Origin and spread of cardiac impulse, pacemaker, conducting system of heart, its importance
-
Upload
rajesh-goit -
Category
Health & Medicine
-
view
3.986 -
download
2
Transcript of Origin and spread of cardiac impulse, pacemaker, conducting system of heart, its importance
RK Goit, LecturerDepartment of Physiology
Origin & Spread of Cardiac Impulse, Pacemaker, Conducting System of Heart, its Importance
• parts of the heart normally beat in orderly sequence
• contraction of the atria (atrial systole) is followed by contraction of the ventricles (ventricular systole)
• during diastole all four chambers are relaxed
• heartbeat originates in a specialized cardiac conduction system & spreads via this system to all parts of the myocardium
Tissue Conduction rate (m/s)SA node 0.05Atrial muscle 0.3Atrial pathways 1AV node 0.05Bundle of His 1Purkinje system 4Ventricular muscle 0.3-0.5
The Sinus Node as the Pacemaker of the Heart• SA node discharge at an intrinsic rhythmical rate of 70-
80/min (AV nodal fibers 40-60/min, & Purkinje fibers 15- 40/min
• each time the SA node discharges, its impulse is conducted into both the A-V node & the Purkinje fibers
• SA node discharges again before either the A-V node or the Purkinje fibers can reach their own thresholds for self-excitation
• the sinus node controls the beat of the heart
Abnormal Pacemakers—“Ectopic” Pacemaker• occasionally some other part of the heart develops a
rhythmical discharge rate that is more rapid than that of the sinus node
• a pacemaker elsewhere than the sinus node is called an “ectopic” pacemaker
• an ectopic pacemaker causes an abnormal sequence of contraction of the different parts of the heart
• another cause of shift of the pacemaker is blockage of transmission of the cardiac impulse from the sinus node to the other parts of the heart
Important functions:• pacemaker– setting the rhythm of electrical excitation that causes
contraction of the heart
• conduction system– ensures that cardiac chambers become stimulated to contract
in a coordinated manner, which makes the heart an effective pump
References
• Ganong Review of Medical Physiology, 23/E• Textbook of Medical Physiology, 12/E Guyton & Hall • Understanding Medical Physiology, 4/E Bijlani &
Manjunatha
Thank You