Locomotion and Movement — Class 11 Biology

This chapter studies the types of movement in the human body and the muscular and skeletal systems that make locomotion possible. Cells show amoeboid, ciliary and muscular movements; locomotion is a voluntary movement that changes the location of the animal. Muscle is a tissue of mesodermal origin with the properties of excitability, contractility, extensibility and elasticity, classified by location into skeletal (striated, voluntary), visceral (smooth, involuntary) and cardiac muscle. A skeletal muscle is made of bundles of muscle fibres, each containing myofibrils with sarcomeres, the functional units bounded by Z lines and made of thin actin and thick myosin filaments. According to the sliding filament theory, contraction occurs when the thin filaments slide over the thick filaments: a nerve signal releases calcium, which exposes binding sites so that myosin heads form cross bridges and pull the actin filaments inward, shortening the sarcomere. Muscles may be red (aerobic, with myoglobin) or white (anaerobic). The skeletal system has 206 bones grouped into the axial skeleton (skull, vertebral column, ribs, sternum) and the appendicular skeleton (limb bones and girdles). Joints, the points of contact between bones, are fibrous, cartilaginous or synovial, the last allowing free movement. Disorders include myasthenia gravis, muscular dystrophy, tetany, arthritis, osteoporosis and gout.