Control of Heart Rate|Heart Conduction.
The electric conduction system of the heart is an intrinsic process in the heart which generates electric impulses enabling the heart to contract (systole) and relax (diastole) rhythmically. It is this efficient and synchronized generation of heart electricity which controls the heart rate and which is responsible for the time ordered and rhythmic cardiac cycle and enables the heart to pump blood to all parts of the body (systemic circulation) and the lungs (pulmonary circulation). This electrical activity of the heart is measured with the help of the electrocardiogram (ECG).
Cardiac Conduction System.
The cardiac or heart conduction system consists of specialized heart muscle cells and conducting fibers which generate and conduct electric impulses through the heart. This system is made up of :
- Cardiac pacemaker which is the Sinoatrial Node (SAN) which generates electric impulses.
- The AV Node which acts as a junction box (of sorts) and also generates electric impulses on its own but at a slower rate.
- The Bundle of His which acts as a cable for transfer of the electric impulse.
- The Right Bundle Branch and the Left Bundle Branch which transmit the impulse to the purkinje fibers which further conduct this impulse throughout the ventricular myocardium.
What Makes The Heart Beat.
The electric impulse generated by the SA node spreads across both the atria and then travels to the ventricles. It is this electric impulse which makes the heart beat on its own in a rhythmic and synchronous manner (intrinsic automaticity), with the atria contracting first followed then by the ventricles. Depolarization is the word used to describe contraction of the heart chambers and repolarization is used to describe relaxation.
The electric impulse generated in the sinoatrial node in the left atrium travels to the right atrium via the bachmann’s bundle and then both the atria contract. At the same time, the impulse travels from the SA node to the atrioventricular node via the internodal pathways.
From the AV node, after a short delay, the impulse has to travel to ventricular myocardium to make the ventricles contract. It does so by traveling through the bundle of His to the left and right bundle branches and then to the Purkinje fibers and to the endocardium situated at the apex of the heart, from where it enters the ventricular myocardium.
Image of heart conduction system which controls the heart.
Click on image to enlarge.
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