11th Class Biology Locomotion and Movement Body Muscles

In the body of all the multicellular animals muscles are found. The movement of the body takes place by these muscles. If the muscles become weak, the functioning of the body become difficult. The muscles are capable of contraction and relaxation, hence these are elastic.

A muscle can pull a part of the body by its contraction (shortening). It cannot push that part by relaxation (elongation). Hence, the muscles are typically arranged in antagonistic (opposing) pairs, one muscle moves a body part in one direction by its contraction and the other muscle moves that part in the opposite direction by its contraction. Of course, when one muscle contracts, its opposing muscle relaxes. The principle of antagonistic muscles is true of both vertebrate as well as invertebrate muscles. Animal movements depend upon interaction of muscles and skeleton.

(1) Action of body muscles : As mentioned above, the body muscles are arranged in antagonistic (opposing) pairs. One muscle of a pair moves a body part in one direction and the other in the opposite direction. For example, the muscle named biceps brings the forearm toward the upper arm, and the muscle called the triceps moves the forearm away from the upper arm. When biceps contracts to cause movement, the triceps relaxes to allow that movement to occur and vice versa. Similar pairs of opposing flexor and extensor muscles occur at the wrist, ankle and knee. The type of movement that results from the contraction of a muscle depends entirely upon the way the muscle is attached to the levers of the skeleton.

(2) Classification of body muscles : According to the type of motion they cause, the muscles are divided into the following types. The muscles that act together to produce a movement are called synergists and the muscle that act in opposition to each other are antagonists. The muscles that act most powerfully during any given movements are called prime movers.

(i) Flexor and Extensor : Muscles that bend one part over another joint is called flexor. Extensor muscle is antagonist of flexor muscle. The contraction of an extensor extends a joint by pulling one of the articulating bone apart from another.

(ii) Pronator and Supinator : The contraction of a pronator rotates the forearm to turn the palm downward or backward. Supinator is antagonist of pronator. A supinator contracts to rotate the forearm and thus to make palm face upward or forward.

(iii) Abductor and Adductor : An abductor contracts to draw a bone away from the body midline. Muscle that brings the limb away from midline is called abductor. An adductor draws a bone towards the body midline. Muscles that brings the limb towards midline is called adductor. Abductor muscle is antagonist of adductor muscle. Abduction is elevation and adduction is depression.

(iv) Protractor and Retractor : Protractor muscle pulls the lower jaw, tongue and the head forward. Retraction is opposite to protaction. Retractor muscle draws the lower jaw, tongue and the head backward.

(v) Inversion and Eversion : Turning of feet so that the soles face one another in inversion. Eversion is the opposite of inversion. In this movement, the soles of the feet face laterally.

(vi) Rotation : Rotation is term that indicates the partial revolving of a body part on the part's long axis.

(vii) Arrector : Raises hairs of skin.

(viii) Levator : Elevates a part of body.

(ix) Depressor : Lowers a part of body.

(x) Agonistic : Opposed in action by another muscle.

(xi) Antagonistic : Counteracts the action of another muscle.

(xii) Sphineter : Closes a natural orifice or passage.

(xiii) Constrictor : Causes constriction or squeezing.

The adductor and abductor, elevator and depressor, pronator and supinator, and sphincters and dilators are all antagonistic muscles.

Important muscles

In man total no. of muscles : 656 muscles