the

Conduction system of the heart - Sinoatrial node, AV Node, Bundle of His, Purkinje fibers Animation

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conducting system of the heart

components the conducting system of the

heart is made up of specialized cardiac

muscle fibers and is responsible for

initiation and conduction of cardiac

impulse the conducting system of the

heart consists of the following five

components sinoatrial node atrial

ventricular node atrioventricular bundle

right and left branches of bundle of his

sub endocardial Purkinje fibers

sinoatrial node sinoatrial node is also

known as node of Keith black it is a

small horseshoe shaped mass having

specialized myocardial fibers situated

in the wall of the right atrium in the

upper part of sulcus terminalis just

below the opening of the superior vena

cava it is known as pacemaker of the

heart because it generates impulses

about 70 per minute and initiates the

contraction of cardiac muscle producing

a heartbeat atrial ventricular node is

also known as node of taurah it is

smaller than the SA node and is located

in the lower part of the atrial septum

just above the attachment of septal

cusps of the tricuspid valve or opening

of the coronary sinus it conducts the

cardiac impulse to the ventricle by the

atrioventricular bundle the AV node is

capable of generating impulses at a rate

of about 60 per minute the speed of

conduction of cardiac impulse which is

about 0.11 seconds provides sufficient

time to the atria to empty their blood

into the ventricle before ventricles

start contracting atrial ventricular

bundle it begins from the AV node

crosses the AV ring and runs along the

inferior part of the membranous part of

the interventricular septum where it

divides into the left and right branches

since the skeleton which is a fibrous

framework of the heart separates the

muscles of atria from the muscles of the

ventricles the bun

of his is the only means of conducting

impulses from the atria to the

ventricles right and left branches of

the bundle of his the right branch

passes down to the right side of the

interventricular septum and then becomes

sub endocardial on the right side of the

septum a large part of it continues in

the septum marginal true baculum to

reach the anterior papillary muscle and

anterior wall of the ventricle its

Purkinje fibers then spread out beneath

the endocardium the left branch descends

on the left side of the ventricular

septum divides into Purkinje fibers

which are distributed to the septum and

left ventricle Purkinje fibers they are

the terminal branches of the right and

left branches of the bundle of His and

spread sub endocardial II over the

septum and the rest of the ventricular

wall the conducting system and mode of

contraction of cardiac muscle is

summarized as follows the SA node a

spontaneous source of cardiac impulse

initiates an impulse which rapidly

spreads to the muscles of the atria

making them contract the AV node picks

up the cardiac impulse from atria and

conducts it through the atrioventricular

bundle and its branches to the papillary

muscles and the walls of the ventricles

the papillary muscles contract first to

tighten the chordae tendineae

and then the contraction of the

ventricular muscle occurs arterial

supply of the conducting system the hole

of the conducting system of the heart is

supplied by the right coronary artery

except a part of the left branch of the

AV bundle which is supplied by the left

coronary artery clinical correlation

conducting system defects the defect or

damage of conducting system causes

cardiac arrhythmias the SA node is the

spontaneous source of generation of

cardiac impulses the AV node picks up

these impulses from atria and sends them

to the ventricles through AV bundle the

only means through which impulses can

spread from the atria two ventricles

if the AV bundle fails to conduct normal

impulses

there is alteration and the rhythmic

contraction of the ventricle which is

known as irate Mia's if complete bundle

block occurs there is complete

dissociation in the rate of contraction

of atria and ventricles the commonest

cause of defective conduction through AV

bundle is a thorough sclerosis of

coronary arteries which leads to

diminished blood supply to the

conducting system an important point to

be noted here is that rapid pulse is

called tachycardia the slow pulse is

called bradycardia whereas a regular

pulse is called a wreath Mia