, AV junctions! tissue, bundle of His and its branches. Purkmje's fibers),

musculature virtually becomes b syncytium Nerve and blood supply to the heart have been described later in this book Fig 51 9 SUMMARY & HIGHLIGHTS Myocardial cells (= fibers) are of 2 types, (i) Pace maker and conducting cells (= SAN, AV junctions! tissue, bundle of His and its branches. Purkmje's fibers), they generate impulse and conduct the impulse, (ii) Working myocardial cells (WMC), which contracl WMC consists ol myofibmls, each m/ofibnl consists ol 4 types of myofilaments. (i) acltn ii) myosin (iii) tropomyosin, and (iv) troponm At rest, the active sites of aclin (where myasin heads are To be aitached during contraction), are covered by iropomyosn 2 types of tubules are seen in sarrnlernma (= cell membrane of muscle fiber), (i) T tubules which communicate with the ECF, and; (ii) L tubules (= sarcoplasrnic reticulum) which do not communicate with the extenor T lubuias occur near the Z lines (which form the boundaries of sarcomere) and neat them L tubules form cisterns (or triads) 1 Introduction 2 Mechanical Properties (a) Mechanism of shortening (b) excitation corrtradron coupling fc) Force of contraction 3 Eleclncal Properties (a) Rhythmicily (I)Site of gene ration of impulse, (ii) Mechanism ol spontaneous generation of the rhythm {b) Conductivity (l)Spread of excrtation over Ihe atna; (it) Conduction through the ventricles fin) Slannius ligature Re-entry (c) Eicriabilily (I) Refractory penods (a) absolute, (b) relative, (13 Action potential of the heart muscle 4 Effects of ions on the electrophysiologica] properties of the heart muscle; various synthetic solutions Introduction According to Ihe traditional teaching, the basic properties of heart muscles are (i) ability I contracl, (ii) excitability, fiii) rhythmicrty (also called autorhythmicity). and (iv) conductivity Of these properties. the ability lo contract is a mechanical property whereas others are electrophysiotogical properties In short, cardiac muscle properties belong lo two groups (i) mechanical and (iij electrophysiological. THE MECHANICAL PROPERTIES The basic mechanical properly of the heart muscles is Ihat il can contract Contraction may or may not cause, shortening Neverthless, all contractions generate force and produce squeeze on the blood in venincular or atna! cavities which in turn, ultrnately speaking, causes ejection of blood from these cavities The major issues, discussed in this book, under the mechanical properties, are : (a) mechanism of shortening (b) excitation contraction coupling