So now we're going to discuss the cardiac conduction system and its components.
This is a deeper dive into the biomechanical and electromechanical actions of this incredible
organ called the heart.
So now let’s take a closer look at the heart and how it functions as a circulatory muscle.
You see, the myocardium is a muscle unlike any other muscle within the human body.
It’s unique in that it can generate it’s own electrical impulse known as automaticity.
A special part of the heart located in the superior aspect of the right atrium called
the Sinoatrial node or the SA node for short, works like an internal dynamic pacemaker.
This internal pacemaker, when the heart is working correctly, generates an electrical
impulse that then travels through the myocardium in a very organized and deliberate fashion.
You see, this SA node generates an electrical impulse at about a rate of 60-100 times per
minute.
Now let’s follow the pathway of the electrical impulse from the SA node to where it terminates
at the end of the purkinje fibres.
So after the SA node initiates an electrical impulse, that impulse travels via the pathways
called the internodal pathways.
These travel throughout the right and the left atria and then depolarizes the myocardial
cells which causes the actual muscle in the atrium to contract.
From the atria, the electrical impulse travels along the pathway to the atrioventricular
(or AV) node where it may be delayed strategically before it moves through the bundle of His
and ultimately into the purkinje fibres which travel down, through and wraps around the
ventricles completing the electromechanical cycle of a complete heart beat.
See, the delay in the AV node, which is located in the left lower wall of the right atrium,
is a necessary process in order to allow the ventricles to beat independently of each other,
and thereby they operate as a double pump action.
If for whatever reason the SA node does not operate properly as the primary impulse generator
or pacemaker, the AV node then can begin sending an electrical impulse instead.
Though the AV node can generate its own impulse, it does so at a slower pace which ranges between
40 and 60 impulses per minute.
The impulse generated from the AV node then travels through the bundle of His which is
the route that the impulse travels to reach the purkinje fibres which wrap around those
ventricles we talked about earlier.
This ventricle contraction then circulates the majority of the oxygenated blood throughout
the body.
The bundle of His is the route of electrical transmission which travels between the atria
and the ventricles.
Now after the impulse reaches the bundle of His, it travels down the length of the interventricular
septum and leads to the left and right bundle branches, of which the left bundle branch
has two fascicles because the left ventricle is larger than the right ventricle.
These bundle branches terminate into the Purkinje fibres which depolarize the ventricular cells,
and cause the ventricular muscles to contract.
In the case that both the SA and the AV nodes do not generate electrical impulses properly,
the Purkinje fibres, which are located within the ventricles, then become the primary pacemaker
source which only generates electrical impulses in the range of around 15-40 beats per minute.
Usually this is too slow to produce adequate systolic blood pressure or oxygenation of
cells within the body.