Difference Between Muscle And Connective Tissue
The second large group of tissues is the muscles, made up of bundles of highly active, long, and slim muscle cells or filaments. When these cells contract in unison, they are capable of moving the bones to which their ends are attached.
The body contains over 600 different muscles, but they can all be classified as one of three kinds: smooth, skeletal, and cardiac. Smooth, or visceral, muscle is found in the viscera, or internal organs, of the body. Smooth muscle is spread in delicate strands and sheets throughout the lining of the stomach and intestine, the urinary and reproductive organs, the blood vessels, the respiratory system, and elsewhere. It is controlled by the autonomic nervous system—that is, it provides for movements that are not under the mind’s conscious control but that are indispensable for various bodily functions. These movements include the shrinking of the pupil of the eye in response to bright light.
Skeletal muscle is more familiar, perhaps because the movements of these bundles of filaments can be controlled. Skeletal muscle is attached to and moves the bones of the skeleton. For example, the skeletal muscles that go down the back hold the backbone and head in place. In the upper arm and upper leg, large muscles open and close the elbow and knee joints. Attached to the forearm and foreleg are the muscles used for manipulating the hand and foot. Numerous small muscles control the intricate movements of the fingers and toes. The long cells of skeletal muscle contain large numbers of filaments called myofibrils, which run lengthwise through the cytoplasm. They are marked with alternating dark and light bands.
Cardiac muscle is found in the heart. Here the cells are joined end-to-end in a continuous branching network—that is, each cell is directly connected to its neighbors. Each cardiac-muscle fiber, however, contracts and relaxes at its own rate. A small mass of tissue within the heart, called the pacemaker, coordinates these movements to produce a wave that starts with one cell and moves through each neighbor cell to produce the regular, rhythmic pumping action of the heart. Like smooth muscle, the action of cardiac muscle cannot be controlled by the conscious mind.
Blood, bones, cartilage, tendons, ligaments, and adipose, or fatty, tissue are types of connective tissue. With the exception of blood, the main functions are to support, bind, reinforce, and protect other tissues; adipose tissue also insulates the body and stores energy. Connective tissue is characterized by a large number of similar cells dispersed in a noncellular medium called a matrix. The matrix varies in consistency, from fluid to solid. Its properties differ in different tissue types.
The matrix of bone is hardened by minerals, particularly calcium salts, which give bone its solidity and strength. Another type of supporting connective tissue is cartilage, which is more flexible than bone. At the other extreme is blood, in which red blood cells and white blood cells are suspended in a watery matrix called blood plasma.
Fibrous connective tissues are packed with collagen fibers that offer toughness, strength, and elasticity. Ligaments, which connect one bone to another, and tendons, which attach muscles to bones, are examples. The inner layer of the skin also has connective tissue that contains many elastic fibers.