CONDUCTING SYSTEM OF THE HEART

Hello friends.. So far we are discussing about the " THE CARDIOVASCULAR SYSTEM" .In today's topic we are going to discuss about the " CONDUCTING SYSTEM OF THE HEART". If you have any doubts kindly post in the comment section below. I'm giving the link of my YouTube channel where you can get these content videos in both English and Tamil.
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INTRODUCTION:

The heart is having the property of auto rhythmicity .It means the heart generates its own electrical impulses and beats independently of nervous or hormonal control, i.e. it is not dependant on external mechanisms to initiate each heartbeat.

It is supplied with both sympathetic and parasympathetic nerve fibers, which increase and decrease respectively the intrinsic heart rate [the heart beat when all the cardiac neural and and hormonal inputs are removed].The heart responds to a number of circulating hormones, which includes adrenaline (epinephrine) and thyroxine.

DIFFERENCE BETWEEN DEPOLARIZATION AND REPOLARIZATION

SINOATRIAL NODE :

The SA node is a specialized cells which lies in the wall of the right atrium near the opening of the superior vena cava. The sinoatrial cells generate regular impulses .They discharge electrical impulses (depolarization) regularly, which is between 60 to 80 times a minute.

This depolarization is followed by the recovery (repolarization), but immediately their instability leads them to discharge again, setting the heart rate. SA node is called the pacemaker of the heart because the SA node discharges faster than any other part of the heart, it normally sets the heart rate. The rapid firing of the SA node triggers atrial contraction.

ATRIOVENTRICULAR NODE:

In the wall of the atrial septum AV node is situated which is a small mass of neuromuscular tissue. The AV node transmits the electrical signals from the atria into the ventricles merely. There is a delay when the AV node passes electrical signals ; the electrical signal takes 0.1 second to pass through into the ventricles.

This delay allows the atria to finish contracting before the ventricles start contraction. The AV node is a secondary pacemaker when there is a problem with the SA node or when there is a problem in the transmission of impulses from the atria. The intrinsic firing rate of AV node is slower than that of the SA node

AV node 40–60 firing rate per minute.

SA node 60-80 firing rate per minute .

ATRIOVENTRICULAR BUNDLE OR BUNDLE OF HIS

The Bundle of His is a mass of specialized fibers which originates from the AV node. The AV bundle crosses the fibrous ring which separates the atria and the ventricles , and then crosses at the upper end of the ventricular septum and it divides into right and left bundle branches. The branches break up into fine fibers, called the Purkinje fibers.

The electrical impulses from the AV node is transmitted to the AV bundle, bundle branches and Purkinje fibers to the apex of the myocardium from which the wave of ventricular contraction begins, then moves upwards and outwards , which pumps blood into the pulmonary artery and the aorta.

NERVE SUPPLY TO THE HEART:

The heart is having an influence by the autonomic nerves (sympathetic and parasympathetic) which originates in the cardiovascular center in the medulla oblongata. The Vagus nerve which is a parasympathetic nerve supplies mainly the SA and AV nodes and atrial muscle. Vagal stimulation reduces the rate , force of the heartbeat and the rate at which impulses are produced.

Sympathetic nerves supply the myocardium of atria and ventricles ,the SA and AV nodes and the stimulation of the sympathetic nerves increases the rate and force of the heartbeat.