The conductive system 1 Normal Impulse Conduction Sinoatrial

The conductive system: 1

Normal Impulse Conduction Sinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers

AUTOMATICITY & RHYTHMICITY Some cardiac fibers have the capability of self-excitation causing automatic rhythmical discharge and contraction. The fibers of the conducting system have this properties ventricular muscle fibers do not have prepotentials, and they discharge spontaneously only when injured or abnormal

Sinoatrial node SA node is called the pacemaker of the heart SA node is composed of a group of specialized cardiac muscle cells (have almost no contractile muscle filaments) Instead they are the cells that gained a property to generate spontaneous action potentials.

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The SA node is the normal pacemaker because it a) is the most rapidly discharging part b) is the most richly supplied by nerve endings c) is located in the atrium d) none of the above

generate spontaneous action potentials? REALLY? ? ? HOW? ? 9

Na+Ca++ K+ K+ Pacemaker cell f. TLK Ca ch Cach ch ch -40 -60 f ch 10

SUMMARY At -60 m. V (RMP ) At -50 m. V At -40 m. V (firing level) At +20 m. V f channels TCa channels First part of prepotential Second part of prepotential LCa channels Depol. K channels Repol. 11

intensité de courant current intensity 12

Sympathetic and parasympathetic innervation to the heart 14

PNS SA node • AV node • To lesser extent to atria • Very little to vent • SNS All parts of the heart • Strong representation to the • ventricular muscle 15

Effect of the sympathetic stimulation on the SA node Na NE Ca Na B 1 receotor Gs protean 16 Adenyl cyclase f channel Ca Ca channel

Effect of the parasympathetic stimulation on the SA node Ach Ca Ca K channels M 2 receptor Gs protean K 17 K Gi protean Adenyl cyclase Ca channel