Human muscles - What is their function?

In some parts of the body there are cells that can shrivel or relax – these are the muscle cells.
There are two types:  

• smooth and 
• striated.

Smooth muscles are found in many parts of the body and support the work of almost all organs: they contract and expand the pupil of the eye, regulate breathing and so on. Contraction of smooth muscle is strong, but slow.

Where is necessary to move quickly, are located the striated muscle cells. All the muscles that move our limbs are striated.

The human body has 639 muscles. 

• Muscles are actually fleshy parts of the body.

• Meat purchased from a butcher is striated muscle.

• Muscles are in different sizes and different shapes.

Medium sized muscle is consisted of about ten million of muscle cells, and the whole body from about six billion muscle cells!
Each of the six billion of muscle-like cells, is similar to ten-cylinder engine arranged in a single row. Cylinders are tiny boxes containing liquid. Muscle twitches when the brain sends a message to the muscle boxes. For a fraction of a second fluid in such a tiny box thickens: and then becomes liquid again. This leads to contraction and relaxation of muscles.

The muscles in our body, which we can consciously move are the striated. Smooth muscles (such as those involved in the digestion of food) are independent of our will.

When a muscle is stimulated to act, it reacts quickly: it can shrivel to less than a tenth of a second.
But before it gets to relax, it gets another message, so it writhes and convulses again.
Contractions occurred so rapidly that merge into a single action, as evidenced by the smooth and continuous operation of muscles.

How do muscles work?

Muscles are made of tough, elastic tissue.
 They are built so that they can contract, which means that they become shorter.
When the muscles whose ends are joined to bones contract, they pull at the bones and make them move.
Muscles are made up of long, thin cells that join together to make muscle fibers. When the muscle becomes shorter, all the fibers move closer together, making the muscle bulge.
You can see your muscles bulging and relaxing when you move your arms and legs. If you bend your elbow and clench your fist, the muscles called biceps in your upper arm will bulge.

Muscles can only pull—they can’t push. 

Muscles whose ends are joined to bones work in pairs. One muscle contracts and pulls the bone one way, and the other contracts to pull the bone back again.

Interesting Facts About Muscles

• Human muscle cells produce enough heat every day to boil almost 2 pints of water for an hour.
• The tongue is the strongest muscle in the human body. 
• Muscles make around 40% of human body weight.
• We utilize more than 200 muscles just to make one step.
• The foot is responsible for one quarter of all the human body’s muscles
• Fingers do not have muscles in them, since they are moved by tendons and attached to muscles in the forearm. 
• When we shiver, our muscles contract involuntarily and this releases energy that keeps the body warm.
• The heart beats more than 4500 times each hour since the cardiac muscle never gets tired.  While sleeping, playing sport, resting even when going into the toilet, the hearth beats on average 80 beats per minute. 
• While smiling, we are using about 30 muscles, which control the eyelids, nostrils and brow, working together to show emotions.