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Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart .
These hormones (i.e., catecholamines and corticosteroids) affect a variety of organs like skeletal muscles along with the muscles surrounding certain bodily systems such as the cardiovascular system and respiratory system, causing an increase in force production by the skeletal muscles along with accelerated heart rate and breathing rate.
Cardiac muscle cells are joined to neighboring cells by intercalated discs, and when joined in a visible unit they are described as a cardiac muscle fiber. [8] Smooth muscle cells control involuntary movements such as the peristalsis contractions in the esophagus and stomach. Smooth muscle has no myofibrils or sarcomeres and is therefore non ...
T-tubules (transverse tubules) are extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells.With membranes that contain large concentrations of ion channels, transporters, and pumps, T-tubules permit rapid transmission of the action potential into the cell, and also play an important role in regulating cellular calcium concentration.
The bundle of His (BH) [1]: 58 or His bundle (HB) [1]: 232 (/ h ɪ s / "hiss" [2]) is a collection of heart muscle cells specialized for electrical conduction.As part of the electrical conduction system of the heart, it transmits the electrical impulses from the atrioventricular node (located between the atria and the ventricles) to the point of the apex of the fascicular branches via the ...
The heart is a functional syncytium as opposed to a skeletal muscle syncytium. In a functional syncytium, electrical impulses propagate freely between cells in every direction, so that the myocardium functions as a single contractile unit. This property allows rapid, synchronous depolarization of the myocardium.
The force of each contraction of the heart muscle is proportional to the preload, described as the Frank-Starling mechanism. This states that the force of contraction is directly proportional to the initial length of muscle fiber, meaning a ventricle will contract more forcefully, the more it is stretched. [8] [40]
The myocytes of the heart (also called the myocardial fibers) are arranged in a general circumferential direction in the ventricles. In the left ventricle (LV), the fiber will change gradually in direction from a certain longitudinal-circumferential direction in the outer layer of the heart (epicardium) to another angulated direction almost orthogonal in the inner wall (endocardium), becoming ...