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  • 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.

So now we're going to discuss the cardiac conduction system and its components.

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B2 中高級 美國腔

心臟傳導系統 (The Cardiac Conduction System)

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    alex 發佈於 2021 年 01 月 14 日
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