This tissue is the main constituent of the heart wall. Although he is striated, his control is involuntary (It is innervated by the two branches of the autonomic nervous system - the sympathetic and the parasympathetic).
The heart muscle fibers are quadrangular and have one or two nuclei located in the center of the fiber. Already skeletal muscle cells contain several nuclei distributed around the periphery of the cell.
The heart fibers are interconnected with each other. These fibers are arranged in parallel, and physically connected by junctions that allow the conduction of a stimulus from one fiber to another. Between the fibers, there is the interposition of a interleaved disc, which is nothing more than the thickening of the cell membrane. This disc is characteristic of cardiac muscle tissue. Its function is to increase muscle strength and to facilitate the conduction of impulse from one fiber to another. When one tissue fiber is stimulated, all the others will be stimulated.
Normal cardiac muscle tissue contracts and relaxes rapidly, continuously and rhythmically at about 75 times per minute. For this work, the demand for oxygen is much higher than that of skeletal muscle tissue. Mitochondria are also larger and in large numbers when compared to those of skeletal muscles.
Smooth muscle tissue
Smooth muscle cells are involuntary, non-striated and smaller than skeletal striated fibers. They feature a single central core. Its actin and myosin filaments are scattered in the cytoplasm, without the arrangement seen for skeletal muscle cells. Muscle contraction is similar to the one previously seen.
Smooth muscle is controlled by the nerves of the autonomic nervous system (sympathetic and parasympathetic). Smooth muscle is present, for example, in the wall of digestive organs, blood vessels, urinary bladder and uterus. Smooth muscle tissue can also be stimulated to function by distending the organ wall.
Muscle Action Groups
Skeletal muscle is a cluster of muscle cells (fibers) encased in delicate nervous tissue. As a skeletal muscle approaches its insertion, the mass formed by contractile elements, called the womb, abruptly ends and is continued by connective tissue fibers known as insertion tendons. Flat tendons are called aponeuroses. The collagen fibers of the tendon bind with those of the periosteum and the bone itself, joining the skeletal and muscular bone systems.
Most movements are coordinated by various skeletal muscles acting in groups. Depending on the type of movement, there are different muscle groups on either side of a joint. Thus, in a joint, the flexor muscles are opposite the extensors, the adductors as opposed to the abductors etc.
The muscle that causes the desired action is called the agonist. At the same time, the group that opposes the agonist is called the antagonist. Thus, if the agonist group contracts, the antagonist relaxes and allows the desired movement.
In addition to agonists and antagonists, there are synergists. These muscles serve to steady, smooth movement, prevent unwanted movement and promote efficient agonist action. The last group is the fasteners. Its function is to stabilize the origin of agonist movements so that they are performed efficiently.