Movement is an essential function of the body resulting from muscle contractions and relaxation.
With the exception of sponges and some coelenterates, which have no muscle tissue, all other animals use muscles to move their bodies.
It is thanks to the muscular contraction that animals can swim, breathe, fly, swim, move food in the digestive cavity, pump blood into blood vessels etc.
Muscle tissue accounts for 40% to 50% of total body weight and is composed of highly specialized cells. Muscles are primarily related to the functions of movement, posture maintenance and heat production.
It has been estimated that 85% of all heat generated in the body comes from muscle contractions.
Muscle tissue types
Muscles can be formed by three basic types of muscle tissue: skeletal striated, smooth, and cardiac striated.
Skeletal striated muscle
Skeletal striated muscle tissue has, under microscopic observation, alternating transverse bands, light and dark. This striation results from the regular arrangement of microfilaments formed by the actin and myosin proteins responsible for muscle contraction. The striated muscle cell, also called muscle fiber, has numerous nuclei and can reach lengths ranging from 1mm to 60 cm.
Smooth muscle tissue is present in various internal organs (digestive tract, bladder, uterus, etc.) and also in the walls of blood vessels. Smooth muscle cells are uninucleated and the actin and myosin filaments are helically disposed inside without striatal pattern as in skeletal muscle tissue.
Contraction of smooth muscles is usually involuntary, unlike contraction of skeletal muscles, which is under the control of the will.
Cardiac striated muscle
Cardiac muscle tissue is present only in the heart of vertebrates. Under the microscope, cardiac muscle tissue shows transverse striations. Its cells are uninuclear and have involuntary contraction.