MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Y.I. Fedoniuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

SECTION 5. BLOOD AND LYMPH CIRCULATION. PATHOPHYSIOLOGY

CARDIAC ACTIVITY

6. MAIN PROPERTIES OF THE CARDIAC MUSCLE

6.2. CONDUCTIVITY. THE Conduction system of The Heart

Between the cardiomyocytes lies a network of Cells and processes responsible for generating excitation and conducting it to the cardiomyocytes. This constitutes the conduction System of the heart. It is composed of specialized atypical Muscle tissue that is relatively poor in myofibrils, rich in sarcoplasm, and structurally resembles embryonic muscle tissue (Fig. 5.10).

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Fig. 5.10. Diagram of the conduction system

The cardiac conduction system consists of the sinus node, atrioventricular node, sinoatrial and atrioventricular (His bundle) tracts, and Purkinje fibers.

The sinus node is located in the right atrium between the openings of the superior and inferior venae cavae. This node is referred to as the pacemaker because it is the primary site where cardiac excitation spontaneously originates, driving heart contractions at an average rate of 60–70 beats per minute. The excitation spreads from the sinus node to the left atrium and the atrioventricular node.

The atrioventricular node (Aschoff-Tawara node) is situated within the interatrial septum near the junction of the atria and ventricles. The atrioventricular bundle (bundle of His) originates from this node, passes through the atrioventricular septum, and divides into right and left branches running along the interventricular septum. Near the apex of the heart, the Branches of the bundle of His curve upward and transition into Purkinje fibers, which ramify throughout the working myocardium of the ventricles.

Every component of the conduction system exhibits automaticity. Furthermore, there is an automaticity gradient: the capacity for automaticity decreases progressively in the Regions of the conduction system located farther from the sinus node.