Physiology 3120 Lecture Notes - Lecture 29: Purkinje Fibers, Atrioventricular Node, Heart Valve
15 May 2018
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Lecture 29 – Conducting System of the Heart
- SA node is located at the posterior wall of the right atrium (top of the right atrium)
- AP is generated at the SA node and it travels to the left atrium so it contracts at the same
time as the right atrium
- Interatrial myocardial band rapidly propagates the AP to the top of the left atrium
- AP from the atria enters the atrial contractile cells
- Atrial contractile cells are joined by intercalated disks that contain gap junctions
- Gap junctions allow the AP to travel from contractile cell to contractile cell
- AP starts at the top of both atria and propagates downwards
o Direction that the AP propagates is the direction that the cells contract in
o Cells contract from the top down
o = pushes blood through the AV valve and into the ventricles
- The way the AP propagates is the way the muscle contracts
- DO NOT want AP to propagate directly into the ventricular contractile cells from the atria
o If it did, the ventricles would contract from the top down
o = must stop the AP because want the ventricles to contract from the bottom up
- Atrioventricular ring is a bundle of fibrous CT that electrically isolates the atria from the
ventricles so that the AP cannot directly propagate into the ventricles
o Stops AP from going directly from the atria to the ventricles
- AP is transmitted from the SA node into the AV node through the intermodal pathway
- AV node SLOWS DOWN the AP to ensure the atria contract before the ventricles contract
o If they contracted at the same time, the heart would not be an efficient pump
- From the AV node, AP enters the Bundle of His
- Bundle of His is a rapid conducting system that propagates the AP to the apex of the heart
o Divides into two branches (left and right bundle branch) which travel down the
interventricular septum
- AP is now at the apex of the heart but it is not at the ventricular contractile cells yet
- From bundle of His, the AP enters the purkinje fibers
- Purkinje fibers rapidly conduct the AP to the ventricular contractile cells
- AP travels from the apex and travels upwards through the gap junctions of the ventricular
contractile cells
- Ventricles contract from the bottom up and push blood up and out through the valves
- Conducting system of the heart is highly coordinated or else the heart will not function as a
pump
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- AP propagation and conduction velocity of the AP differs in different parts of the heart
- Conduction velocity is distinct from generation of the AP – SA node generates the AP the
fastest but AP propagation through the SA node is fairly slow
- AP enters the atrial muscle and is conducted through gap junctions from cell to cell
- The AV node slows down the AP to ensure atria finish contracting before the ventricles do
- Bundle of his transmits the AP down to the apex of the heart very quickly
- Purkinje fibers VERY RAPIDLY transmit the AP to the ventricular contractile cells
- Ventricular muscle cells propagate the AP cell to cell through gap junctions
- AP is slow in some places and fast in other places
- SA node is the natural pacemaker (intrinsic rate is 100 times/min)
- Without input, the intrinsic (natural) rate – rate at which it spontaneously generates APs –
is 100 times/min
- Resting heart rate is 70 bpm (there is influence that influences the intrinsic rate at rest)
o PSYN keeps the heart rate at a lower rate than it wants to be
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lecture 29 conducting system of the heart. Sa node is located at the posterior wall of the right atrium (top of the right atrium) Ap is generated at the sa node and it travels to the left atrium so it contracts at the same time as the right atrium. Interatrial myocardial band rapidly propagates the ap to the top of the left atrium. Ap from the atria enters the atrial contractile cells. Atrial contractile cells are joined by intercalated disks that contain gap junctions. Gap junctions allow the ap to travel from contractile cell to contractile cell. The way the ap propagates is the way the muscle contracts. Do not want ap to propagate directly into the ventricular contractile cells from the atria. If it did, the ventricles would contract from the top down: = must stop the ap because want the ventricles to contract from the bottom up.
