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There are three kinds of muscle tissue in the body: skeletal (or voluntary), smooth (or involuntary) and cardiac.
– Skeletal muscle: this type of muscle moves and supports the skeleton, hence its name. In addition, they shape the body and help it perform day-to-day movements. They are also called voluntary because the nervous system has to make a conscious decision in order to activate contraction in any of these muscles and move the body.
Skeletal muscle is also called striated muscle, because it is composed of fibers arranged in parallel stripes or horizontal striae.
Although muscle cells have the same components as a regular cell, there are two differences: they have a higher number of myofibrils and mitochondria (where cellular respiration takes place), because they have to deliver a greater amount of energy to the muscle.
They take up most of the muscles within the body. Out of our 650 muscles, 501 of them are skeletal muscle. Since they are bound to bone, they are mainly found at the legs, arms and chest.
– Smooth muscle: this kind of muscle is made up of elongated, smooth-looking fibers. They are also called involuntary because they are controlled unconsciously. They are activated by the autonomous nervous system and by hormones.
This type of muscle is also called visceral, because they are found in the internal organs (intestines, bladder, stomach) and blood vessels.
– Cardiac muscle: it is only found in the walls of the heart and its function is to enable the organ to contract automatically, at its own rate, around one hundred thousand times a day. It is striated in structure, but it is unlike skeletal and smooth muscle due to the position its fibers’ nuclei and their ramifications.
Also, these fibers have more mitochondria than the others, because the heart never stops working. Muscles contractions are longer and more frequent here, because if they come too close together the heart could get worn out. On top of that, it needs at least 5 second to contract once again.

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