Muscles

Muscles are the active part of the motor apparatus; their contraction produces various movements.

The muscles may be divided from a physiological standpoint into two classes: the voluntary muscles, which are under the control of the will, and the involuntary muscles, which are not.

All muscular tissues are controlled by the nervous system.

When muscular tissue is examined under the microscope, it is seen to be made up of small, elongated threadlike cells, which arc called muscle fibres, and which are bound into bundles by connective tissue.

There are three varieties of muscle fibres:

1) striated muscle fibres, which occur in voluntary muscles;

2) unstriated muscles which bring about movements in the internal organs;

3) cardiac or heart fibres, which are striated like (1), but are otherwise different.

Muscle consists of threads, or muscle fibers, supported by connective tissue, which act by fiber contraction. There are two types of muscles smooth and striated. Smooth, muscles are found in the walls of all the hollow organs and tubes of the body, such as blood vessels and intestines. These react slowly to stimuli from the autonomic nervous system. The striated, muscles of the body mostly attach to the bones and move the skeleton. Under the microscope their fibres have a cross – striped appearance. Striated muscle is capable of fast contractions. The heart wall is made up of special type of striated muscle fibres called cardiac muscle. The body is composed of about 600 skeletal muscles. In the adult about 35–40 % of the body weight is formed by the muscles. According to the basic part of the skeleton all the muscles are divided into the muscles of the trunk, head and extremities.

According to the form all the muscles are traditionally divided into three basic groups: long, short and wide muscles. Long muscles compose the free parts of the extremities. The wide muscles form the walls of the body cavities. Some short muscles, of which stapedus is the smallest muscle in the human body, form facial musculature.

Some muscles are called according to the structure of their fibres, for example radiated muscles; others according to their uses, for example extensors or according to their directions, for example, – oblique.

Great research work was carried out by many scientists to determine the functions of the muscles. Their work helped to establish that the muscles were the active agents of motion and contraction.

Date: 2016-02-19; view: 496; Нарушение авторских прав