How Muscles move Bones in Mammals

Muscles are attached to bones at two points. One end of a block of muscles is usually attached to an immovable bone, e.g the shoulder blade, and the other end to a movable bone, e.g. the radius first point of attachment is known as the origin of the muscle and the second as its insertion. Muscles may be attached directly to the bone or directly by means of tendons. Muscles may have more than one origin.

    Muscles can only contact and relax, but to expand. When a muscle contracts, it becomes shorter and thicker, and pulls on the bone to which it is attached. A muscle cannot push on a bone. When a muscle relaxes, it lengthens and becomes thinner. Most muscles act in parts such that when one member of a pair contracts, the other relaxes. This produces movement of a bone in one direction. When the reverse happens, the bone moves in the opposite direction. Such muscle pairs are known as antagonistic muscles. A pair of antagonistic muscles consist of 

• An extensor which straightens a limb by its contraction, and 

• A flexor which bends it.

This shows how two important muscles of the upper arm, the biceps and triceps muscles, bring about the bending and straightening of the lower arm.

    When a rabbit is in a crouching position, the extensor muscles are relaxed and the flexor muscles contracted. When danger threatens and the rabbit Is about to jump the extensor muscles contract and the flexors relax. Movement, thereafter, consists of a series of contractions and relaxation of the muscles.

     Bones can be likened to levers upon which muscles can act in most cases, the muscles act on the bones in such a way that they behave as levers with a low mechanical advantage. all the three orders of levers occur in the mammalian body. During the bending the lower arm , a small contraction of the biceps muscle (the effort) produces a large movement of the lower arm (the load) around the elbow joint (the fulcrum). Thus,  the biceps muscle of the arm may only contract about 2•5cm but it can move the lower arm through a distance of about 30cm.

    When effort is applied ( muscle contraction), work is done (limb movement). The force to do work comes from muscular energy obtained by the oxidation of glycogen stored within the muscle. Thus. Muscular energy is derived from the chemical energy.