| General| Antagonistic Muscles| Levers| Types of Levers|


Bones are required for movement and locomotion, but they are unable to move on their own. They must be move by the alternate contraction and relaxation of the skeletal muscles. Many bones have ridges and protuberances which provide an area for muscle attachment. Skeletal muscles act on the bones that serve as a system of levers. Movements of various parts of the body may result in locomotion of the body as a whole.

Antagonistic Muscles.

For every muscle or group of muscles that brings about movement of a certain part of the body, there is another muscle or group of muscles which bring about an opposite movement. Such muscles, bringing about opposite movements, are called antagonistic muscles. They make the smooth co-ordination of movement possible. As the one muscle contracts, the other (which is able to bring about an opposite movement) will relax, and vice versa.

Diagram showing the action of the biceps (flexor) muscles and the
triceps (extensor muscles) .


Movement in the higher developed multicellular animals is brought about by the muscles which form a system of levers in conjunction with the bones of the skeleton. Movement of the levers is possibe because of joints and the contraction of muscles which are attached to the levers.

A lever is an inflexible or rigid rod that is able to rotate about a fixed point called the fulcrum.
A simple lever system.