Phase3: repolarization This proceeds more slowly than dose depolarization(phase 0). Phase 4: The interval from the completion of repolarization until the beginning of the next action potential Fast response 膜电位 AP 0 -80 b 4 ERP 100200300
Phase 3 ：repolarization This proceeds more slowly than dose depolarization (phase 0). Phase 4 : The interval from the completion of repolarization until the beginning of the next action potential
Action potential occurs well before the contractile force attains its peak, and repolarization is completed well before the cell reaches its full resting value. The relaxation of the cardiac muscle takes place mainly during phase 4 of the action potential Action potential Contractile force Time FIGURE 16-2. Relationships between the developed force and the changes in transmembrane potential in a thin strip of ventricular muscle.(Redrawn from Kavaler F, Fisher VI Stuckey JH: Bull N Y Acad Med 41: 592, 1965
Action potential occurs well before the contractile force attains its peak, and repolarization is completed well before the cell reaches its full resting value. The relaxation of the cardiac muscle takes place mainly during phase 4 of the action potential
There are two principal Types of Cardiac Action Potentials Fast-response action potentials: occurin atrial and ventricular myocardiac fibers and specialized conducting fibers(purkinje fibers) that exist mainly in the endocardiac surfaces of the ventricles Slow-response action potentials: occur in the sinoatrial (SA)node(sA), which is the natural pacemaker region of the heart and the atrioventricular(Av) node, which is the specialized tissue that conducts the cardiac impulse from he atria to the ventricles
• Fast-response action potentials: occur in atrial and ventricular myocardiac fibers and specialized conducting fibers (Purkinje fibers) that exist mainly in the endocardiac surfaces of the ventricles. • Slow-response action potentials: occur in the sinoatrial (SA) node (SA), which is the natural pacemaker region of the heart; and the atrioventricular (AV) node, which is the specialized tissue that conducts the cardiac impulse from the atria to the ventricles. There Are Two Principal Types of Cardiac Action Potentials
Comparing with the fast-response action potential: The resting membrane of slower-response is considerable less negative, a bout -50 mV The slop of the upstroke(phase 0), the amplitude and overshoot of the action potentials are less; (amplitude of action potential and the rate of rise of the upstroke are important determinants of the conduction velocity). 40 Fast response Slow response 0 2 -40 b c ERP RRP 120 ERP 0100200300 100200300 Time(msec)
Comparing with the fast-response action potential: The resting membrane of slower-response is considerable less negative, about -50 mV; The slop of the upstroke (phase 0), the amplitude and overshoot of the action potentials are less; （amplitude of action potential and the rate of rise of the upstroke are important determinants of the conduction velocity)
Fast responses may change to slow responses under certain pathological conditions, for example, in coronary artery disease A B C 0 mV K=3 mM K+=7 K+=10 50 msec E H 20 mV 0 mV St K+=14 K+=16 K+=3 FIGURE 16-3. Effect of changes in external [K+] on the transmembrane action potentials recorded from a Pur- kinje fiber The stimulus artifact (St)appears as a bipha- sic spike to the left of the upstro
Fast responses may change to slow responses under certain pathological conditions, for example, in coronary artery disease