DOH100 Lecture Notes - Lecture 3: T Wave, Qrs Complex, Sinus Rhythm
Document Summary
Explain how the sa node fires spontaneously and rhythmically. Set by sa node at 60-100 bpm. Ectopic foci - region of spontaneous firing. Nodal rhythm set by av node at 40-50 bpm. Intrinsic ventricular rhythm 20-40 bpm if damage to sa and av node. Sa node has no stable resting membrane potential due to leaky na+ ion channels. Instead has pacemaker potential, gradual depolarisation from -60mv due to slow influx of na+ Occurs at threshold -40mv with depolarising phase to 0mv. Fast ca2+ channels open with ca2+ in. Repolarising phase at -60mv k+ channels close and pacemaker potential starts over. At rest sa node fires at 0. 8sec, i. e. 75 bpm. Describe the action potentials of cardiac muscle and relate to function. Plateau - 200 to 250 msec sustains contraction. Ca2+ binds to fast ca2+ channels on sr. Releases more ca2+ into cytosol - contraction. Long plateau means ventricles can fill with blood before contraction.
