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HEART PHYSIOLOGY
RHYTHMICAL EXCITATION OF HEART
By
Dr. Mudassar Ali Roomi (M.B;B.S, M.PHIL.)
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CONDUCTION SYSTEM OF HEART
SA node
Internodal pathways
AV node
AV bundle of His
Right and left bundle
branches
Purkinje fibers
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Conduction System
of the Heart SA node: sinoatrial node. Thepacemaker.
Specialized cardiac muscle cells.
Generate spontaneous actionpotentials (autorhythmic tissue).
Action potentials pass to atrial musclecells and to the AV node
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Conduction System
of the Heart
AV node: atrioventricular node.
Action potentials conducted moreslowly here than in any other part of
system.
Function: Ensures ventricles receivesignal to contract after atria havecontracted
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Conduction System
of the Heart
AV bundle: passes through hole incardiac connective tissue skeleton
to reach interventricular septum
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Conduction System
of the Heart
Right and left bundle branches:extend beneath endocardium to
apices of right and left ventricles
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Conduction System
of the Heart
Purkinje fibers:
Large diameter cardiac muscle cells withfew myofibrils.
Many gap junctions.
Conduct action potential to ventricular
muscle cells (myocardium) very rapidly
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Rate of impulse generation in heart:
SA NODE: 70-80/min
AV NODE: 40-60/min
AV BUNDLE, BRANCHES & VENTRICLES: 15-40/min
SA NODEnormal PACEMAKER
OTHERS ECTOPIC FOCI
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AV Node, and Delay of Impulse Conduction from the
Atria to the Ventricles
Locationof the A-V node:in the posterior wall of theright atrium immediatelybehind the tricuspid valve
there is a delay of 0.09second in the A-V node
A delayof another 0.04second occurs mainly in A-Vbundle
Thus, the total delay in theA-V nodal and A-V bundlesystem is about 0.13second.
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AV Node, and Delay of Impulse Conduction
from the Atria to the Ventricles
Cause of the Slow Conduction:
caused mainly by decreasednumbers of gap junctionsb/w successive cells in the
conducting pathwaysImportance of AV nodal delay:
this delay allows time forthe atria to empty theirblood into the ventriclesbefore ventricularcontraction begins.
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Rapid Transmission in the
Ventricular
Purkinje System
They are very large fibers, even
larger than the normal
ventricular muscle fibers
and they transmit action
potentials at a velocity of 1.5 to
4.0 m/sec, a velocity about 6
times that in the usual
ventricular muscle and 150 timesthat in some of the A-V nodal
fibers.
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Rapid Transmission in the
Ventricular
Purkinje SystemCause of rapid transmission:
The rapid transmission of actionpotentials by Purkinje fibers is
believed to be caused by a very
high level of permeability of the
gap junctions at the intercalated
discs between the successive
cells that make up the Purkinje
fibers.
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Rapid Transmission in the
Ventricular
Purkinje SystemFUNCTION: rapid transmission in
Purkinje fibers is responsible for
synchronous contraction of
ventricular muscle.
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Conduction velocities of hearttissues:
ATRIAL MUSCLE= 0.3m/sec
INTERNODAL PATHWAYS=
1m/sec AV NODE: slowest 0.05-
0.1m/sec
AV BUNDLE &BRANCHES/PURKINJE SYSTEM:
Maximum velocity= 1.5-4m/sec
VENTRICULAR MUSCLE=0.5m/sec
SUMMARY OF SPREAD OF THE CARDIAC IMPULSE THROUGH
THE HERAT
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ECTOPIC PACEMAKER OF HEART
Normal pacemaker of
heart?
Ectopic pacemaker?
Causes of ectopicpacemaker of heart?
1. Excessive excitability of
some part of the heartother than SA node
2. Heart blocks