Lecture Notes: Synovial Joints

Overview of Synovial Joints

• Definition: Freely movable joints allowing large amounts of smooth movement.
• Structure:
  • Articular Cartilage: Covers ends of articulating bones to prevent wear.
  • Synovial Cavity: Contains synovial fluid and is surrounded by accessory ligaments.
  • Articular Capsule: Composed of a fibrous membrane and a synovial membrane that produces synovial fluid.

Components of Synovial Joints

• Bursa: Sac-like structures filled with synovial fluid to cushion body parts and reduce friction.
• Tendon Sheaths: Tubular bursae wrapped around tendons.

Types of Movements

• Gliding: Movement in flat or cuboidal bones (e.g., carpals in the wrist).
• Extension: Opens a joint (e.g., extending the elbow).
• Flexion: Closes a joint (e.g., bending the elbow).
• Hyperextension: Overextending a joint beyond normal range.
• Abduction: Moving away from the midline.
• Adduction: Moving toward the midline.
• Circumduction: Circular movement, involving multiple types of movements (applies to arms and legs).
• Rotation: Movement around an axis; can be medial or lateral.

Special Movements

• Jaw: Temporal movements include elevation, depression, protraction, and retraction.
• Thumb: Opposition to other fingers.
• Hand: Supination (palm up) and pronation (palm down).
• Foot: Plantar flexion (pointing toes down) and dorsiflexion (pointing toes up).
  • Inversion: Sole faces midline.
  • Eversion: Sole faces away from midline.

Types of Synovial Joints

• Plane Joint: Allows gliding movements (e.g., carpals, tarsals).
• Hinge Joint: Movement in one direction (e.g., elbow).
• Pivot Joint: Rotation around an axis (e.g., between atlas and axis vertebrae).
• Condylar Joint: Allows movement in multiple directions (e.g., wrist joint).
• Saddle Joint: Bone sits like a saddle (e.g., thumb joint).
• Ball and Socket Joint: Most movable (e.g., hip and shoulder), least stable.

Factors Affecting Joint Motion

• Bone Structure: Determines joint type.
• Ligament Strength: Affects stability.
• Muscle Arrangement: Influences tension and joint stability.
• Hormones: e.g., relaxin increases flexibility during childbirth.
• Disuse: Reduces flexibility over time.

Specific Joint Examples

• Temporomandibular Joint: Jaw and temporal bone articulation.
• Atlantoaxial Joint: Between first and second cervical vertebra.
• Glenohumeral Joint: Shoulder joint, ball and socket type.
• Elbow Joint: Hinge joint for flexion and extension.
• Hip Joint: Ball and socket, allows multi-directional movement.
• Knee Joint: Largest joint, complex ligament structure.
• Ankle Joint: Uniaxial hinge joint, allows dorsiflexion and plantar flexion.