Chapter overview: movement and locomotion
Movement is a fundamental feature of living organisms. Locomotion is a voluntary movement that produces a change of place. Thus, all locomotion is movement, but all movement is not locomotion.
Why animals locomote To search for food, shelter, mate, breeding grounds or favourable climate, and to escape enemies or predators. Locomotion needs coordinated muscular, skeletal and neural activity.
17.1 Types of movement in humans
| Type | How it occurs | Examples / function |
|---|---|---|
| Amoeboid | Streaming of protoplasm produces pseudopodia; microfilaments are involved. | Macrophages and leucocytes. |
| Ciliary | Coordinated beating of cilia in ciliated epithelium. | Tracheal cilia remove dust and foreign particles; cilia help move ova through female reproductive tract. |
| Muscular | Contraction of muscle tissue. | Movement of limbs, jaws and tongue; locomotion and posture. |
| Flagellar | Movement of membrane outgrowths called flagella. | Sperm swimming, water current in sponges and locomotion of Euglena. |
17.2 Muscle: properties and types
Muscle is specialised tissue of mesodermal origin and contributes about 40-50% of adult body weight. Its key properties are excitability, contractility, extensibility and elasticity.
| Muscle type | Location / appearance | Control and role |
|---|---|---|
| Skeletal | Attached to skeletal components; striated. | Voluntary; locomotion and posture. |
| Visceral / smooth | Inner walls of hollow visceral organs; non-striated and smooth. | Involuntary; moves food in digestive tract and gametes in genital tract. |
| Cardiac | Heart; branching cells and striated appearance. | Involuntary; nervous system does not directly control activity. |
Skeletal muscle fibre and sarcomere
A skeletal muscle contains fascicles held by fascia; each fascicle contains muscle fibres. A fibre has sarcolemma, sarcoplasm with many nuclei (syncytium), calcium-storing sarcoplasmic reticulum, and parallel myofibrils.
| Region / component | NCERT description |
|---|---|
| I band | Light isotropic band containing thin actin filaments; centrally bisected by Z line. |
| A band | Dark anisotropic band containing thick myosin filaments; M line holds them at centre. |
| Sarcomere | Segment between two successive Z lines; functional unit of contraction. |
| H zone | Central thick-filament region not overlapped by thin filaments in resting state. |
| Myofilaments | Actin is thin; myosin is thick. Their alternating arrangement causes striations. |
Contractile proteins: actin and myosin
| Feature | Actin thin filament | Myosin thick filament |
|---|---|---|
| Basic organisation | Two helically wound F-actins; each F-actin is a polymer of G-actin monomers. | Polymer of many meromyosins. |
| Associated proteins | Tropomyosin runs along F-actin. Troponin occurs at intervals; in resting state a subunit masks myosin-binding sites. | Each meromyosin has head + short arm (heavy meromyosin/HMM) and tail (light meromyosin/LMM). |
| Functional site | Exposed active sites bind myosin after Ca2+-troponin interaction. | Globular head is ATPase; has ATP-binding and actin-binding sites, and projects as cross arm. |
17.2.2 Sliding-filament theory of contraction
- CNS signal travels through a motor neuron. A motor neuron plus the muscle fibres it supplies is a motor unit; their junction is neuromuscular junction / motor-end plate.
- Acetylcholine release generates an action potential on sarcolemma, causing Ca2+ release from sarcoplasmic reticulum.
- Ca2+ binds troponin, removing the masking of actin sites. ATP-powered myosin head binds actin, forming a cross bridge.
- Cross bridges pull thin filaments towards centre of A band; Z lines move inward and sarcomere shortens.
- Myosin releases ADP and Pi; new ATP breaks the bridge and further ATP hydrolysis resets the head. Repeated cycles produce sliding.
- Ca2+ returns to sarcoplasmic cisternae; actin sites are masked and muscle relaxes.
During contraction I bands and H zone decrease, while the A band retains its length.
Muscle fatigue and red versus white fibres
Repeated muscle activation can cause lactic-acid accumulation from anaerobic glycogen breakdown, producing fatigue.
| Feature | Red fibres | White fibres |
|---|---|---|
| Colour / myoglobin | Reddish due to high oxygen-storing myoglobin. | Pale or whitish due to very little myoglobin. |
| Mitochondria | Many mitochondria. | Few mitochondria. |
| Energy pathway | Aerobic; uses abundant stored oxygen for ATP production. | Mainly anaerobic; sarcoplasmic reticulum is comparatively abundant. |
17.3 Skeletal system: axial and appendicular divisions
Human skeletal system contains 206 bones plus cartilages. Bone has hard calcium-salt matrix; cartilage has a slightly pliable chondroitin-salt matrix.
| Division | Major components and NCERT facts |
|---|---|
| Axial skeleton (80 bones) | Skull, vertebral column, sternum and ribs. Skull: 22 bones (8 cranial + 14 facial), hyoid, and 3 ear ossicles per middle ear. Vertebral column: 26 units - cervical 7, thoracic 12, lumbar 5, sacral 1 fused and coccygeal 1 fused. |
| Rib cage | 12 pairs. First 7 true ribs; 8th-10th vertebrochondral / false ribs; 11th-12th floating ribs. Ribs are bicephalic. |
| Appendicular skeleton | Limb bones with girdles; each limb has 30 bones. Hand: humerus, radius, ulna, 8 carpals, 5 metacarpals, 14 phalanges. Leg: femur, tibia, fibula, 7 tarsals, 5 metatarsals, 14 phalanges and patella. |
| Girdles | Pectoral half: clavicle + scapula; glenoid cavity receives humerus. Pelvic girdle: two coxal bones, each from fused ilium, ischium and pubis; acetabulum receives femur. |
17.4 Joints
Joints are contacts between bones, or bone and cartilage. Muscle force acts through joints as a fulcrum.
| Joint type | Movement and example |
|---|---|
| Fibrous | No movement; dense connective tissue sutures between flat skull bones form cranium. |
| Cartilaginous | Limited movement; adjacent vertebrae are joined by cartilage. |
| Synovial | Fluid-filled cavity allows considerable movement. Ball-and-socket: shoulder; hinge: knee; pivot: atlas-axis; gliding: carpals; saddle: thumb carpal-metacarpal. |
17.5 Disorders of muscular and skeletal system
| Disorder | Description |
|---|---|
| Myasthenia gravis | Autoimmune disorder at neuromuscular junction; fatigue, weakening and paralysis of skeletal muscles. |
| Muscular dystrophy | Progressive skeletal-muscle degeneration, mostly due to genetic disorder. |
| Tetany | Rapid muscle spasms / wild contractions due to low Ca2+ in body fluid. |
| Arthritis | Inflammation of joints. |
| Osteoporosis | Age-related reduced bone mass and higher fracture risk; lower estrogen is a common cause. |
| Gout | Joint inflammation due to uric-acid crystal accumulation. |
NCERT revision prompts
- Differentiate movement from locomotion and name the three human cell-movement types.
- Compare skeletal, visceral and cardiac muscle.
- Label I band, A band, H zone, Z line and M line in a sarcomere.
- Compare actin and myosin proteins.
- Explain the sliding-filament theory and changes in bands during contraction.
- Differentiate red and white fibres.
- Compare axial and appendicular skeleton; account for rib types and vertebral regions.
- Compare fibrous, cartilaginous and synovial joints with examples.
- State causes or features of the listed muscular and skeletal disorders.