HEART2UPDATE - Aorta Superior vena cava Right pulmonary...

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Figure 18.4e (e) Superior vena cava Right pulmonary artery Pulmonary trunk Right atrium Right pulmonary veins Fossa ovalis Pectinate muscles Tricuspid valve Right ventricle Chordae tendineae Trabeculae carneae Inferior vena cava Aorta Left pulmonary artery Left atrium Left pulmonary veins Pulmonary valve Aortic valve Mitral (bicuspid) valve Left ventricle Papillary muscle Interventricular septum Myocardium Visceral pericardium Endocardium
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4.2.4 Compare the physiological properties of cardiac muscle fibers with those of skeletal muscle cells Cardiac Muscle shorter, fatter single or double nuclei intercalated disks (desmosomes, gap junctions) = interdependence functional syncytium 20-40% of volume is mitochondria myofibril diameters vary & much branching gives indistinct striations fewer T-tubules; less elaborate Ca ++ delivery less developed sarcoplasmic reticulum almost exclusively aerobic metabolism abundance of fuel type determines fuel used Skeletal Muscle longer, cylindrical multinucleate structural independence; motor unit grouping functional independence 2-5% of volume is mitochondria uniform myofibrils give distinct striations many T-tubules; complex Ca ++ delivery complex sarcoplasmic reticulum readily uses anaerobic metabolism intensity determines fuel type used J. Carnegie, UofO
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4.2.4.2 describe intercalated discs and relate 2 aspects of their structure to the support of cardiac function J. Carnegie, UofO Intercalated discs: (i) desmosomes for strong cell-cell adhesion during contraction (ii) gap junctions for electric coupling »» functional syncytium Fig. 18.11
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Cardiac Muscle Contraction • Cardiac muscle contraction is similar to skeletal muscle contraction • Heart muscle differs in that: – Is stimulated by nerves and is self-excitable (automaticity) – Contracts as a unit – Has a long (250 ms) absolute refractory period
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4.2.5 Compare the electrical properties of contractile cardiac muscle cells with those of autorhythmic cardiac muscle cells heart contraction stimulated by action potentials: action potential = signal; muscle twitch = response Fig shows action potential of ventricular Purkinje fibers ( remember AP of neuron is 1-2 msec); total sequence = about 300 msec 4.2.5.2 special characteristics of cardiac muscle cells 1) All-or-none law: applies to organ rather than individual cells 2) Stimulation: autorhythmicity of (1%) cardiac cells 3) Absolute refractory period: 250 msec vs 1-2 msec for action potential stimulating skeletal muscle – Why is this important? **prevents tetanic contraction!!**
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Phase 1 = depolarization due to Na + influx (positive feedback) Phase 2 = plateau maintained by Ca 2+ influx (“slow” Ca 2+ channels) Phase 3 = repolarization with K + efflux 18.12 (7 th edition) J. Carnegie, UofO Fig 18.12
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absolute refractory period almost = muscle twitch  allows heart to fill again heart needs to be stimulated in just one location; whole organ responds
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This note was uploaded on 12/21/2010 for the course ANP ANP1105 taught by Professor Kowalovski during the Fall '08 term at University of Ottawa.

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HEART2UPDATE - Aorta Superior vena cava Right pulmonary...

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