1. Chapter 10: Rhythmical Excitation of the Heart
Unit Three: The Heart
Chapter 10: Rhythmical Excitation of the Heart
Guyton and Hall, Textbook of Medical Physiology, 12th edition

2. Rhythmic Excitation
Specialized Excitatory and Conductive System
Sinus (Sinoatrial node)-located in the wall of the
right atrium and has almost no contractile muscle
filaments
Automatic rhythmicity-cardiac fibers with the ability
of self-excitation

3. Fig. 10.1 Sinus node and the Purkinje system of the heart

4. Rhythmic Excitation (cont.)
Mechanism of Sinus Nodal Rhythmicity
Fig Rhythmical discharge of a sinus node fiber

5. Rhythmic Excitation (cont.)
Lesser negativity since the cell membranes are
naturally leaky to Na+ and Ca++
Have the three types of channels
Fast sodium
Slow sodium-calcium
Potassium
At -55 mV the fast Na+ channels may be inactivated
Only the slow channels open
The AP is therefore slower to develop

6. Self-Excitation of Sinus Node Fibers
Internodal Pathways and Transmisson of the Impulse
AV Node and Delay of Impulse
Cause of slow conduction
Ventricular Purkinje System and Distribution of
Fibers
One-way Conduction Through the AV Bundle (His)

7. Fig. 10.4 Transmission of the cardiac impulse through the heart, showing
the time of appearance in different parts of the heart.

8. Control of Excitation and Conduction in the Heart
Sinus Node as the Pacemaker of the Heart
Abnormal Pacemakers (Ectopic)
Role of the Purkinje System
Parasympathetic and Sympathetic Control
Vagal effects
Sympathetic stimulation
Mechanism of the sympathetic effect