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Not to be confused with
Mussel.
Muscle is atissue in animalbodies. Muscles are basically tissue which may contract (shorten). They usually attach to bones and are the way animals move.
Their main purpose is to help us to move our body parts. They are one of the major systems of all animal bodies. When a muscle is activated it contracts, making itself shorter and thicker, thereby pulling its ends closer.
There are three kinds of muscles:
Muscle action can be classified as being eithervoluntary orinvoluntary.
Skeletal muscles, viewed from the front
Skeletal muscles, viewed from the back
The skeletal muscles move the limbs (arms and legs). They move thejaw up and down so that food can bechewed. Skeletal muscles are the onlyvoluntary muscles, the only ones that we can choose to move.
The cardiac muscle is the muscle in theheart. When this muscle contracts it pushes blood through thecirculatory system. The cardiac muscle isnot voluntary.
The smooth muscles are the other muscles in the body that are involuntary. Smooth muscles are in many places. They are in:
Muscles are made of many musclecells. The cells contract together to make the muscle get shorter. The muscle cells know to do this together because many of them get information sent to them bynerves. The cells that get the message from nerves tell other cells that are near them. They tell the other cells by sending anelectricalcurrent.
Muscle cells are filled withproteins calledactin andmyosin. These are the proteins that make the muscle contract (get shorter).
When a nerve tells a muscle to contract, the muscle opens holes in its cellmembrane. These holes are proteins that are calledcalcium channels. The calcium ions rush into the cell. Calcium also comes out of a special place in the cell called thesarcoplasmic reticulum. This calcium sticks to the specialized proteins actin and myosin. Thistriggers these proteins to contract the muscle.
Contraction also needsATP. This is the energy that your cells use. It is made from using glucose in the cell. It takes a lot of energy to release contracted muscles. They use most of the energy for building muscles.
Exercise makes muscles get bigger (seehypertrophy). Exercise also makes muscles stronger. If a person does not exercise, their muscles become smaller and weaker. This is calledmuscle atrophy.
There are many different kinds of musclediseases. There are three big groups of diseases:
- Neuromuscular diseases – these are problems with how the nerves tell the muscles to move.Strokes,cerebral palsy, andParkinson's disease are neuromuscular diseases.
- Motor endplate diseases – these are problems with the place where the nerve tells the muscle to move.Tetanus andmyasthenia gravis are motor endplate diseases.
- Myopathies – these are problems with the structure of the muscle.Muscular dystrophy,cancers likeEwing's sarcoma, andcardiomyopathy are myopathies.
What has muscles? All animals except the very simplest, and no other kind of living thing. Not trees, for instance.
