Muscles
Types of muscles
There are different types of muscles, depending on the cells that make them up and the function they perform within the body.
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.
Muscle location
Depending on where they are, muscles are classified into superficial or cutaneous and deep. The former are near the skin (along the face, head and neck). They are long and can pass through several joints. Deep muscle is inserted into the bones of the skeleton and in some organs, like the sensory organs. They are short and only cover a single joint.
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Other classifications
Muscles can also be classified according to other parameters.
- Long: they are long, flat and very strong. For example, biceps.
- Short: they are short in length. For example, the muscles of the head and neck.
- Orbicular: they are more or les shaped like a circle and are found at important areas, like the mouth are eyelids.
- Broad: they are usually thin and flat. Their diameter is normally the same as their length.
- Flexors: they allow flexing of all four limbs.
- Extensors: they stretch the limbs.
- Pronators: they twist limbs inward.
- Supinators: they allow supination of the limbs or putting our forearms palms-up.
- Abductors: they are in charge of pulling the limbs away from our middle plane. For example, opening our legs.
- Adductors: they pull the limbs in towards the body. For example, putting our elbow near our navel.
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Duchenne muscular dystrophy (DMD)
A study published by American magazine Genes and Development showed that administering an agent that decreases fibrinogen in muscle tissue produces a drop in muscular fibrosis and an improvement in the treatment of muscular dystrophy.
DMD is degenerative muscular disease caused by a lack of a protein called dystrophin in male children.
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Movable muscle
In order for a muscle to move correctly, it must have flexibility and good muscle tone. Flexibility consists on the ability to bend and stretch the body's limbs through constant use of our muscles and joints. Good muscle tone is achieved when a muscle reacts quickly to any form of stimulation, considering tension, firmness and elasticity.
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PALABRAS CLAVE
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Muscle fiber