conducting system of human heart.

conducting system of human heart-Short note:

Short note on the conducting system of human heart.

Introduction to the conducting system of human heart:

The heart present in the human body has a specialized conductive system through which impulses from the Sinoatrial node are transmitted to all other parts of the heart.

Conductive system of the human heart:

Modified cardiac muscle fibres from the conducting system of human heart. This cardiac muscle fibers has fewer striations and indistinct boundaries.

This system is composed of SA(Sinoatrial)node, Interatrial tract, Internodal conduction pathway,AV(Atrioventricular)node,AV(Atrioventricular) bundle of His, Purkinje fibres.

Electrical conduction system of the heart,Image by-Madhero88, Source,License-CC BY-SA 3.0

1.Sinoatrial node(SA node):

  The sinus node also known as sinoatrial node is a small, flattened, ellipsoid strip of specialized cardiac muscle,about 3mm wide and the length of the SA(Sinoatrial) node is about 15mm,and thickness of it is about 1mm .

The SA(Sinoatrial) node is situated in the superior posterolateral wall of the right atrium immediately below and sightly lateral to the opening of the superior vena cavae.

The fibres of this node have almost no contractile muscle filaments.

From the SA(Sinoatrial) node of the human heart, spontaneous rhythmical electrical impulses arise and  spread in all directions to cardiac muscles of atria , Interatrial tract to left atrium and Internodal tracts to AV(Atrioventricular) node .

The SA(Sinoatrial) node has the highest inherent rate of depolarization and is known as the pacemaker of the heart.

2.Interatrial tract (Bachman's Bundle) : 

Bachman's bundle or interatrial tract is a band of spealized muscle fibres that run from the SA node(right atrium) to the left atrium.

Bachman's bundle causes simultaneous depolarization of the atria since the velocity of conduction of impulses in this tract is faster than the rest of the atrial muscles.

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3.Internodal conduction pathway:

Impulses from the SA(Sinoatrial) node are conducted to the AV(Atrioventricular) node more more rapidly than they can travel by passing along the ordinary myocardium.

Some specialized fibres called internodal fibres are involves in this conduction and they are known as internodal fibers. These are ,

   A.Anterior internodal fibers of Bachman:

   The anterior internodal fibers of Bachman leaves the anterior end of SA(Sinoatrial) node and passes anterior to the superior vena cava opening.

It then descends on the atrial septum and ends in the AV(Atrioventricular) node .

  B.Middle internodal fibers of Wenckebach:

 Middle internodal fibers of Wenckebach leaves the posterior end of the SA node and passes posterior to superior vena cava opening.

It then descends on the atrial septum to end in the AV node.

  C.Posterior internodal fibers of Thorel :

 These fibers leaves the posterior part of the SA(Sinoatrial) node and descends through the crista terminalis and the valve of inferior vena cava to the AV(Sinoatrial) node .

Cardiac Conduction System,Image by-Cypressvine,Source, License-CC BY-SA4.0

4. Atrioventricular node(AV node):

The atrioventricular node(AV) is a second clump of specialized myocardial conductive cells ,located in the inferior portion of the right atrium within the atrioventricular septum .

AV(Atrioventricular) node is stimulated by the excitation wave that travels through internodal tracts and atrial myocardium. The AV(Atrioventricular) bundle then conducts the cardiac impulses from here to the ventricles.

5.AV Bundle of His:

The AV bundle arises from the AV(Atrioventricular) node and proceeds through the interventricular septum before dividing into two atrioventricular bundle branches, commonly known as the right and the left bundle branches.

The left bundle branches has two fascicles. The left bundle branch supplies the left ventricle and the right bundle branch supplies the right ventricle.

Considerably left ventricle is much larger than the right ventricle , therefore left bundle branch is also larger than the right bundle branch.

Both bundle branches descend and reach the apex of the heart where they connect with the Purkinje fibers .

6. Purkinje fibers:

 These are the additional myocardial conductive fibers . Purkinje fibers spread the impulse to the myocardial contractile cells in the ventricles.

They extend throughout the myocardium from the apex of the heart towards the atrioventricular septum and the base of the heart.

These fibers have a first inherent conduction rate and the electrical impulse reaches all of the ventricular muscle cells in about 75ms.  The Purkinje fibers also have very few myofibrils.

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