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HEART PHYSIOLOGYRHYTHMICAL EXCITATION
OF HEARTBy
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.
The pacemaker. Specialized cardiac muscle
cells. Generate spontaneous action
potentials (autorhythmic tissue).
Action potentials pass to atrial muscle cells and to the AV node
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Conduction System of the
Heart
AV node: atrioventricular node. Action potentials conducted
more slowly here than in any other part of system.
Function: Ensures ventricles receive signal to contract after atria have contracted
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Conduction System of the
Heart
AV bundle: passes through hole in cardiac 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 with few 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 Location of the A-V
node: in the posterior wall of the right atrium immediately behind the tricuspid valve
there is a delay of 0.09 second in the A-V node
A delay of another 0.04 second occurs mainly in A-V bundle
Thus, the total delay in the A-V nodal and A-V bundle system is about 0.13 second.
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AV Node, and Delay of Impulse Conduction from the Atria to the
VentriclesCause of the Slow
Conduction: caused mainly by
decreased numbers of gap junctions b/w successive cells in the conducting pathways
Importance of AV nodal delay:
this delay allows time for the atria to empty their blood into the ventricles before ventricular contraction 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 times that 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
action potentials 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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SUMMARY OF SPREAD OF THE CARDIAC IMPULSE THROUGH THE HERAT
Conduction velocities of heart tissues:
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
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ECTOPIC PACEMAKER OF HEART
Normal pacemaker of heart?
Ectopic pacemaker?Causes of ectopic
pacemaker of heart?
1. Excessive excitability of some part of the heart other than SA node
2. Heart blocks