Anatomy and Physiology: Joints Study Notes

Anatomy and Physiology: Joints

Introduction

  • Joints are the points of attachment between bones and cartilage.
  • The structure of a joint determines the movement possible.
  • This chapter focuses on:
    • Classification of joints
    • Movements possible at joints

Classification of Joints

Section 10.1 - Learning Objectives 10.1.1–10.1.3
Joints Defined
  • Sites where bones and cartilage connect.
  • Also referred to as articulations or arthroses.
  • Joints can be classified in two main ways:
    • Structural Classification: based on the structure connecting the articulating surfaces of bones.
    • Functional Classification: based on the amount of movement between articulating bones.
Structural Classification of Joints
  • Based on the structure of the articulating surfaces:
    • Fibrous Joints: connected by fibrous connective tissue.
    • Cartilaginous Joints: connected by cartilage, either hyaline cartilage or fibrocartilage.
    • Synovial Joints: enclosed within a fluid-filled joint cavity; the most common type of joint.
Functional Classification of Joints
  • Based on joint movement:
    • Synarthrosis: little to no movement.
    • Example: sutures of the skull.
    • Amphiarthrosis: slight movement.
    • Examples: pubic symphysis, intervertebral discs.
    • Diarthrosis: significant movement.
    • Further divided into three categories based on axes of motion:
      • Uniaxial: movement in one plane.
      • Example: elbow.
      • Biaxial: movement in two planes.
      • Example: metacarpophalangeal joints.
      • Multiaxial: movement in three or more planes.
      • Example: hip and shoulder joints.
Structural and Functional Relationship
  • The structure of a joint dictates possible movements:
    • Fibrous and Cartilaginous Joints: typically function as synarthroses or amphiarthroses, providing limited movement.
    • Synovial Joints: function as diarthroses, allowing for significant movement.

Knowledge Check Activities

Activity 1
  • Identify the term for a joint that allows no or only slight movement:
    • Possible Answers:
    • Synarthrosis
    • Amphiarthrosis
    • Diarthrosis
    • Synchondrosis
Activity 1 Answer
  • Correct answer: Synarthrosis.
Activity 2 - Think, Pair, Share
  • Discuss how the structure of fibrous, cartilaginous, and synovial joints influences movement.
  • Answer: Connective tissue in fibrous and cartilaginous joints restricts movement, while the synovial cavity provides space allowing greater movement.

Fibrous Joints

Section 10.2 - Learning Objectives 10.2.1–10.2.3
Characteristics of Fibrous Joints
  • No joint cavity present.
  • Bones are held together by dense fibrous connective tissue.
  • Functionally classified as synarthroses, permitting little to no movement.
  • Types of fibrous joints include:
    • Sutures: join the bones of the skull; classified as synarthroses.
    • Syndesmoses: join two parallel bones (like the radius and ulna); classified as amphiarthroses.
    • Gomphoses: anchor teeth to maxilla and mandible; classified as synarthroses.
Think, Pair, Share Activity 2
  • Discuss why adult skull sutures are immovable compared to those in infants.
  • Answer: Adult skull sutures are immovable because the brain size does not increase after infancy, eliminating the need for the cranium to expand, whereas infant sutures need flexibility to accommodate brain growth.

Cartilaginous Joints

Section 10.3 - Learning Objectives 10.3.1–10.3.3
Characteristics of Cartilaginous Joints
  • Bones are joined by either hyaline cartilage or fibrocartilage.
    • Synchondroses: connected by hyaline cartilage.
    • Symphyses: connected by fibrocartilage.
Comparison of Cartilaginous Joints
  • Synchondroses: prominent during early life to allow skeletal growth; classified as synarthroses (e.g., epiphyseal plates, costal cartilage).
  • Symphyses: provide strong attachment but allow limited movement; classified as amphiarthroses (e.g., pubic symphysis, intervertebral discs).
Think, Pair, Share Activity 3
  • Describe structural differences between synchondroses and symphyses.
  • Answer: Synchondroses are connected by hyaline cartilage while symphyses are connected by fibrocartilage.

Synovial Joints

Section 10.4 - Learning Objectives 10.4.1–10.4.3
Characteristics of Synovial Joints
  • Contain a joint cavity enclosed by an articular capsule, which forms the walls of the cavity.
  • Include ligaments that attach bones, a synovial membrane which secretes synovial fluid, lubricating the joint and nourishing cartilage, and articular cartilage (hyaline cartilage at the ends of bones).
  • Classified as diarthroses, allowing significant movement.
Cushioning Structures in Synovial Joints
  • Articular Discs and Menisci: provide shock absorption and smooth movement.
  • Bursa and Tendon Sheaths: prevent friction between bones and tendons.
  • Fat Pads: provide additional cushioning.
Types of Synovial Joints: Functionality and Examples
  1. Pivot Joint: Rounded bone rotates around one axis; uniaxial joint; example: Atlantoaxial joint between C1 and C2 vertebrae.
  2. Hinge Joint: Convex bone end articulates with concave bone end; uniaxial joint; examples: elbow, knee.
  3. Condyloid Joint: Shallow depression articulates with a rounded structure; biaxial joint; example: metacarpophalangeal joints.
  4. Saddle Joint: Both ends shaped like saddles; biaxial joint; examples: carpometacarpal joint of the thumb, sternoclavicular joint.
  5. Plane Joint: Flat surfaces glide past one another; multiaxial joint; examples: intercarpal joints.
  6. Ball-and-Socket Joint: Rounded bone head fits into a bowl-shaped socket; multiaxial joint; examples: hip and shoulder joints.
Examples and Movements of Synovial Joints
  • Pivot Joint: Atlantoaxial joint; permits rotation.
  • Hinge Joint: Elbow joint; allows flexion and extension.
  • Condyloid Joint: Metacarpophalangeal joint; allows bending and straightening.
  • Saddle Joint: Sternoclavicular joint; allows circular movement.
  • Plane Joint: Acromioclavicular joint; bones slide past each other.
  • Ball-and-Socket Joint: Hip joint; provides free movement.

Movements at Synovial Joints

Section 10.5 - Learning Objectives 10.5.1–10.5.2
Types of Movements
  • Flexion: Reduces the angle of a joint from resting position.
  • Extension: Returns joint to resting position.
  • Hyperextension: Increases joint angle beyond 180 degrees.
  • Lateral Flexion: Bends neck or body toward left or right side.
Additional Movements
  • Abduction: Moves a limb away from the midline of the body.
  • Adduction: Moves a limb toward the midline.
  • Circumduction: Circular motion combining flexion, adduction, extension, and abduction.
  • Rotation: Twisting movement; medial rotation moves limbs toward midline, lateral rotation moves limbs away from midline.
  • Supination and Pronation: Movements of the forearm; supination moves palm facing anteriorly, pronation turns palm posteriorly.
  • Dorsiflexion and Plantar Flexion: Movements at the ankle; dorsiflexion lifts the foot toward the leg, plantar flexion points toes down.
  • Inversion and Eversion: Movements of the foot; inversion turns the foot's bottom toward the midline, eversion turns it away.
  • Protraction and Retraction: Protraction moves a body part forward, and retraction pulls it backward.
  • Depression and Elevation: Depression moves downwards, while elevation moves upwards (e.g., shrugging the shoulders).
  • Opposition and Reposition: Opposition brings the thumb and finger together, while reposition returns the thumb to its anatomical position.

Selected Synovial Joints

Section 10.6 - Learning Objectives 10.6.1–10.6.2
Major Synovial Joints
  • Shoulder Joint: Ball-and-socket joint formed by the head of the humerus and glenoid cavity of scapula; allows a large range of motion including flexion, extension, hyperextension, abduction, adduction, medial rotation, lateral rotation, and circumduction.
  • Elbow Joint: Hinge joint formed by the humerus, radius, and ulna; primarily allows flexion and extension.
  • Hip Joint: Ball-and-socket joint formed by the acetabulum and head of the femur; permits several movements similar to the shoulder but with a lesser range of motion.

Knowledge Checks and Discussion Activities

Activity 3
  • Question regarding major hinge joints.
  • Answer: Correct answers are A and B (knee joint and elbow joint).
Activity 5 - Discussion: Complications from Articular Cartilage Loss
  • Loss of articular cartilage leads to increased bone contact within joints, with potential for irritation and pain, commonly referred to as arthritis as it progresses with age.
Summary
  • At the conclusion of this chapter, students should be able to:
    • Discuss and understand the structural classification of joints.
    • Explain the functional classification of joints.
    • Examine the various movements that occur at joints.
    • Identify and describe components of major joints in the body.