Ch.50 Structure and Function of the Musculoskeletal System
Musculoskeletal System Overview
- Components:
- Bone
- Joints
- Cartilage
- Tendons and Ligaments
- Skeletal Muscle
Bone Structure and Function
- Primary Purposes of the Skeletal System:
- Protects internal organs
- Provides bony attachments for muscles and ligaments
- Acts as rigid levers for functional movement
- Stores minerals and marrow for blood cell production
- Bone Characteristics:
- Highly vascular and metabolically active throughout life
- Composition:
- Organic matrix (collagen & cellular components such as osteoblasts, osteocytes, osteoclasts)
- Minerals (calcium, phosphorus)
- Water
- Types of Bone:
- Cortical Bone: Dense and compact, resistant to compression
- Cancellous Bone: Lighter, adapts to stress and external loads
- Periosteum:
- Fibrous membrane covering bones, highly vascular
- Does not cover ends of bones
- Functional Properties:
- Can alter shape and density based on mechanical demands
- Lack of stress can lead to demineralization
Response to Injury, Stress, and Aging
- Wolff's Law:
- Bone is strengthened where needed and resorbed when not
- Imbalance of osteoclast and osteoblast activity can decrease bone mass
- Aging and certain diseases can lead to reduced bone strength
Fracture Healing Process
- Five stages of healing:
- Hematoma Formation (1 to 3 days)
- Fibrocartilage Formation (3 days to 2 weeks)
- Callus Formation (2 to 6 weeks)
- Ossification (3 weeks to 6 months)
- Consolidation/Remodeling (6 weeks to 1 year)
Joints and Their Functions
- Definition: Articulation point between bones, allowing for movement
- Types of Joints:
- Synarthroses (immovable):
- Fibrous (e.g., sutures in skull)
- Cartilaginous (e.g., symphysis)
- Diarthroses (movable): Synovial joints
- Structure of Synovial Joints:
- Joint capsule, synovial membrane, synovial fluid, hyaline cartilage
- Types of movements:
- Uniaxial (hinge, pivot)
- Biaxial (condyloid, saddle)
- Triaxial (ball-and-socket)
Articular Cartilage
- Function:
- Distributes loads, reduces friction, and allows movement
- Composition:
- >70% water, collagen fibers, proteoglycans
- Properties:
- Tolerates compression, needs lubrication to prevent breakdown
Tendons and Ligaments
- Roles:
- Tendons attach muscles to bones to facilitate movement
- Ligaments connect bone to bone for stability
- Composition:
- Dense connective tissue with aligned collagen fibers
Skeletal Muscle
- Importance:
- Comprises 40% of body weight, key for movement and protection
- Structure:
- Made of muscle fibers grouped into bundles (fasciculi)
- Surrounded by connective tissue: endomysium, perimysium, epimysium
- Mechanics of Contraction:
- Sliding filament theory: Myosin and actin interplay for muscle contraction, ATP and calcium are essential
- Response to Activity:
- Exercise enhances muscle strength, while lack of use leads to atrophy and reduced function
Summary
- The musculoskeletal system is vital for movement, stability, and protection of the body, comprising bones, joints, cartilage, tendons, ligaments, and skeletal muscles, all working collaboratively to enable diverse functional capacities.
