Study Notes: Chapter 8 – Joints (Articulations) in Human Anatomy & Physiology

Chapter 8: Joints (Articulations)

8.1 Classification of Joints

Joints, or articulations, are the sites where two or more bones meet. They provide the skeleton with mobility and hold it together. Joints are classified both structurally and functionally.

• Structural Classification:

  • Fibrous joints: Bones are joined by dense fibrous connective tissue; no joint cavity is present.

  • Cartilaginous joints: Bones are united by cartilage; no joint cavity is present.

  • Synovial joints: Bones are separated by a fluid-filled joint cavity.

• Functional Classification:

  • Synarthroses: Immovable joints

  • Amphiarthroses: Slightly movable joints

  • Diarthroses: Freely movable joints

Example: The knee is a synovial joint and a diarthrosis (freely movable).

8.2 Fibrous Joints

Fibrous joints are connected by dense fibrous tissue and lack a joint cavity. They are mostly immovable.

• Sutures: Found only in the skull; immovable.

• Syndesmoses: Bones connected by ligaments; allow slight movement. Example: distal tibiofibular joint

• Gomphoses: Peg-in-socket joints; Example: teeth in alveolar sockets

8.3 Cartilaginous Joints

Cartilaginous joints unite bones by cartilage and do not have a joint cavity. They permit little to no movement.

• Synchondroses: Bones united by hyaline cartilage; immovable. Example: epiphyseal plates, rib-sternum junctions

• Symphyses: Bones united by fibrocartilage; slightly movable. Example: pubic symphysis, intervertebral discs

8.4 Synovial Joints

Synovial joints are the most movable type of joint and have a fluid-filled cavity. Most joints in the limbs are synovial.

• Key Structures:

  • Articular cartilage: Hyaline cartilage covering bone ends

  • Joint cavity: Space containing synovial fluid

  • Articular capsule: Encloses the joint cavity; consists of fibrous and synovial layers

  • Ligaments: Reinforce the joint

• Synovial Fluid: Secreted by the synovial membrane; lubricates and nourishes articular cartilage

• Types of Cartilage: Articular cartilage is hyaline; menisci are fibrocartilage

Structures of a Generalized Synovial Joint

• A: Ligament

• B: Joint Cavity

• C: Articular Cartilage

• D: Articular Capsule

8.4c Stabilization of Synovial Joints

Three natural factors stabilize synovial joints:

• Articular surfaces

• Ligaments

• Muscle tone (most important)

8.4d Body Movements at Synovial Joints

Body movements are classified by the direction and plane of movement.

• Gliding: Flat bone surfaces slide past each other

• Angular Movements: Change the angle between bones

  • Flexion: Decreases the angle

  • Extension: Increases the angle

  • Abduction: Moves limb away from midline

  • Adduction: Moves limb toward midline

  • Circumduction: Circular movement

• Rotation: Bone turns around its own axis

• Special Movements:

  • Protraction: Moves a body part forward

  • Retraction: Moves a body part backward

  • Elevation: Lifts a body part superiorly

  • Depression: Moves a body part inferiorly

  • Opposition: Moves the thumb to touch other fingers

  • Supination/Pronation: Rotates the forearm

  • Dorsiflexion/Plantar flexion: Moves the foot upward/downward

  • Inversion/Eversion: Turns the sole of the foot medially/laterally

8.4e Types of Synovial Joints and Examples

Synovial joints are classified by the shape of their articular surfaces and the movements they allow.

Type of joint	Movement allowed (nonaxial, uniaxial, biaxial, or multiaxial)	Example in the body
Condyle	Biaxial	Knuckles and wrist
Pivot	Uniaxial	Radius and ulna
Plane	Nonaxial	Intercarpal joints, intertarsal joints, joints between vertebral articular surfaces
Ball and socket	Multiaxial	Shoulder and hip
Saddle	Biaxial	Carpometacarpal joints of the thumbs
Hinge	Uniaxial	Elbow and fingers

Joint Descriptions and Major Joints

Major joints can be compared by their structure and function:

Description	Temporomandibular Joint	Shoulder Joint	Elbow Joint	Knee Joint	Hip Joint
Largest and most complex joint				X
Ball-and-socket joint formed by the glenoid cavity of the scapula and the head of the humerus		X
Hinge joint in which ulna (and radius) articulates with humerus			X
Has stabilizing rotator cuff muscles		X
Deep articular surfaces; capsule heavily reinforced by ligaments					X
Highly adapted for weight bearing					X
Articular surfaces are most important factor for ensuring joint stability				X
Most freely movable joint in the body		X
Ball-and-socket joint formed by the acetabulum of the hip bone and the head of the femur					X
Shallow articular surfaces; capsule is lax and poorly reinforced by ligaments		X

Additional info: These notes expand on the provided questions by including definitions, examples, and context for each joint type and movement, as well as summarizing the major joint types and their characteristics for exam preparation.