Muscle and Movements
Earlier you have read about amoeboid movement, ciliary and flagellar movement. In this section you will learn how muscles are involved in the movement. Muscle cells are found in almost all the phyla of the animal kingdom except the phylum protozoa. Contraction and relaxation of these muscles brings about movement in the organisms. In vertebrates there are three types of muscles: skeletal muscles, cardiac muscles and smooth muscles. Skeletal muscles are attached to the bones in the arms, legs and the spinal cord and produce activities such as walking, movement of head, hands etc. Cardiac muscles are the muscles of the heart. These are specialised for continuous contractions of the heart, needed in pumping of the blood.
Smooth muscles are present in the walls of internal organs such as the large and small intestine, the gall bladder and large blood vessels. Contraction and relaxation of smooth muscles control the diameter of blood vessels and also propel food along the gastro-intestinal tract. Under the microscope the skeletal muscles and the cardiac muscles exhibit transverse light and dark bands alternating with each other. Therefore, the skeletal muscles and the cardiac muscles are also called striated muscles. The smooth muscles do not have striations.