文档介绍：Chapter 4 Systemic circulation and
cardiovascular regulatory mechanism
§1 Electrical activity of the heart
I Electrical activity of the heart
1. working cell ()
(1) Resting potential (RP) ----- - 90 mV
Mechanism: K+ efflux
(2) Action potential (AP) (25min±)
Two concepts (Review)
◇ Threshold potential
◇ threshold (intensity)
1)Phase of AP
Phase 0
Phase 1
Phase 2
Phase 3
Phase 4
2) Ionic basis (20min±)
Phase Ionic basis
Phase 0 Na+ influx
Phase 1 K+ efflux
Phase 2 Ca2+ influx + K+ efflux
Phase 3 K+ efflux
Phase 4 sodium pump
2. SA cell = Pacemaker cell ( = 六版 P80 Fig .4-4 B ) (20min±)
AP -----Phase 0,3,4
Phase4------a fast spontaneous depolarization
(2) Ionic basis
3. Purkinje cell
(1)AP is quite similar to that of working cells except phase 4.
(2) Phase 4 ------- a spontaneous depolarization
Ⅱ Electrophysiological properties
1. Automaticity
(1) Exp.
(2) Concept:
 The automatic nature of the heartbeat is referred to as automaticity.
• Automaticity is due to the spontaneous electrical activity of the SA node.
(3) Specialized conducting system
From high to low rhythmicity, they are SA node, interatrial tract, internodal tract, atrial–ventricular node, intraventricular tracts and Purkinje cells.
the normal pacemaker of the heart ----- SA node
ectopic pace makers --------- Other regions of the heart
Part of the heart V m/S
Purkinje Fiber
Internodal tract
Ventricular muscle
Nodal area
(4) Mechanism: a spontaneous depolarization in Phase 4
ion basis : a progressive reduction in outward current of K+
2. Conductivity
conduction of cardiac impulse (pathway)
(2) atrioventricular delay
(3)Factors affecting conduction velocity
During different periods of the cardiac cycle, there are changes in excitability or the threshold of stimulation during a cardiac cycle. According to the excitability of the heart, a cardiac cycle can be divided into three periods.