Cardiac Physiology The heart: chambers, the valves Cardiac muscle cells Some cardiac muscle cells are autorhythmic Arrangement of cardiac muscle cells Excitation-contraction coupling

Atrioventricular (AV) Valves guard the passageway between the atria and the ventricles Tricuspid valve between right atrium and right ventricle Bicuspid (mitral) valve between left atrium and left ventricle

Semilunar valves Between ventricles and arteries Pulmonary valve between right ventricle and pulmonary artery Aortic valve between left ventricle and aorta

All myocardial cells Gap junctions at intercalated discs, waves of depolarization spread from one cell to another

Autorhythmic myocardial cells (pacemakers) are small myocardial cells with few contractile fibers Spontaneously generate action potentials Enables the heart to contract without any outside signal The heart is myogenic: signal for contraction originates from heart muscle itself

Most myocardial cells Remaining myocardial cells are striated Have sarcomeres Much smaller than skeletal muscle fibers Connected by gap junctions at intercalated discs Lots of mitochondria Lots of blood flow to myocardial cells

More facts about myocardial cells Large branching t-tubules Sparse sarcoplasmic reticulum Source of Ca++ is largely extracellular

Excitation-contraction coupling Depolarization cell membrane voltage gated Ca++ channels open  Ca++ enters cell  calcium-induced calcium release: Ca++ released from SR  Ca++ binds to troponin contraction

Myocardial cell relaxation Ca++ dissociates from troponin  Ca++ returns to SR by Ca++ ATPase  Ca++ also transported from cell by Na+-Ca++ indirect active transport protein: Ca++ is exchanged for Na+, which moves in along its electrochemical gradientNa+ removed by active transport