The heart muscle provides the vital activity of all tissues, cells and organs. The transport of substances in the body is due to the constant circulation of blood; it also provides the maintenance of homeostasis.
The 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 arterial blood, and the right half - 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 that have atrioventricular valves: bicuspid (left half of the heart) and tricuspid (right half of the heart). These valves during heart contraction prevent the return of blood in the atrium. At the exit of the aorta and pulmonary artery, half-month valves are placed 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 muscle. Muscle fiber consists of myofibrils, sarcoplasm and sarcolemma.
Thanks to the heart, blood is circulated through the blood vessels. The rhythmic contraction of the muscles of the atria and ventricles (systole) alternates with its relaxation (diastole). The successive change of systole and diastole makes up the cycle of the 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
Myocardial excitability is its ability to respond to electrical, mechanical, thermal and chemical stimuli. Excitation and contraction of the heart muscle occurs when the stimulus reaches a threshold force. Irritations weaker than the threshold are not effective, and superthresholds 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 shortens with increasing frequency and lengthens with a slowdown in heart contractions.
Excited heart muscle for a short time loses the ability to respond to additional stimulation or impulses coming from the focus of automation. Such excitability is called refractoriness. Strong irritants that act on the muscle during a period of relative refractoriness cause an extraordinary contraction of the heart - the so-called extrasystole.
Myocardial contractility has features in comparison with skeletal muscle tissue. Excitation and contraction in the heart muscle last longer than in the skeletal muscle. In the heart muscle, aerobic processes of resynthesis of macroergic compounds predominate . During diastole, an automatic change in the membrane potential occurs simultaneously in several cells in different parts of the node. From here, the excitation spreads through the muscles of the atria and reaches the atrioventricular node, which is considered the center of automation of the second order. If you turn off the sinoatrial node (by applying a ligature, cooling, poisons), then after a while the ventricles begin to contract in a more rare rhythm under the influence of impulses arising in the atrioventricular node.
Carrying out excitement in different parts of the heart is not the same. It should be said that in warm-blooded animals the rate of conduction of excitation along the muscle fibers of the atria is about 1.0 m / s; in the conduction system of the ventricles up to 4.2 m / s; in the myocardium of the ventricles up to 0.9 m / s.
A characteristic feature of the excitation in the heart muscle is that the action potential that arose in one area of muscle tissue extends to neighboring areas.