Muscle
From Simple English Wikipedia, the free encyclopedia
Muscle is a tissue in animal bodies. Muscles are contractile tissue. This means they get shorter. When they get shorter, this is called contraction.
We use muscles to move our bodies. Many muscles pull on bones to make our arms and legs move.
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[edit] Types of muscles
There are three kinds of muscle:
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
Skeletal muscle moves our limbs (arms and legs.) It moves our jaw up and down so that we can chew food. Skeletal muscle is the only voluntary muscle. This means it is the only muscle that we can choose to move.
Cardiac muscle is the muscle in the heart. When this muscle contracts it pushes blood through our circulatory system. Cardiac muscle is not voluntary. You do not choose for your heart to contract.
Smooth muscle is other muscles in the body that are involuntary (not voluntary.) Smooth muscles are in many places. They are in:
- The gastrointestinal system – this includes the stomach and intestines. This is how food moves through us and we take energy from it.
- Blood vessels – smooth muscles make blood vessels smaller or bigger. This controls blood pressure.
- Hairs – smooth muscle in hair follicles makes your hair stand up when you are scared.
[edit] Muscle structure
Muscles are made of many muscle cells. The cells contract together to make the muscle get short. The muscle cells know to do this together because many of them get information sent to them by nerves. Then cells that get the message from nerves tell other cells that are near them. They tell the other cells by sending an electrical current.
Muscle cells are filled with proteins called actin and myosin. These are the proteins that make the muscle contract (get shorter.)
[edit] Muscle contraction
When a nerve tells a muscle to contract, the muscle opens holes in its cell membrane. These holes are proteins that are called calcium channels. Then calcium rushes into the cell. Calcium also comes out of special places in the cell where it is kept called the sarcoplasmic reticulum. This calcium sticks to the actin and myosin. This makes these proteins contract.
Contraction also needs ATP. This is the energy that your cells use. It is made from burning glucose in the cell. It takes very much energy to contract muscles. They use most of the energy your body uses.
[edit] Healthy muscles
Exercise makes muscles get bigger. Exercise also makes muscles stronger. If you do not exercise, your muscles atrophy. This means gets smaller and weaker.
[edit] Diseases of muscles
There are many different kinds of muscle diseases. There are three big groups of diseases:
- Neuromuscular diseases – these are problems with how the nerves tell the muscles to move. Strokes, cerebral palsy, and Parkinson's disease are neuromuscular diseases.
- Motor endplate diseases – these are problems with the place where the nerve tells the muscle to move. Tetanus and myasthenia gravis are motor endplate diseases.
- Myopathies – these are problems with the structure of the muscle. Muscular dystrophy, cancers like Ewing's sarcoma, and cardiomyopathy are myopathies.
