Download Heart Physiology

Heart Physiology Electrical events Se4ng the Basic Rhythm: •  The heart's (cardiac muscle) ability to depolarize and contract is intrinsic. •  Intrinsic cardiac conduc-on system – made up of autorhythmic cells conEnuously depolarize (a.k.a. driG towards threshold). •  Pacemaker poten3als – spontaneous change in membrane potenEals. –  The loss of K+ and the entry of Na+ depolarizes the membrane to the point of threshold (-­‐40 mV). –  Once threshold is reached, Ca2+ influx in the autorhythmic cells produces the acEon potenEal. LocaEon of Autorhythmic Cells: •  Sinoatrial (SA) node – pacemaker "sinus rhythm". •  Atrioventricular (AV) node •  AV Bundle •  Bundle branches •  Purkinje fibers Sinus Rhythm: •  Set by the SA node, the sinus rhythm is set at 75 impulses per minute. •  The total Eme of heart depolarizaEon from SA node to the last of the ventricular muscle is 2/10 second. •  Gap junc3ons connect the autorhythmic cells throughout the system. Extrinsic InnervaEon of the Heart •  Located in the medulla oblongata: –  Cardioacceleratory center (sympatheEc neurons) •  Norepinephrine –  Cardioinhibitory center (parasympatheEc neurons) •  actetylcholine Electrocardiograph “ECG” P wave = atrial depolarizaEon QRS complex = ventricle depolarizaEon and contracEon T wave = ventricle repolarizaEon P-­‐R interval = depolarizaEon through the enEre conducEon system Q-­‐T interval = ventricle depolarizaEon followed by ventricle repolarizaEon Defects in the ICS: •  Arrythmia: irregular heart rhythm. •  FibrillaEons: rapid and irregular contracEons. Normal ECG Extrasystole Heart Block FibrillaEon FibrillaEon