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The cardiac cycle’s run by cardiac muscle cells, namely,
Myocardial conducting cells send signals electricly!
Nodal tissues make action potentials through selfexcitation!
Conduction fibers send these to other cells to start their action!

The heart’s physiological pacemaker, the SA node, see!
Its impulses are conducted to cardiomyocytes! Wee!
Cardiomyocyte intercalated discs have gap junctions,
Which gives ionic continuity for synchronized contractions!

Under a fat pad, the SA node in the right atrium hides!
In the subepicardiac layer the SA node resides!
It features cardiac pacemaker cells, with transition cells on its sides!

P cells contain cholinergic and adrenergic receptors,
Which respond to autonomic ganglion neurotransmitters!
Through the right atrium internodal conduction pathways go!
These three branches connect SA node and AV node so you know!

These conduction pathways transmit action potentials rapidly,
So they can go from the SA node to the AV node quickly!

The AV node is the secondary pacemaker of the heart!
This smaller node of the interatrial septum is a part!
It’s in the subendocardiac layer in Koch’s triangle!
Conducts electrical signals from SA node to ventricle!

The AV node’s the one path to ventricles! APs cross it must!
Since atrioventricular septum cartilage can’t conduct!
Autonomic ganglion cells surround the AV node but they,
Don’t synapse with the AV node, unlike the SA node, okay?

The AV node has less P cells but more transition cells! Got it?
It passes through the fibrous cardiac skeleton and this bit,
Is the start of the AV bundle, known as the bundle of His! That’s lit!

The bundle of His goes through the fibrous trigone and into the,
Membranous part of the interventricular septum, oh yeah!
Importantly it only lets action potentials go forward!
No retrograde transmission can occur, it only goes forward!

From membranous to muscular interventricular septum,
Bundle bifurcates now left and right bundle branches it becomes!

The left at muscular interventricular septum starts! Next,
It trifurcates to these divisions on approach to the apex!
Posterior, septal, anterior go to papillary muscles,
Interventricular septum and also left ventricle walls!

The right branch past membranous interventricular septum runs!
Remember to the right of the interventricular septum!
It branches to ventricular walls then to the apex proceeds,
Through septomarginal band then to papillary muscles leads!

The left and right bundles have subendocardiac branches and,
These Purkinje fibers are found along their full length, understand?
These go to the apex, then up and back through the ventricle walls extend!

Purkinje fibers have many gap junctions for fast signaling!
Thus more ions pass from one cell to the next for faster conducting!
Faster than ventricular muscles and AV nodal fibers!
And there’s little to no contraction due to few myofibrils!

Fast bundle transmission through the ventricles makes up for delay,
So ventricles contract shortly after the atria hurray!

The main branches of the AV bundle are insulated so,
Early excitation of nearby cardiac tissue’s blocked, yo!
Depolarization starts with papillary muscle then goes,
To the ventricle apex, and finally to the walls it flows!

Know the ANS has an effect on cardiac conduction!
Cardiac plexus tissue gives sympathetic stimulation!
Parasympathetic influence comes from cranial nerve X!
There’s less excitability at SA and AV nodes then!

The sympathetic nervous system gets epinephrine released,
To bind receptors in SA and AV nodes, causing increased,
SA node depolarization rate, so now the heart rate gets increased!

Cardiomyocytes receive sympathetic signals also!
They increase inotropy and now cardiac output will grow!
Parasympathetic activation at SA and AV,
Nodes results in reduced cardiac input and know this is key!

It slows SA node activation, dampens contractility,
Of cardiomyocytes! Reduced cardiac output we see!