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Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in : skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives the ability to contract. Muscle tissue contains special contractile proteins called actin and myosin which interact to cause movement. Among many other muscle proteins, present are two regulatory proteins, troponin and tropomyosin. Muscle is formed during embryonic development, in a process known as myogenesis.
Skeletal muscle tissue is striated consisting of elongated, multinucleate called , and is responsible for movements of the body. Other tissues in skeletal muscle include and perimysium. Smooth and cardiac muscle contract involuntarily, without conscious intervention. These muscle types may be activated both through the interaction of the central nervous system as well as by innervation from peripheral nerve plexus or endocrine system (hormonal) activation. Skeletal muscle only contracts voluntarily, under the influence of the central nervous system. are a form of non-conscious activation of skeletal muscles, but nonetheless arise through activation of the central nervous system, albeit not engaging cerebral cortex structures until after the contraction has occurred.
The different muscle types vary in their response to and such as acetylcholine, noradrenaline, adrenaline, and nitric oxide which depends on muscle type and the exact location of the muscle.
Sub-categorization of muscle tissue is also possible, depending on among other things the content of myoglobin, mitochondria, and myosin ATPase etc.
The same phenomenon occurred in Greek language, in which μῦς, mȳs, means both "mouse" and "muscle".
There are three types of muscle tissue in that are based on their pattern of striation: transversely striated, obliquely striated, and smooth muscle. In arthropods there is no smooth muscle. The transversely striated type is the most similar to the skeletal muscle in vertebrates.
Vertebrate skeletal muscle tissue is an elongated, striated muscle tissue, with the fibres ranging from 3-8 micrometers in width and from 18 to 200 micrometers in breadth. In the uterine wall, during pregnancy, they enlarge in length from 70 to 500 micrometers. Skeletal striated muscle tissue is arranged in regular, parallel bundles of , which contain many contractile units known as , which give the tissue its striated (striped) appearance. Skeletal muscle is voluntary muscle, anchored by or sometimes by aponeurosis to , and is used to effect skeleton movement such as locomotion and to Proprioception. Postural control is generally maintained as an unconscious reflex, but the responsible muscles can also react to conscious control. The body mass of an average adult man is made up of 42% of skeletal muscle, and an average adult woman is made up of 36%.
Cardiac muscle tissue is found only in the walls of the heart as myocardium, and it is an involuntary muscle controlled by the autonomic nervous system. Cardiac muscle tissue is striated like skeletal muscle, containing sarcomeres in highly regular arrangements of bundles. While skeletal muscles are arranged in regular, parallel bundles, cardiac muscle connects at branching, irregular angles known as intercalated discs.
Smooth muscle tissue is non-striated and involuntary. Smooth muscle is found within the walls of organs and structures such as the esophagus, stomach, , bronchus, uterus, urethra, Urinary bladder, , and the arrector pili in the skin that control the erection of body hair.
| smooth muscle | cardiac muscle | skeletal muscle | |
| Anatomy | |||
| Neuromuscular junction | none | present | |
| Fibers | fusiform, short (<0.4 mm) | branching | cylindrical, long (<15 cm) |
| Mitochondrion | numerous | many to few (by type) | |
| Cell nucleus | 1 | 1 | >1 |
| none | present, max. length 2.6 μm | present, max. length 3.7 μm | |
| Syncytium | none (independent cells) | none (but functional as such) | present |
| Sarcoplasmic reticulum | little elaborated | moderately elaborated | highly elaborated |
| ATPase | little | moderate | abundant |
| Physiology | |||
| Self-regulation | spontaneous action (slow) | yes (rapid) | none (requires nerve stimulus) |
| Response to stimulus | unresponsive | "all-or-nothing" | "all-or-nothing" |
| Action potential | yes | yes | yes |
| Workspace | Force/length curve is variable | the increase in the force/length curve | at the peak of the force/length curve |
| Response to stimulus |
The density of mammalian skeletal muscle tissue is about 1.06 kg/liter. This can be contrasted with the density of adipose tissue (fat), which is 0.9196 kg/liter. This makes muscle tissue approximately 15% denser than fat tissue.
Skeletal muscle is a highly oxygen-consuming tissue, and oxidative DNA damage that is induced by reactive oxygen species tends to accumulate with age. The oxidative DNA damage 8-OHdG accumulates in heart and skeletal muscle of both mouse and rat with age. Also, DNA double-strand breaks accumulate with age in the skeletal muscle of mice.
Smooth muscle is found within the walls of blood vessels (such smooth muscle specifically being termed vascular smooth muscle) such as in the tunica media layer of the large (aorta) and small arteries, arterioles and veins. Smooth muscle is also found in lymphatic vessels, the urinary bladder, uterus (termed uterine smooth muscle), male and female reproductive tracts, the gastrointestinal tract, the respiratory tract, the arrector pili of skin, the ciliary muscle, and the iris of the eye. The structure and function is basically the same in smooth muscle cells in different organs, but the inducing stimuli differ substantially, in order to perform individual actions in the body at individual times. In addition, the glomeruli of the kidneys contain smooth muscle-like cells called .
Coordinated contractions of cardiac muscle cells in the heart propel blood out of the atria and ventricles to the blood vessels of the left/body/systemic and right/lungs/pulmonary circulatory systems. This complex mechanism illustrates systole of the heart.
Cardiac muscle cells, unlike most other tissues in the body, rely on an available blood and electrical supply to deliver oxygen and nutrients and to remove waste products such as carbon dioxide. The coronary arteries help fulfill this function.
During development, (muscle progenitor cells) either remain in the somite to form muscles associated with the vertebral column or migrate out into the body to form all other muscles. Myoblast migration is preceded by the formation of connective tissue frameworks, usually formed from the somatic lateral plate mesoderm. Myoblasts follow chemical signals to the appropriate locations, where they fuse into elongate skeletal muscle cells.
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