12. Muscles: Types and coordination

There are three types of muscles. They are:

  

  

The muscles of the body attached to the bones are known as skeletal muscles. They are also known as striated muscles. These are voluntary muscles as they can be controlled consciously by our will. The cells of these muscles are multinucleated, unbranched, and voluntary.

They are found attached to the bones found in the arms, legs, and neck.

 

 

  

They are also known as non-striated muscles or involuntary muscles, as our will does not control them. The cells of these muscles have a single, central nucleus.

 

These muscles are attached to soft parts of the body like blood vessels, iris, bronchi, digestive tract walls, urinary bladder, arteries, and the skin.

 

 

  

These are the muscles that make up the walls of the heart. They can perform continuous rhythmic contractions and are also involuntary in nature. These cells are branched and contain central nuclei.

 

 

This video is a summary of the muscular system of the human body.

 

A wide range of actions such as standing, walking, running, playing, tennis and so on require combined actions of multiple muscles. In order to perform a particular type of movement, the muscles have to be coordinated to a great extent. Muscles initiate movements by contracting and then relaxing. As discussed before, muscles can pull bones, but they can't push them back to the original position. Hence they work in pairs of flexors and extensors.

 

The muscles that contract to bend a limb at a joint are known as flexors. When the flexors relax, the extensor contracts to extend or straighten the limb at the same joint. The biceps muscle in front of the upper arm is a flexor and the triceps muscle at the back of the upper arm, is an extensor. When a person bends his elbow, the biceps contracts first, then the biceps relax, and finally the triceps contract to straighten the elbow.