In order to ensure a constant flow of blood through the body, our heart must continuously contract. This process is controlled by the conducting system of the heart.
The conducting system is a group of atypical cardiocytes. Those heart cells differ from others in their structure and function. Atypical cardiomyocytes generate and conduct electrical impulses, causing normal working cardiomyocytes to contract.
Let’s consider the structure of the conducting system. It consists of the following structures:
The sinus (sinuatrial) node (nodus sinuatrialis). It is located in the superior part of the right atrium. This structure has automatism, it is able to excite itself and pass impulses to the atria.
The atrial internodular bundles
1. The bachmann’s bundle
2. The torel’s bundle
3. The wenckebach’s bundle
They are localized in the atrial myocardium. They transmit excitation from the sinuatrial node to the next, atrioventricular node.
The atrioventricular node (Aschoff-Tawara node) (nodus atrioventricularis) is located in the posteroinferior part of the right atrium and in the interatrial septum. It somewhat delays the conduction of the impulse from the atria to the ventricles.
The atrioventricular bundle (bundle of His) (fasciculus atrioventricularis) is located in the superior part of the interventricular septum. Then it divides into two cruses.
The right crus of the bundle of His (crus dextrum)
The left crus of the bundle of His (crus sinistrum)
They pass along both sides of the interventricular septum and pass excitation to the ventricles.
Eventually, the cruses branch into small subendocardial fibers, which are called Purkinje fibers. They provide stimulation of the ventricular myocardium.
All these structures are interconnected and receive the very first impulse from the so-called pacemaker. In most cases, the sinuatrial node is normally the pacemaker.
However, in various diseases, impulses can occur in other parts of the conducting system, such pacemakers are called ectopic.
Impulses provide rhythmic work of the heart, with a sequential contraction of the atria and ventricles, which in general makes up the cardiac cycle.
It consists of the following phases:
The atrial diastole is the relaxation of the walls of the atria when blood enters both the atria and the ventricles.
The atrial systole passes during their contraction and blood is additionally ejected into the ventricles.
In the ventricular diastole, their walls relax, and the cavities are filled with blood.
The ventricular systole is the ejection of blood from the ventricles into the aorta and pulmonary artery.
Normally, the heart makes 60-80 contractions per minute. However, the heartbeat rate may be slow or accelerated. This condition is called arrhythmia.
Conducting system of the heart
- Sinus (sinuatrial) node
- nodus sinuatrialis
- Atrial internodular bundles and interatrial bundle
- fasciculi atriali internodii et fasciculus interatrialis
- Atrioventricular node
- nodus atrioventricularis
- Right and left cruses of the bundle of His
- crus dextrum et sinistrum
- Subendocardial branches
- rr. subendocardiales
- Cardiac cycle
- cordis cursus