Revision: Class 11 >> Locomotion and Movement NEET (UG) Locomotion and Movement

Locomotion is the voluntary movement of an individual from one place to another.

• Locomotion is the movement of a living being from one place to another (e.g., walking, running, swimming).
• All locomotion is movement, but not all movements are locomotion (e.g., blinking or moving limbs without changing place).
• Movement is a basic feature of living organisms, seen in both plants and animals (e.g., Amoeba shows protoplasmic streaming).
• Different organisms use different structures for movement, like cilia, flagella, tentacles, and limbs.
• The purpose of locomotion includes finding food, shelter, mates, suitable conditions, and escaping predators.

• Human body cells show three types of movements: Amoeboid, Ciliary, and Muscular.
• Amoeboid movement - caused by pseudopodia; involves microfilaments; seen in leucocytes and macrophages.
• Ciliary movement - occurs in organs lined by ciliated epithelium; removes dust in the trachea; moves ova in the fallopian tube.
• Muscular movement - due to the contractile property of muscles; seen in jaws, limbs, eyelids, alimentary canal, and ureters.
• Muscular movement is used for locomotion and other movements in humans and most multicellular organisms.
• Locomotion requires coordinated activity of muscular, skeletal, and neural systems.

• Muscles are specialised tissues of mesodermal origin and contribute to 40–50% of an adult human's body weight.
• Muscles have four properties - Excitability, Contractility, Extensibility, and Elasticity.
• Skeletal muscles — associated with the skeletal system; striated (light & dark bands); voluntary; responsible for locomotion and body posture changes.
• Visceral muscles — form the inner walls of internal organs; non-striated; involuntary; assist in the movement of food through the digestive tract and gametes.
• Cardiac muscles - found only in the heart; striated with a branching pattern; involuntary in action.

• Skeletal muscle is made up of muscle bundles (fascicles) held together by fascia (collagenous connective tissue). Each bundle contains many muscle fibres.
• Each muscle fibre is lined by sarcolemma, contains sarcoplasm, is a syncytium (many nuclei), and the sarcoplasmic reticulum stores calcium ions.
• Muscle fibres contain myofibrils with alternate light and dark bands due to actin and myosin proteins.
• I-band - light, contains thin actin filaments. A-band - dark, contains thick myosin filaments.
• 'Z' line - bisects each I-band; thin filaments are attached to it. 'M' line - in the middle of the A-band; holds thick filaments together.
• Sarcomere - region between two successive 'Z' lines; functional unit of contraction.
• In the resting state, thin filaments partially overlap thick filaments; the non-overlapped part of the thick filament is the 'H' zone.

• Each thin filament (actin) is made of two 'F' (Filamentous) actins helically wound together. Each 'F' actin is a polymer of monomeric 'G' (Globular) actins.
• Two tropomyosin filaments run alongside 'F' actins. Troponin proteins are distributed at regular intervals on tropomyosin.
• In the resting state, a troponin subunit masks the active binding sites for myosin on actin filaments.
• Each thick filament (myosin) is made of many monomeric proteins called meromyosins. Each meromyosin has a globular head, short arm, and tail.
• Meromyosin is of two types - HMM (Heavy Meromyosin) - the globular head + short arm, and LMM (Light Meromyosin) - the tail.
• The globular head (HMM) projects outward, forming a cross arm. It acts as an active ATPase enzyme and has binding sites for both ATP and actin.

• Muscle contraction follows the sliding filament theory, where thin (actin) filaments slide over thick (myosin) filaments.
• Contraction begins with a signal from the CNS through a motor neuron; the neuron and muscle fibres together form a motor unit.
• The neuromuscular junction (motor-end plate) is the point where the motor neuron connects to the muscle fibre.
• Acetylcholine is released, which generates an action potential and causes the release of Ca²⁺ from the sarcoplasmic reticulum.
• Calcium ions activate actin, allowing myosin heads to bind and form cross-bridges.
• Cross bridges pull actin filaments, causing sliding, shortening of the sarcomere, and muscle contraction (I-band shortens, A-band remains the same).
• ATP helps in breaking and reforming cross-bridges; when Ca²⁺ is pumped back, the muscle relaxes.

• The skeletal system consists of bones and cartilage and provides shape and support to the body.
• It plays an important role in movement, along with the muscular system (e.g., jaw for chewing, limbs for walking).
• Bones are hard due to calcium salts, while cartilage is flexible due to chondroitin salts.
• Humans have 206 bones in adulthood, while a newborn has about 300 bones that fuse during growth.
• The skeletal system is divided into two parts: the axial skeleton and the appendicular skeleton.

• The axial skeleton has 80 bones and forms the main axis of the body (head and trunk).
• It includes the skull, vertebral column, ribs and sternum.
• Skull has 22 bones → 8 cranial (protect the brain) and 14 facial (form the face); also includes the hyoid bone and ear ossicles (malleus, incus, stapes).
• The vertebral column has 26 vertebrae and protects the spinal cord; the first vertebra is the atlas.
• The vertebral column is divided into cervical (7), thoracic (12), lumbar (5), sacral (1 fused) and coccygeal (1 fused) regions.
• Ribs are 12 pairs → 7 true ribs, 3 false ribs, and 2 floating ribs.
• The rib cage (ribs + sternum + thoracic vertebrae) protects vital organs like the heart and lungs.

• The appendicular skeleton includes bones of the limbs and their girdles. Each limb has 30 bones.
• Upper limb - Humerus, Radius, Ulna, 8 Carpals, 5 Metacarpals, 14 Phalanges.
• Lower limb - Femur, Patella (kneecap), Tibia, Fibula, 7 Tarsals, 5 Metatarsals, 14 Phalanges.
• Pectoral girdle - Clavicle + Scapula; glenoid cavity of scapula articulates with humerus → shoulder joint.
• Pelvic girdle - two coxal bones, each formed by fusion of ilium + ischium + pubis; the acetabulum articulates with the femur.
• The two pelvic halves are joined by the pubic symphysis (fibrous cartilage).

• Joints connect bones and help in body movement.
• They act as points of contact between bones or between bone and cartilage.
• Muscles act on joints like a fulcrum to produce movement.
• Joints are of three types: fibrous, cartilaginous and synovial.
• Fibrous joints → no movement (e.g., skull sutures).
• Cartilaginous joints → limited movement (e.g., between vertebrae).
• Synovial joints → free movement (e.g., ball & socket, hinge, pivot).

• Myasthenia gravis - an autoimmune disorder affecting the neuromuscular junction; causes fatigue, weakness, and paralysis of skeletal muscles.
• Muscular dystrophy - progressive degeneration of skeletal muscles; mainly caused by a genetic disorder.
• Tetany - rapid spasms/wild contractions in muscles due to low Ca²⁺ (calcium) levels in body fluids.
• Arthritis - inflammation of joints causing pain and stiffness.
• Osteoporosis - an age-related disorder; decreased bone mass and increased risk of fractures; caused by a decrease in oestrogen levels.
• Gout - inflammation of joints due to the accumulation of uric acid crystals; causes intense pain and swelling.