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Lecture 2

KINESIOL 1AA3 Lecture 2: Cardiac Muscle Tissue & Conduction System

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McMaster University
Kim Dej

1/22/2017 12:01:00 AM Cardiac Muscle Tissue • Elongated, branching cells containing 1-2 centrally located nuclei, contains actin and myosin • Intercalated disks: thickening of sarcolemma containing • Desmosomes: hold fibers together • Gap junctions: aid in conduction of muscle action potentials, allow atria/ventricles to contract as one unit Autorhythmic Fibers • Autorhythmic fibers: heart fibers repeatedly generate action potentials that trigger heart contractions, have two important functions • Pacemaker potential: spontaneously developing local potential, results in generation of action potentials in SA node • Form cardiac conduction system: group of autorhythmic cardiac muscle fibers that generate and distribute electrical impulses to stimulate coordinated contraction of the heart chambers; includes SA node, AV node, AV bundle, right and left bundle branches, Purkinje fibers Skeletal vs. Cardiac Muscle Physiology 1. Action potential conduction • Cardiac: conducted cell to cell • Skeletal: conducted along length of single fiber 2. Action potential propagation • Cardiac: slow because of gap junctions and small fiber diameter • Skeletal: faster due to larger fiber diameter 3. Calcium release • Cardiac: calcium induced calcium release (CICR) • Skeletal: movement of calcium through plasma membrane and t tubules into sarcoplasm, stimulates release of calcium from sarcoplasmic reticulum 1/22/2017 12:01:00 AM SA Node: Sinoatrial node, 100 bpm • Location: right atrial wall, inferior and lateral to opening of superior vena cava • Description: do not have stable resting potential, repeatedly depolarize to threshold spontaneously, where heartbeat originates • Function: spontaneous depolarization is pacemaker potential, triggers action potential, propagates throughout atria via ga
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