolic volume reaches the ventricles due to the pressure difference rather than atrial contraction SA node generates fastest signal (60/min) Generation gets slower farther down the chain SA node, while functional, overrides the others SA node does not have resting membrane potential Action Potential Conduction IAB = (VA – VB) / RAB IAB – current between cells A and B V – voltage R – resistance Depolarizing current or + charges Current flows from depolarized to hyperpolarized within cell Ion causing rapid upswing of action potential Ventricular muscle – sodium