The Skeletal System

Functions of the Skeletal System

The skeletal system provides structural support, protection for internal organs, facilitates movement, stores minerals, and houses bone marrow for blood cell production.

• Bone matrix components: The main protein is collagen, and the primary mineral is calcium.

Cells of Bone: Osteocytes, Osteoblasts, Osteoclasts, Osteogenic Cells

• Osteocytes: Mature bone cells that maintain bone tissue.

• Osteoblasts: Cells responsible for bone formation.

• Osteoclasts: Cells that break down bone tissue for remodeling.

• Osteogenic cells: Stem cells that differentiate into osteoblasts.

Bone Membranes

• Periosteum: Outermost membrane with fibrous outer and cellular inner layers.

• Endosteum: Incomplete cellular membrane lining the marrow cavity, central canals, and trabeculae.

Types of Bone Tissue

• Compact bone: Dense structure with osteons (central canals, lamellae, canaliculi, lacunae).

• Spongy bone: Contains trabeculae, lighter and stores bone marrow, withstands stress from multiple directions.

Types of Bones

• Long, flat, sutural, irregular, short, sesamoid: Know their general characteristics and be able to recognize examples.

Structure of Long Bones

• Diaphysis: Shaft, contains medullary cavity.

• Epiphysis: Ends, mostly spongy bone covered by compact bone.

• Metaphysis: Region between diaphysis and epiphysis.

Osteogenesis and Ossification

Osteogenesis is the process of bone formation, always involving calcification.

• Intramembranous ossification: Bone develops directly from mesenchymal tissue (e.g., flat bones of skull).

• Endochondral ossification: Bone develops by replacing hyaline cartilage (e.g., long bones).

Bone Remodeling

• Appositional growth: Bone increases in diameter.

• Remodeling: Involves bone resorption and deposition; regulated by osteoclasts and osteoblasts.

Hormonal Regulation of Bone

• Vitamin D, Vitamin C: Essential for bone health; deficiency leads to bone disorders.

• Growth hormone (GH): Stimulates bone growth; excess leads to gigantism/acromegaly, deficiency to pituitary dwarfism.

• Parathyroid hormone (PTH) and Calcitonin: Regulate calcium levels in blood and bone.

Calcium Homeostasis

• PTH: Released in response to low calcium, increases blood calcium.

• Calcitonin: Released in response to high calcium, decreases blood calcium.

Fractures

• Types: Closed, open, comminuted, greenstick, displaced.

• Steps in fracture repair: Hematoma formation, fibrocartilaginous callus, bony callus, bone remodeling.

Axial and Appendicular Skeleton

• Axial skeleton: Skull, vertebral column, rib cage.

• Appendicular skeleton: Limbs and girdles.

Joints (Articulations)

• Fibrous joints: Sutures, gomphoses, syndesmoses.

• Cartilaginous joints: Synchondroses, symphyses.

• Synovial joints: Most mobile; types include planar, hinge, pivot, condylar, saddle, ball-and-socket.

• Movements: Flexion, extension, abduction, adduction, circumduction, rotation.

The Muscular System

Functions of the Muscular System

Muscles produce movement, maintain posture, stabilize joints, and generate heat.

• Connective tissue membranes: Epimysium, perimysium, endomysium.

Muscle Structure

• Fascicle: Bundle of muscle fibers.

• Muscle fiber types: Parallel, convergent, pennate, bipennate, multipennate, circular.

• Origin and insertion: Origin is the fixed attachment, insertion moves with contraction.

• Levers: First, second, and third class levers in muscle action.

Microscopic Structure of Muscle

• Sarcomere: Functional unit of muscle; contains thick (myosin) and thin (actin, troponin, tropomyosin) filaments.

• Myofibrils: Bundles of protein filaments.

Neural Control/Excitation Phase

• Neuromuscular junction (NMJ): Site where motor neuron stimulates muscle fiber.

• Acetylcholine (ACh): Neurotransmitter released into synaptic cleft.

Excitation-Contraction Coupling

• Steps: Action potential, ACh release, depolarization, calcium release, cross-bridge formation.

• Relaxation: Removal of calcium, breakdown of ACh.

Muscle Contraction Types

• Isotonic: Muscle changes length (concentric and eccentric).

• Isometric: Muscle length remains constant.

Muscle Fiber Types

• Type I (slow-twitch): Fatigue-resistant, aerobic, used for endurance.

• Type II (fast-twitch): Fatigue quickly, anaerobic, used for power and speed.

Energy for Muscle Contraction

• ATP: Main energy source.

• Aerobic respiration: Uses oxygen, produces more ATP.

• Anaerobic fermentation: No oxygen, produces lactic acid.

Cardiac and Smooth Muscle

• Cardiac muscle: Involuntary, striated, found in heart.

• Smooth muscle: Involuntary, non-striated, found in walls of hollow organs.

Summary Table: Types of Joints

Key Equations

• Muscle force:

• ATP production (aerobic):

Additional info:

• Some details on bone and muscle physiology were expanded for clarity and completeness.