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Musculoskeletal System Notes

Components of the Musculoskeletal System

  • Components: Bones, cartilage, ligaments, tendons, joints, skeletal muscle.

Primary Purposes of the Skeletal System

  1. Protection: Safeguards internal organs.
  2. Attachment: Provides bony connections for muscles and ligaments.
  3. Movement: Acts as rigid levers for bodily movements.
  4. Storage: Holds minerals and bone marrow for blood cell formation.

Composition of Bone

  • Collagen & Organic Matrix: 30-40%
  • Mineral Content: 60-70% (primarily hydroxyapatite)
  • Cellular Components: 1-2% including:
    • Osteoblasts: Bone-forming cells.
    • Osteocytes: Mature bone cells maintaining bone matrix.
    • Osteoclasts: Responsible for bone resorption.
    • Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts.

Types of Bone

  • Dense/Compact Bone:

    • Location: Outer layer (cortical bone).
    • Structure: Resistant to compression, dense.

  • Trabecular/Spongy Bone:

    • Type: Cancellous, lighter, laid down in response to stress.
    • Location: Inner layers of flat bones such as the skull, ribs, pelvis.

Periosteum

  • Description: Outermost layer of bone, fibrous, covers all bones.
  • Layers:
    • Fibrous Layer: Dense irregular connective tissue.
    • Cellular Layer: Contains osteogenic cells (stem cells).
  • Function: Attachment point for tendons and ligaments.

Functional Properties of Bone

  • Capable of altering shape and density in response to mechanical demands.
  • Immobility leads to bone demineralization.

Wolff’s Law

  • Bone is deposited where stresses are applied and resorbed where there are none.
  • Without mechanical load, osteoclast activity increases leading to decreased bone mass.

Bone Fracture Healing

  • Stages of Healing:
    1. Hematoma Formation (1-3 days)
    2. Fibrocartilage Formation (3 days-2 weeks)
    3. Callus Formation (3 days-2 weeks)
    4. Ossification (3 weeks-6 months)
    5. Consolidation/Remodeling (6 weeks-1 year)
  • Clinical Healing: Assessed by reduced pain, normal movement, and confirmed imaging.

Articulation (Joints)

  • Definition: Where two or more bones meet.
  • Categories:
    1. Synovial Joints: Free-moving, include diarthroses.
    2. Non-synovial Joints: Fibrous and cartilaginous.

Types of Synovial Joints

  • Uniaxial Joints:

    • Hinge Joint: Allows motion in one direction (e.g., elbow).
    • Pivot Joint: Allows rotation around an axis (e.g., atlantoaxial joint).

  • Biaxial Joints:

    • Condyloid Joint: Allows movement in two planes (e.g., wrist).
    • Saddle Joint: Allows movement in various directions (e.g., thumb).

  • Triaxial Joints:

    • Permits movement around three axes (e.g., ball-and-socket joint in shoulder).

Articular Cartilage

  • Location: Covers bone ends in synovial joints.
  • Function: Helps withstand stress from bone movement.
  • Composition: 70% water, inorganic salts, collagen fibers, and chondrocytes.

Tendons and Ligaments

  • Function: Provide joint stability without direct movement.
  • Composition: Dense connective tissue with parallel collagen fibers, few cells, and high extracellular matrix.

Skeletal Muscle

  • Role: Enables movement of bones at joints.
  • Composition: Made of muscle fibers encased in sarcolemma, grouped into fasciculi, surrounded by connective tissue (epimysium).

Muscle Contraction Mechanism

  • Key Proteins:
    • Myosin: Thick filament.
    • Actin: Thin filament, covered by tropomyosin when calcium is absent.
    • Calcium: Triggers uncovering of actin for contraction.
  • Imbalances: Too little calcium prevents contraction, while too much can disrupt muscle function.

Osteomyelitis

  • Definition: Severe bone infection, often due to Staphylococcus.
  • Ways to reach bone: Through blood, adjacent soft tissue, direct introduction.
  • Symptoms: High fever and localized pain in children; malaise and anorexia in adults.

Scoliosis

  • Definition: Lateral curvature of the spine.
  • Types:
    1. Nonstructural: Temporary, resolves when lying down.
    2. Structural: Permanent, associated with vertebral deformities.
  • Treatment: Bracing, exercise, surgery.

Osteoporosis

  • Definition: Metabolic bone disease characterized by decreased bone density.
  • Risk Factors: Age, gender (more common in postmenopausal women), family history.
  • Symptoms: Fractures, back pain, changes in posture.
  • Treatment: Supplements, exercise, medications (e.g., bisphosphonates).

Muscular Dystrophy

  • Definition: Genetically determined muscle disorders, leading to progressive weakness.
  • Duchenne Muscular Dystrophy: Caused by a deficiency in dystrophin, leads to muscle necrosis.
  • Symptoms: Muscle wasting, difficulty walking, eventual need for wheelchair use.
  • Treatment: Education, corticosteroids, supportive therapies.

Myasthenia Gravis

  • Definition: Autoimmune disorder affecting voluntary muscle function.
  • Symptoms: Muscle weakness increasing with use, improving with rest.
  • Treatment: Anticholinesterase inhibitors, immunosuppressants.

Rheumatic Disorders

  • Definition: Common musculoskeletal disorders include arthritis.
  • Osteoarthritis: Non-inflammatory, wear and tear of joints, treated with pain relief and joint protection.
  • Rheumatoid Arthritis: Autoimmune, inflammation of joints affecting multiple areas; requires disease-modifying treatments.