Download Intrinsic Conducting System

Intrinsic Conducting System
• Sinoatrial node.
– Electrical pace maker.
• Atrioventricular node.
– Receives impulses
originating from SA node.
• Bundle of His
– Electrical link between atria
and ventricles.
• Purkinje fibres.
– Distribute impulses to
ventricles.
•
The impulse-generating and impulse conducting
system of the heart comprises several specialized
structures whose coordinated functions act to
initiate and regulate the heartbeat.
1. The sinoatrial node, the “pacemaker” of the heart, is
located within the wall of the right atrium. It
generates impulses that initiate contraction of atrial
muscle cells; the impulses are then conducted to the
atrioventricular node. 70 - 80 impulse/min
2. The atrioventricular node is located in the wall of the
right atrium, adjacent to the tricuspid valve. 40 - 60
impulse/min
3. The Bundle of His is the band of conducting
tissue radiating from the AV node into the
interventricular septum where it divides into
two branches and continues as Purkinje
fibers. 30 - 60 impulses/min
4. Purkinje fibers are large, modified cardiac
muscle cells that make contact with other part
of the cardiac muscle. 15 - 40 impulses/min
The Conduction System
 Electrical impulses from your heart muscle (the myocardium) cause
your heart to beat (contract). This electrical signal begins in the
sinoatrial (SA) node, located at the top of the right atrium. The SA
node is sometimes called the heart's "natural pacemaker." When an
electrical impulse is released from this natural pacemaker, it causes
the atria to contract.
 The signal then passes through the atrioventricular (AV) node. The
AV node checks the signal and sends it through the muscle fibers of
the ventricles, causing them to contract.
 The SA node sends electrical impulses at a certain rate, but your
heart rate may still change depending on physical demands, stress,
or hormonal factors.
Cardiac Electro-Physiology
•
Phase 0: Rapid depolarisation of the cell membrane and it is associated
with
the
inflow of the Na+ ions.
•
Phase 1: A short initial phase of rapid repolarisation due to activation of
a Cl- current (inflow). K+ channel rapidly open and close causing a transient outward
current.
•
Phase 2: Action potential plateau. A period of more gradual repolarisation in which
there is a movement of Ca2+ ion into the cell.
•
Phase 3: Final repolarisation. A second period of rapid repolarisaion during which K+
move out of the cell.
•
Phase 4: A fully repolarised state during which K+ channel opens. K+ move into and
Na+ out of the cell again to enable the next cycle to begin.
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0
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2
3
4