Heart muscle - anatomical and physiological features

The heart muscle ensures the vital activity of all tissues, cells and organs. Transport of substances in the body is due to the constant circulation of blood; It also ensures the maintenance of homeostasis.

Structure of the heart muscle

The heart is represented by two halves - left and right, each of which consists of the atrium and ventricle. The left half of the heart pumps blood, and the right side - venous. Therefore, the heart muscle of the left half is much thicker than the right. The muscles of the atria and ventricles are separated by fibrous rings, which have atrioventricular valves: bicuspid (left half of the heart) and tricuspid (right half of the heart). These valves during the reduction of the heart prevent the return of blood to the atria. The aorta and pulmonary arteries are placed half-monthly valves that prevent the return of blood to the ventricles during a common diastole of the heart.

The heart muscle belongs to the striated muscle tissue. Therefore, this muscle tissue has the same properties as skeletal muscles. The muscle fiber consists of myofibrils, sarcoplasm and sarcolemma.

Thanks to the heart, the circulation of blood through the blood vessels is ensured. Rhythmic contraction of the muscles of the atria and ventricles (systole) alternates with its relaxation (diastole). Consecutive change of systole and diastole makes a cycle of work of heart. The heart muscle works rhythmically, which is provided by a system that conducts excitation in different parts of the heart

Physiological properties of the heart muscle

The excitability of the myocardium is the ability of it to respond to the actions of electrical, mechanical, thermal and chemical stimuli. Excitation and contraction of the heart muscle occurs when the stimulus reaches the threshold force. Irritations weaker than the threshold are not effective, and suprathreshold ones do not change the strength of myocardial contraction.

Excitation of the muscle tissue of the heart is accompanied by the appearance of an action potential. It is shortened by acceleration and lengthens with a slowing of the contractions of the heart.

The excited cardiac muscle for a short time loses its ability to respond to additional stimuli or impulses coming from the hearth of the automatic system. Such non-excitability is called refractoriness. Strong stimuli, which act on the muscle during the period of relative refractoriness, cause an extraordinary shortening of the heart - the so-called extrasystole.

The contractility of the myocardium has features in comparison with skeletal muscle tissue. Excitation and contraction in the cardiac muscle last longer than in the skeletal muscle. The cardiac muscle is dominated by aerobic processes of resynthesis of macroergic compounds. During diastole, the membrane potential is automatically changed simultaneously in several cells in different parts of the node. Hence the excitation spreads through the muscles of the atria and reaches the atrioventricular node, which is considered to be the center of the second order automaticity. If you turn off the sinoatrial node (ligation, cooling, poisons), after a while the ventricles will begin to contract in a more rare rhythm under the influence of impulses that appear in the atrioventricular node.

The excitation in different parts of the heart is not the same. It should be noted that in warm-blooded animals the rate of excitation of the muscle fibers of the atria is about 1.0 m / s; In the ventricular system up to 4.2 m / s; In the myocardium of the ventricles to 0.9 m / s.

A characteristic feature of the excitation in the heart muscle is that the action potential that has arisen in one area of the muscle tissue extends to neighboring sites.