Musculoskeletal System: Joints and Muscles

Chapter 9: Joints and Movements

1. Joint Classifications

• Structural Types:

  • Fibrous: No cavity; mostly immobile. Examples include:
  • Sutures
  • Gomphoses
  • Syndesmoses
  • Cartilaginous: No cavity; slight movement. Examples include:
  • Synchondroses
  • Symphyses
  • Synovial: Cavity present; freely movable. Types include:
  • Hinge
  • Pivot
  • Saddle
  • Ball-and-socket
  • Condyloid
  • Gliding

• Functional Types:

  • Synarthrosis: Immovable (e.g., skull sutures)
  • Amphiarthrosis: Slightly movable (e.g., pubic symphysis)
  • Diarthrosis: Freely movable (e.g., shoulder, knee)

2. Synovial Joint Structures

• Articular cartilage: Covers bone ends to reduce friction
• Synovial fluid: Lubricates and nourishes joint
• Joint capsule: Encloses the synovial cavity
• Accessory structures:
  • Bursae (fluid-filled sacs)
  • Menisci (cartilage pads)
  • Tendons and ligaments

3. Joint Movements

• Angular Movements:
  • Flexion
  • Extension
  • Hyperextension
  • Abduction
  • Adduction
• Rotational Movements:
  • Medial
  • Lateral
  • Pronation
  • Supination
• Special Movements:
  • Inversion/Eversion
  • Protraction/Retration
  • Elevation/Depression
  • Opposition (e.g., thumb to fingertips)

Chapter 10: Muscle Tissue and Physiology

1. Muscle Types

• Skeletal Muscle:
  • Striated, voluntary, multinucleated
• Cardiac Muscle:
  • Striated, involuntary, branched, intercalated discs
• Smooth Muscle:
  • Non-striated, involuntary, spindle-shaped

2. Muscle Properties

• Contractility: Ability to shorten with force
• Excitability: Ability to respond to stimuli
• Extensibility: Ability to stretch beyond resting length
• Elasticity: Ability to recoil to original length

3. Skeletal Muscle Structure

• Epimysium: Covers the entire muscle
• Perimysium: Covers fascicles (bundles of muscle fibers)
• Endomysium: Covers individual myofibers (muscle fibers)
• Myofibrils: Composed of repeating units called sarcomeres

4. Sarcomere Components

• Z-discs: Define the boundaries of each sarcomere
• I band: Actin only
• A band: Overlap of actin and myosin
• H zone: Myosin only
• M line: Center of the sarcomere

5. Sliding Filament Model

1. Action potential travels down T-tubules
2. Ca$^{2+}$ released from sarcoplasmic reticulum
3. Ca$^{2+}$ binds to troponin → tropomyosin shifts
4. Myosin binds to actin → power stroke (ATP required)
5. Muscle shortens (sarcomere contracts)

6. Muscle Fiber Types

• Slow Oxidative (Type I): Endurance; high in myoglobin and mitochondria
• Fast Glycolytic (Type IIx): Short bursts of energy; fatigues quickly
• Fast Oxidative-Glycolytic (Type IIa): Intermediate characteristics

7. Motor Unit

• Definition: 1 motor neuron + all innervated fibers
• Control Types:
  • Gross control: Large units (e.g., thigh muscles)
  • Fine control: Small units (e.g., eye muscles)

Chapter 11: Gross Muscle Anatomy

1. Muscle Naming Conventions

• Based on various factors:
  • Location
  • Size (e.g., brevis, maximus)
  • Shape
  • Action
  • Fiber direction
  • Number of origins

2. Attachments

• Origin: Less movable attachment point
• Insertion: More movable attachment point
• Belly: Central, thick region of the muscle

3. Muscle Actions

• Agonist (Prime Mover): Primary muscle responsible for movement
• Antagonist: Opposes the agonist
• Synergist: Assists the agonist
• Fixator: Stabilizes the origin for efficient movement

4. Key Muscle Groups

• Quadriceps: Include rectus femoris, vastus lateralis, vastus medialis, vastus intermedius
• Hamstrings: Include biceps femoris, semitendinosus, semimembranosus
• Rotator Cuff Muscles: Include supraspinatus, infraspinatus, subscapularis, teres minor
• Abdominals: Include rectus abdominis (commonly known as the 6-pack)
• Back Extension Muscles: Include the erector spinae group

High-Yield Exam Concepts

• Familiarize with joint types and examples (e.g., suture = fibrous)
• Understand structures of synovial joints and movement types
• Review matching sections:
  • Sarcomere structure
  • NMJ (Neuromuscular Junction) steps
  • Muscle groups
• Muscle fiber types and properties
• Sequence of action potentials: neuron → NMJ → muscle contraction
• Effects of missing acetylcholinesterase = spastic paralysis
• Changes in sarcomere during contraction:
  • A band remains constant
  • I band and H zone shorten
• Motor unit recruitment: More activation = stronger contraction
• ATP sources: Aerobic = most efficient
• Definitions of isotonic vs. isometric contractions.