The Basic Types of Movements
There are three basic types of movements namely amoeboid, ciliary and muscular.
Amoeboid movement is typical of Amoeba, which performs the function of locomotion by producing pseudopodia, involving changing in shape of the cell body and streaming movement of cytoplasm. Amoeboid movement helps in capture of food and change of place as well.
Ciliary movement occurs in protozoans such as Paramecium which use their cilia to procure food. Ciliary lining of human respiratory tract also drives off microbes and dust particles attached to the respiratory tract.
Muscular movement occurs in vertebrates which involves the contraction and relaxation of muscles that bring about the locomotion.
The Skeletal System
The skeletal system consists of the different bones in the body and this system forms the framework of the body. A familiarity with the names, shapes and positions of individual bones will help in understanding of some of the other organ systems. For example, movements such as a throwing a ball, typing and walking require the coordinated use of bones and muscles. To understand how muscles produce different movements, we need to learn the parts of bones to which the muscles are attached. Many bones serve as landmarks to students of anatomy as well as to surgeons. Blood vessels and nerves often run parallel to bones. These structures can be located more easily if the bone is identified first.
The functions of the skeletal system can be summarised as follows:
- The skeleton gives shape to the body.
- It protects the important internal organs such as the heart, lungs, the brain etc.
- The bones serve as attachment surfaces for muscles and thus provide suitable level for locomotion.
- The bone marrow found in the hollow cavity of long bones produces red blood cells.
Types of Bones
Almost all the bones in the body can be classified into four principal types, namely long bones, short bones, flat bones and irregular bones.
Long bones have greater length than width. They are slightly curved for strength. A curved bone is structurally designed to absorb the stress of the body weight at several different points so that the stress is evenly distributed. Examples of long bones include bones of the thighs, legs, toes, arms, forearms and fingers.
Short bones are somewhat cube-shaped and are equal in length and width. Their texture is spongy except at the surface, where there is a thin layer of compact bone. Examples of short bones are the wrist and ankle bones.
Flat bones are generally thin and composed of two more or less parallel plates of compact bone enclosing a layer of spongy bone. Flat bones afford considerable protection and provide extensive areas for muscle attachment. Examples of the flat bones include the cranial bones, which protect the brain, and the sternum and ribs, which protect organs in the thorax and scapulas.
Irregular bones have complex shapes and cannot be grouped into any of the three categories just described. They also vary in the amount of spongy and compact bone present. Such bones are the vertebrae and certain facial bones.
Wormian or sutural bones are small clusters of bones between the joints of certain cranial bones. Sesamoid bones are small bones in tendons where considerable pressure develops. The patella or kneecaps are examples of sesamoid bones.
The bones of a child are more flexible and less brittle than those of an adult. The bones of children contain large quantities of organic matter and very little of salts. With the advance in age, more and more calcium phosphate is deposited in the bones and the content of organic substances diminishes in quantity. This makes the bones harder and brittle. Old people are, thus, more liable to fracture their bones.