Study Notes on Joints for BIOL 213

Definition: Articular cartilage is a smooth, resilient tissue that covers the surface of bones at joints (epiphyses) to facilitate smooth movement.
Function: Helps smoothly connect bones, reducing friction, and preventing bone grinding during movement.

Joints are the locations where bones articulate (join together).
Types of Joints:
- Fibrous Joints: Made entirely of fibrous connective tissue.
- Cartilaginous Joints: Joined by hyaline cartilage and/or fibrocartilage.
- Synovial Joints: Bones connected indirectly through a fluid-filled cavity (most common type).

Synarthroses: Joints that allow little or no motion.
- Example: Sutures of the skull, which connect skull bones with minimal movement to protect the brain.
Amphiarthroses: Joints that allow limited movement.
- Example: Intervertebral discs, which provide support yet allow some mobility.
Diarthroses: Joints with a free and fluid range of motion, encompassing all synovial joints.
- Types of Diarthroses:
- Uniaxial Joints: Motion along one axis (e.g., elbow).
- Biaxial Joints: Motion along two axes (e.g., metatarsal knuckles).
- Multiaxial Joints: Motion along all three axes (e.g., ball-and-socket joints like hip and shoulder).

Definition: Joints made of fibrous connective tissue.
- Types:
- Sutures: Connect skull bones, convoluted for stress resilience.
  - Fontanelles in infants allow flexibility; close as ossification occurs (synostosis).
- Syndesmoses: Parallel bones connected by fibrous connective tissue, permitting varying degrees of motion and muscle attachment.
- Gomphosis: A specialized fibrous joint (tooth and socket).

Definition: Joints connected by cartilage.
- Types:
- Synchondroses: Joined by hyaline cartilage.
  - Example: Epiphyseal plate connecting diaphysis and epiphysis of long bones (ossifies into epiphyseal line).
- Symphyses: Joined by fibrocartilage, which is stronger and does not ossify.
  - Example: Intervertebral discs, pubic symphysis, and manubriosternal joint.

Definition: Joints that form an articular capsule with an outer layer of articular cartilage.
- Components:
- Synovial Membrane: Secretes synovial fluid, lubricating the joint.
- Ligaments: Connect bone to bone, provide stability.
  - Types: Extrinsic, intrinsic, and intracapsular depending on their position.
- Bursae: Pads of connective tissue cushioning between bones and soft tissues.
  - Types: Subcutaneous, submuscular, subtendinous based on location.
Types of Synovial Joints: Many types exist, each allowing different motions based on their mechanical connections.

As individuals age, connective tissue, including articular cartilage, deteriorates leading to conditions such as:
- Osteoarthritis: The body increases production of synovial fluid to reduce wear, which can lead to joint pain and stiffness.
- Other Arthritis Forms:
- Gout: Uric acid crystal accumulation due to inadequate kidney filtration.
- Rheumatoid Arthritis: Autoimmune response leading to inflammation of the synovial membrane, damaging articular cartilage.

Embryologic Development: Joints develop from mesenchyme associated with bones.
- Intramembranous Ossification: Forms cranial bones, with mesenchyme differentiating into fibrous tissue for fontanelles.
- Endochondral Ossification: Forms synovial joints and articular cartilage without ossification.

Flexion: Contracts muscles, moving body parts closer together; opposite is extension (returns to extended state).
Hyperflexion/Hyperextension: Movement beyond normal limits.
Abduction: Movement away from midline; Adduction: Movement towards midline.
Circumduction: Circular movement of a limb.
Rotation: Turning around a point; may be medial or lateral.
Supination: Forearm palm facing up; Pronation: Palm facing down.
Ankle Movements:
- Dorsiflexion: Foot rotating up.
- Plantar Flexion: Foot rotating down.
Inversion/Eversion: Sole rotation inward/outward for balance.
Protraction/Retraction: Forward/backward movement (e.g., mandible).
Elevation/Depression: Raising/lowering body parts; Excursion: Moving the mandible laterally/recursively.
Opposition: Thumb and finger movement towards each other; Reposition: Returning to the anatomical position.

How do we classify joints? What types exist and where are they found?
How do fibrous, cartilaginous, and synovial joints function structurally to facilitate movement?
What developmental processes affect joint formation? How do joints change with age?
What movements can joints perform, and which body parts are involved?