Review Sheet Articulations And Body Movements

Articulations, the junctions where bones meet, are fundamental to movement, providing the flexibility and stability required for a vast array of activities. Understanding the different types of articulations and the corresponding body movements they enable is crucial for fields ranging from physical therapy and sports medicine to biomechanics and art. This comprehensive review sheet delves into the classification of articulations, the specific movements they permit, and the muscles that drive these movements.

Classifying Articulations: Structure and Function

Articulations, also known as joints, can be classified based on their structure (the material that binds the bones together) and their function (the range of motion they allow). Structurally, joints are categorized as fibrous, cartilaginous, or synovial. Functionally, they are classified as synarthroses (immovable), amphiarthroses (slightly movable), or diarthroses (freely movable).

Structural Classification

• Fibrous Joints: These joints are connected by dense connective tissue, primarily collagen. They generally allow for little to no movement.

  • Sutures: Found in the skull, sutures are interlocking edges of bone held together by short connective tissue fibers. They are synarthrotic, providing stability and protection for the brain.
  • Syndesmoses: These joints are connected by ligaments, allowing for slight movement. An example is the distal tibiofibular joint in the ankle.
  • Gomphoses: This type of joint exists between a tooth and its socket in the jaw. It's held in place by the periodontal ligament and is considered synarthrotic.

• Cartilaginous Joints: These joints are connected by cartilage, either hyaline cartilage or fibrocartilage. They allow for limited movement.

  • Synchondroses: These joints are connected by hyaline cartilage. An example is the epiphyseal plate in growing bones, which is a temporary joint that ossifies into a synostosis (bony fusion) when growth is complete. Another example is the joint between the first rib and the sternum. These are typically synarthrotic.
  • Symphyses: These joints are connected by fibrocartilage. They provide strength and flexibility. Examples include the intervertebral discs and the pubic symphysis. These are amphiarthrotic.

• Synovial Joints: These are the most common type of joint in the body and allow for the greatest range of motion. They are characterized by a fluid-filled joint cavity.

  • Key Features of Synovial Joints:
    • Articular Cartilage: Hyaline cartilage covers the articulating surfaces of the bones, providing a smooth, low-friction surface for movement.
    • Joint Cavity: A space filled with synovial fluid.
    • Synovial Fluid: A viscous fluid that lubricates the joint, reduces friction, and provides nutrients to the articular cartilage.
    • Articular Capsule: A two-layered capsule that encloses the joint cavity. The outer layer is the fibrous capsule, made of dense connective tissue, which provides support and strengthens the joint. The inner layer is the synovial membrane, which produces synovial fluid.
    • Ligaments: Strong bands of connective tissue that connect bones and provide stability to the joint.

Functional Classification

• Synarthrosis: Immovable joints. These joints provide strong connections between bones, protecting internal organs and providing stability. Examples include sutures of the skull.
• Amphiarthrosis: Slightly movable joints. These joints allow for limited movement while providing stability. Examples include the intervertebral discs.
• Diarthrosis: Freely movable joints. These joints allow for a wide range of movements and are characteristic of the limbs. All synovial joints are diarthrotic.

Types of Synovial Joints and Their Movements

Synovial joints are further classified based on the shape of their articulating surfaces, which determines the type of movement they allow.

1. Plane Joints (Gliding Joints): These joints have flat or slightly curved articulating surfaces, allowing for gliding or sliding movements in one plane.

   • Examples: Intercarpal joints (between carpal bones in the wrist), intertarsal joints (between tarsal bones in the ankle), and the vertebrocostal joints (between the ribs and vertebrae).
   • Movements: Gliding, sliding.

2. Hinge Joints: These joints allow for movement in one plane (uniaxial), similar to the hinge of a door.

   • Examples: Elbow joint (between the humerus and ulna), knee joint (between the femur and tibia), and interphalangeal joints (between the phalanges of the fingers and toes).
   • Movements: Flexion (decreasing the angle between bones) and extension (increasing the angle between bones).

3. Pivot Joints: These joints allow for rotation around a single axis (uniaxial).

   • Examples: Atlantoaxial joint (between the atlas and axis vertebrae in the neck, allowing for head rotation) and the radioulnar joint (allowing for pronation and supination of the forearm).
   • Movements: Rotation.

4. Condylar Joints (Ellipsoidal Joints): These joints have an oval-shaped condyle that fits into an elliptical cavity, allowing for movement in two planes (biaxial).

   • Examples: Radiocarpal joint (wrist joint between the radius and carpal bones) and metacarpophalangeal joints (between the metacarpals and phalanges in the hand).
   • Movements: Flexion, extension, abduction (moving away from the midline), adduction (moving towards the midline), and circumduction (a circular movement combining flexion, extension, abduction, and adduction).

5. Saddle Joints: These joints have articulating surfaces that are both concave and convex, resembling a saddle shape. They allow for movement in two planes (biaxial).

   • Example: Carpometacarpal joint of the thumb (between the trapezium and the first metacarpal).
   • Movements: Flexion, extension, abduction, adduction, circumduction, and opposition (touching the thumb to the other fingers).

6. Ball-and-Socket Joints: These joints have a spherical head that fits into a cup-like socket, allowing for movement in multiple planes (multiaxial).

   • Examples: Shoulder joint (between the humerus and scapula) and hip joint (between the femur and acetabulum of the pelvis).
   • Movements: Flexion, extension, abduction, adduction, rotation (medial and lateral), and circumduction.

Fundamental Body Movements

Understanding the specific movements possible at each joint is crucial for analyzing human motion. Here's a breakdown of common body movements:

• Flexion: Decreasing the angle between two bones. Example: Bending the elbow or knee.
• Extension: Increasing the angle between two bones. Example: Straightening the elbow or knee.
• Hyperextension: Extension beyond the normal anatomical position. Example: Bending the head backward.
• Abduction: Moving a limb away from the midline of the body. Example: Raising the arm to the side.
• Adduction: Moving a limb towards the midline of the body. Example: Lowering the arm to the side.
• Rotation: Turning a bone around its longitudinal axis.
  • Medial Rotation (Internal Rotation): Rotating towards the midline. Example: Turning the thigh inward.
  • Lateral Rotation (External Rotation): Rotating away from the midline. Example: Turning the thigh outward.
• Circumduction: A circular movement combining flexion, extension, abduction, and adduction. Example: Moving the arm in a circle.
• Pronation: Rotation of the forearm so that the palm faces posteriorly or inferiorly.
• Supination: Rotation of the forearm so that the palm faces anteriorly or superiorly. Think of holding a bowl of soup.
• Dorsiflexion: Lifting the foot so that the superior surface approaches the shin. Pointing the toes upward.
• Plantar Flexion: Depressing the foot (pointing the toes). Standing on tiptoes.
• Inversion: Turning the sole of the foot medially.
• Eversion: Turning the sole of the foot laterally.
• Protraction: Moving a body part anteriorly in the transverse plane. Example: Thrusting the jaw forward.
• Retraction: Moving a body part posteriorly in the transverse plane. Example: Pulling the jaw backward.
• Elevation: Lifting a body part superiorly. Example: Shrugging the shoulders.
• Depression: Lowering a body part inferiorly. Example: Dropping the shoulders.
• Opposition: Touching the thumb to the tips of the other fingers. Unique to the thumb.
• Reposition: Returning the thumb to its anatomical position after opposition.

Muscles and Their Actions at Joints

Muscles are the primary movers of the skeletal system, acting across joints to produce movement. Understanding the relationship between muscles and joints is crucial for comprehending how the body moves.

• Agonist (Prime Mover): The muscle primarily responsible for a particular movement. Example: Biceps brachii is the agonist for elbow flexion.
• Antagonist: The muscle that opposes or reverses the action of the agonist. Example: Triceps brachii is the antagonist for elbow flexion.
• Synergist: A muscle that assists the agonist in performing a movement. Synergists can stabilize joints or neutralize unwanted movements. Example: Brachialis assists biceps brachii in elbow flexion.
• Fixator: A muscle that stabilizes the origin of the agonist so that it can act more efficiently. Example: Scapular muscles stabilize the scapula during arm movements.

Examples of Muscle Actions at Specific Joints

• Shoulder Joint:
  • Flexion: Anterior deltoid, pectoralis major (clavicular head)
  • Extension: Latissimus dorsi, teres major, posterior deltoid, pectoralis major (sternal head)
  • Abduction: Middle deltoid, supraspinatus
  • Adduction: Pectoralis major, latissimus dorsi, teres major
  • Medial Rotation: Subscapularis, teres major, pectoralis major, latissimus dorsi
  • Lateral Rotation: Infraspinatus, teres minor, posterior deltoid
• Elbow Joint:
  • Flexion: Biceps brachii, brachialis, brachioradialis
  • Extension: Triceps brachii, anconeus
  • Pronation (Forearm): Pronator teres, pronator quadratus
  • Supination (Forearm): Supinator, biceps brachii
• Hip Joint:
  • Flexion: Iliopsoas, rectus femoris, sartorius
  • Extension: Gluteus maximus, hamstrings (biceps femoris, semitendinosus, semimembranosus)
  • Abduction: Gluteus medius, gluteus minimus, tensor fasciae latae
  • Adduction: Adductor magnus, adductor longus, adductor brevis, gracilis
  • Medial Rotation: Gluteus medius (anterior fibers), gluteus minimus, tensor fasciae latae
  • Lateral Rotation: Piriformis, obturator internus, obturator externus, quadratus femoris, gemellus superior, gemellus inferior, gluteus maximus
• Knee Joint:
  • Flexion: Hamstrings (biceps femoris, semitendinosus, semimembranosus), gastrocnemius
  • Extension: Quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius)
• Ankle Joint:
  • Dorsiflexion: Tibialis anterior, extensor hallucis longus, extensor digitorum longus
  • Plantar Flexion: Gastrocnemius, soleus, plantaris
  • Inversion: Tibialis anterior, tibialis posterior
  • Eversion: Peroneus longus, peroneus brevis, peroneus tertius

Factors Affecting Joint Movement

Several factors can influence the range of motion and stability of joints, including:

• Shape of Articulating Surfaces: The configuration of the bony surfaces significantly impacts the type and extent of movement.
• Ligament Arrangement: Ligaments provide stability by connecting bones and resisting excessive or unwanted movements. Their tension and arrangement influence the range of motion.
• Muscle Tone and Strength: Strong, well-toned muscles contribute to joint stability and control. Muscle imbalances can lead to abnormal joint mechanics and increased risk of injury.
• Capsule Flexibility: The articular capsule surrounds the joint and provides additional support. Its flexibility is crucial for allowing a full range of motion.
• Age: Joint flexibility and range of motion tend to decrease with age due to changes in collagen and cartilage.
• Injury: Trauma to joints, such as sprains or dislocations, can damage ligaments, cartilage, or other joint structures, leading to pain, instability, and limited range of motion.
• Genetics: Some individuals are naturally more flexible than others due to genetic variations affecting collagen structure and joint laxity.
• Training and Activity Level: Regular exercise and stretching can improve joint flexibility and range of motion, while inactivity can lead to stiffness and decreased mobility.

Common Joint Injuries and Conditions

Understanding the types of injuries and conditions that can affect joints is essential for healthcare professionals and individuals interested in maintaining musculoskeletal health.

• Sprains: Ligament injuries caused by overstretching or tearing. Common in the ankle, knee, and wrist.
• Strains: Muscle or tendon injuries caused by overstretching or tearing. Common in the back, hamstrings, and calf.
• Dislocations: Displacement of a bone from its normal position in a joint.
• Subluxations: Partial dislocation of a joint.
• Arthritis: A group of conditions characterized by joint inflammation, pain, and stiffness.
  • Osteoarthritis: A degenerative joint disease characterized by the breakdown of articular cartilage.
  • Rheumatoid Arthritis: An autoimmune disease that causes inflammation of the synovial membrane.
  • Gout: A type of arthritis caused by the buildup of uric acid crystals in the joints.
• Bursitis: Inflammation of a bursa, a fluid-filled sac that cushions joints.
• Tendonitis: Inflammation of a tendon.
• Meniscal Tears: Tears in the menisci of the knee, often caused by twisting injuries.
• Labral Tears: Tears in the labrum, a ring of cartilage that stabilizes the shoulder or hip joint.

Clinical Applications

The knowledge of articulations and body movements is applied in numerous clinical settings:

• Physical Therapy: Therapists use their understanding of joint mechanics and muscle actions to design rehabilitation programs for patients with musculoskeletal injuries or conditions.
• Sports Medicine: Physicians and athletic trainers apply this knowledge to prevent and treat sports-related injuries, optimize athletic performance, and develop training programs.
• Occupational Therapy: Therapists use their understanding of movement to help individuals perform daily activities and adapt to physical limitations.
• Orthopedics: Surgeons use their knowledge of joint anatomy and biomechanics to perform joint replacements, arthroscopic procedures, and other surgical interventions.
• Biomechanics Research: Scientists study joint movements and forces to understand human locomotion, develop assistive devices, and improve injury prevention strategies.

Conclusion

A thorough understanding of articulations and body movements is fundamental to appreciating the complexity and functionality of the human musculoskeletal system. By classifying joints based on structure and function, identifying the movements they allow, and recognizing the muscles that drive these movements, one gains valuable insights into how the body moves and interacts with its environment. This knowledge is not only essential for healthcare professionals but also for anyone interested in optimizing physical performance, preventing injuries, and maintaining a healthy, active lifestyle.