Locomotion and Movement

Movement is a defining feature of living things, but not every movement is locomotion. Locomotion is the movement of the whole body from one place to another (walking, running, swimming); all locomotion is movement, but not all movement is locomotion. Human cells show three kinds of movement, a standard NEET fact. Amoeboid movement uses temporary pseudopodia formed by streaming of the cytoplasm (and microfilaments); it is seen in leucocytes (WBCs) and macrophages. Ciliary movement is the beating of cilia lining internal tubes — it moves mucus and dust in the trachea and moves the ovum along the female reproductive tract. Muscular movement uses the contraction of muscles and moves the limbs, jaws and tongue; it is the basis of locomotion.

Muscle makes up about 40–50% of the body weight and has special properties: excitability (responds to stimuli), contractility, extensibility and elasticity. On the basis of location, structure and control there are three muscle types, and telling them apart is heavily examined.

Skeletal (striated) muscle is attached to bones, shows clear cross-striations, is voluntary (under conscious control) and tires with continuous use. Smooth (non-striated, visceral) muscle lies in the walls of internal organs such as the gut, blood vessels and uterus; it has no striations, is involuntary and spindle-shaped. Cardiac muscle is found only in the heart; it is striated like skeletal muscle but involuntary like smooth muscle, and its branched fibres are joined by intercalated discs so the heart contracts as one unit and does not fatigue.

For NEET, lock in the three movement types with their examples and the three muscle types with their three key features each (location, striation, control). The cross-comparison — cardiac muscle being striated yet involuntary — is a favourite trap.

A skeletal muscle is built of bundles called fascicles, each holding many muscle fibres (the cells). Each fibre is a syncytium (multinucleate) and is packed with myofibrils; the cell membrane is the sarcolemma, the cytoplasm the sarcoplasm, and the calcium-storing endoplasmic reticulum the sarcoplasmic reticulum. The striations come from a regular pattern of bands along each myofibril. The dark A band (anisotropic) contains the thick myosin; the light I band (isotropic) contains the thin actin. A thin Z line bisects each I band, and the region between two successive Z lines is the sarcomere — the functional unit of contraction. The central lighter part of the A band, where actin does not reach, is the H zone.

The thin filament is two strands of F-actin with tropomyosin and the troponin complex wound along them; at rest tropomyosin masks the actin sites where myosin would bind. The thick filament is myosin, whose globular heads (cross-bridges) have both an ATPase and an actin-binding site.

Contraction is explained by the sliding-filament theory: the thin filaments slide over the thick filaments toward the centre of the sarcomere, so the sarcomere shortens — the filaments themselves do not shorten. The trigger is a nerve signal that releases Ca²⁺ from the sarcoplasmic reticulum; Ca²⁺ binds troponin, shifting tropomyosin to expose the actin binding sites. The myosin heads then attach, swivel to pull the actin inward (the power stroke), and detach and re-attach repeatedly — a cycle powered by ATP.

The visible result during contraction is the must-know point: the sarcomere, the I band and the H zone all shorten, while the A band stays the same length (because the thick filaments do not change). When the signal stops, Ca²⁺ is pumped back, tropomyosin re-masks the sites and the muscle relaxes. For NEET, fix the band identities (A = myosin/dark, I = actin/light, Z bisects I, sarcomere between Z lines), the filament make-up, the requirement for Ca²⁺ and ATP, and exactly which bands change.

The skeletal system is the framework of bones and cartilages; it supports the body, protects organs, gives attachment to muscles for movement, makes blood cells (in marrow) and stores minerals. The adult human skeleton has 206 bones, divided into the axial and appendicular skeletons — a division and its bone counts are classic NEET recall.

The axial skeleton (80 bones) forms the main axis. It includes the skull (22 bones — 8 cranial + 14 facial), the middle-ear ossicles (6, three per ear), the single hyoid, the vertebral column (26 vertebrae), the sternum (1) and the ribs (12 pairs = 24). The vertebral column is worth memorising: 7 cervical, 12 thoracic, 5 lumbar, 1 sacrum (fused from 5) and 1 coccyx (fused from 3–4) — it protects the spinal cord. Of the ribs, pairs 1–7 are true (vertebrosternal) ribs joined to the sternum, pairs 8–10 are false (vertebrochondral) joined indirectly, and pairs 11–12 are floating, not joined in front.

The appendicular skeleton (126 bones) is the limbs plus their girdles. Each forelimb has the humerus, radius and ulna, carpals, metacarpals and phalanges; each hindlimb has the femur (the longest bone), tibia and fibula, patella (knee cap), tarsals, metatarsals and phalanges. The limbs attach to the trunk through girdles: the pectoral girdle (each half = a clavicle + a scapula) for the arms, and the pelvic girdle (the hip bones, each made of fused ilium, ischium and pubis) for the legs.

For NEET, the high-yield numbers are: 206 total = 80 axial + 126 appendicular; skull 22; vertebrae 26 (7+12+5+1+1); ribs 12 pairs (true 1–7, false 8–10, floating 11–12); and the make-up of the two girdles. The next topic links these bones at their joints.

Joints are the points where two or more bones (or bone and cartilage) meet; they are essential for all movement, since muscles can only move the body by acting across joints. Joints are classified by how much movement they allow into three groups, a standard NEET set. Fibrous joints are held by dense fibrous tissue and are immovable — the best example is the sutures of the skull. Cartilaginous joints are joined by cartilage and allow only limited (slight) movement — for example the joints between adjacent vertebrae of the vertebral column.

Synovial joints are freely movable and are the most important for locomotion; the bone ends are capped with cartilage and separated by a cavity filled with lubricating synovial fluid. They come in several sub-types: the ball-and-socket joint (the most mobile, allowing movement in all planes) at the shoulder and hip; the hinge joint (movement in one plane) at the knee and elbow; the pivot joint (rotation) between the atlas and axis of the neck; the gliding joint between the carpals; and the saddle joint at the base of the thumb.

Several disorders of the muscular and skeletal systems complete the chapter and are frequently asked. Myasthenia gravis is an autoimmune disorder affecting the neuromuscular junction, causing weakness and paralysis of skeletal muscle. Muscular dystrophy is a group of inherited diseases with progressive degeneration of skeletal muscle. Tetany is rapid, painful muscle spasms (wild contractions) caused by a fall in blood calcium (Ca²⁺).

Among skeletal disorders, arthritis is inflammation of the joints; osteoporosis is an age-related decrease in bone mass and density (with greater risk of fractures), linked to a fall in oestrogen levels especially after menopause; and gout is the inflammation of joints due to the deposition of uric-acid crystals. For NEET, fix the three joint classes with examples (sutures = fibrous/immovable; between vertebrae = cartilaginous; shoulder/hip = ball-and-socket; knee/elbow = hinge) and match each disorder to its precise cause — especially myasthenia gravis (autoimmune, neuromuscular junction), tetany (low Ca²⁺), osteoporosis (low oestrogen) and gout (uric acid).