Muscle contraction (sliding filament), bone remodeling, skin barrier, thermoregulation.
Musculoskeletal And Integumentary
Sliding-filament model
Huxley-Hanson-Huxley-Niedergerke 1954: muscle contraction is sliding of thin (actin) over thick (myosin) filaments; sarcomere shortens…
Excitation-contraction coupling
Depolarisation → DHPR (L-type Ca²+ channel in T-tubule) → ryanodine receptor → SR Ca²+ release → troponin C → tropomyosin shift →…
Motor unit
One α-motor neuron + all muscle fibres it innervates. Size varies (eye: ~10 fibres; leg: ~1000). Size principle: smaller units recruited…
Bone remodeling
Continuous cycle of osteoclast resorption + osteoblast deposition. Regulated by mechanical load (Wolff's law), PTH, calcitriol, calcitonin,…
Skin barrier (stratum corneum)
Outermost epidermal layer: dead enucleated corneocytes embedded in lipid lamellae (ceramides, cholesterol, free fatty acids). Prevents…
Thermoregulation
Homeostatic control of core body temperature (~37°C) by hypothalamic thermostat. Heat loss: cutaneous vasodilation, sweating. Heat…
Myosin cross-bridge cycle
Myosin-II cross-bridge: ATP-binding detaches, hydrolysis cocks head, actin-binding releases Pi → power stroke. Troponin-tropomyosin…
Muscle fibre types
Type I (slow oxidative, red, fatigue-resistant), Type IIa (fast oxidative-glycolytic), Type IIx (fast glycolytic, white, fatigue-prone).…
Osteoblast-osteoclast coupling
Bone formation (osteoblast, collagen-I + hydroxyapatite) balanced with resorption (osteoclast, H⁺ + cathepsin K). RANKL/OPG regulates…
Connective tissue collagen
Type-I collagen triple helix (Gly-X-Y repeat) crosslinked by lysyl oxidase in bone/tendon. Defects: osteogenesis imperfecta (COL1A1),…