The skeletal muscles are made up of bundles of muscle fibres. These muscles are attached to the bones of the skeleton to affect movement. Movements of the body are brought about by the contraction of a pair of antagonistic muscles. Energy for this contraction comes from ATP produced in the mitochondria in the muscles. Muscles which contract when receiving impulses from the brain are known as voluntary muscles.
Muscles are attached to the bones by tendons. A tendon is a chord of dense connective tissues made up of fibres. These fibres are strong and elastic. At the joints, the bones are held together by ligaments which are flexible, strong and elastic connective tissue. This allows two bones to bones to be held together and permits limited movement but at the same time, ensures that the bones do not become mal-aligned or dislocated.
Since muscles can only contract, at least two muscles must be used to move a bone into a position and back again. All skeletal muscles exist in pairs and they act as antagonistic pairs, meaning when one member of a pair of muscles contract, the other must relax. As an example, the movement of the forelimb is brought about by the contraction and relaxation of a pair of antagonistic muscles, namely the biceps and the triceps.
When the biceps muscle contracts, the triceps muscle relaxes resulting in the arm being bent. Conversely, to straighten the arm, the triceps muscle contracts while the biceps muscle relaxes. Contraction of the biceps muscle pulls the ulna up thus bending the arm at the elbow joint. Contraction of the triceps muscle pulls the ulna down and the arm is straightened.
