Chapter at a glance
- All locomotions are movements but all movements are not locomotions; voluntary movements causing change of place are called locomotion.
- Human body cells exhibit three types of movement: amoeboid, ciliary and muscular.
- Muscles are classified by location into skeletal (striated, voluntary), visceral/smooth (non-striated, involuntary) and cardiac (striated, involuntary).
- Each skeletal muscle fibre (syncytium) contains parallel myofibrils showing alternate A (anisotropic, myosin) and I (isotropic, actin) bands; sarcomere is the functional unit between two successive Z-lines.
- Sliding filament theory explains contraction: thin actin filaments slide over thick myosin filaments with cross-bridge formation powered by ATP hydrolysis and Ca²⁺ release.
- Axial skeleton (80 bones) comprises skull, vertebral column, sternum and ribs; appendicular skeleton comprises limb bones and girdles (total 206 bones).
- Joints are classified as fibrous (immovable), cartilaginous (limited movement) and synovial (considerable movement); examples include ball-and-socket, hinge, pivot, gliding and saddle joints.
- Disorders include myasthenia gravis, muscular dystrophy, tetany, arthritis, osteoporosis and gout.
Definitions and laws
- Locomotion: Voluntary movements which result in a change of place or location.
- Amoeboid movement: Effected by pseudopodia formed by streaming of protoplasm (as in macrophages and leucocytes); involves cytoskeletal microfilaments.
- Ciliary movement: Coordinated movement of cilia lining internal tubular organs (e.g., trachea, female reproductive tract).
- Sarcomere: Portion of the myofibril between two successive Z-lines; functional unit of contraction.
- Sliding filament theory: Contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments.
- Red fibres: Muscles with high myoglobin content and numerous mitochondria; aerobic.
- White fibres: Muscles with less myoglobin, few mitochondria and high sarcoplasmic reticulum; anaerobic.
- Axial skeleton: Comprises 80 bones distributed along the main axis (skull, vertebral column, sternum, ribs).
- Appendicular skeleton: Bones of the limbs along with their girdles.
Important diagrams and activities
- Figure 17.1: Diagrammatic cross-sectional view of muscle showing fascicles and muscle fibres.
- Figure 17.2: Anatomy of muscle fibre showing sarcomere with A, I, H, Z and M lines.
- Figure 17.3: Structure of actin (thin) filament (F-actin, tropomyosin, troponin) and myosin monomer (HMM head with cross-arm, LMM tail).
- Figure 17.4: Stages of cross-bridge formation, rotation of myosin head and breakage.
- Figure 17.5: Sliding-filament theory showing shortening of I-band and H-zone during contraction.
- Figure 17.6: Human skull (cranial and facial bones, hyoid, ear ossicles, occipital condyles).
- Figure 17.7: Vertebral column (atlas, cervical, thoracic, lumbar, sacral, coccygeal regions).
- Figure 17.8: Rib cage (true ribs, vertebrochondral ribs, floating ribs, sternum).
- Figure 17.9: Pectoral girdle (clavicle, scapula, glenoid cavity) and upper limb bones.
- Figure 17.10: Pelvic girdle (coxal bones, acetabulum) and lower limb bones (including patella).
Common misconceptions and exam pitfalls
- Confusing “all movements are locomotions” (text states the opposite).
- Mixing red fibres (aerobic, myoglobin-rich) with white fibres (anaerobic) or assuming cardiac muscle is voluntary.
- Incorrect rib count or classification (true vs. vertebrochondral vs. floating); stating 11 pairs instead of 12.
- Forgetting that H-zone contains only thick filaments and disappears during contraction; or that A-band length remains constant.
- Listing wrong number of bones in limbs/girdles or misidentifying joint types (e.g., atlas-axis as hinge instead of pivot).
- Omitting that troponin masks myosin-binding sites on actin in resting state.
Formula sheet
No numerical formulas or equations are given in the chapter.