Joints

Joints are where two or more bones or a bone and cartilage come together. Many joints allow movement between bones, while some lack movement.

There are 3 different types of joints in the body:

Fibrous joint: Adjacent bones are directly connected by fibrous connective tissue, without a joint cavity.
Cartilaginous joint: Adjacent bones are united by cartilage, which is a tough but flexible type of connective tissue.
Synovial joint: The most common type of joints in the body, allowing for smooth movements between adjacent bones.

Joints can be classified functionally and structurally.

Uniaxial joint: Allows motion in a single plane (around a single axis). Ex: elbow joint.
Biaxial joint: Allows for motion within two planes. Ex: knuckle joint.
Multiaxial joint: Allows for several directions of movement. Ex: shoulder or hip joint.

Focuses on the physical connection between bones (e.g., joined by connective tissue or cartilage) and if a joint cavity is present.

Joints where the bones are united by hyaline cartilage or fibrocartilage. Cartilage is a tough, but flexible type of connective tissue.

Synchondrosis: A cartilaginous joint where bones are connected by hyaline cartilage. These can be temporary or permanent.
Symphysis: A cartilaginous joint where bones are connected by fibrocartilage. This type is much stronger than hyaline cartilage because it contains numerous bundles of collagen fibers. (Highly emphasized as Need to know)

Freely movable joints surrounded by a capsule and containing fluid.

Synovial membrane: The inner lining of the joint capsule, which produces synovial fluid.
Synovial Fluid: Lubricates and nourishes the joints.
Ligament: Connects bones to provide stability.
Bursa: A fluid-filled sac that reduces friction between tissues.
Meniscus: A cartilage pad that cushions and stabilizes the joint.

Pivot: Allows rotation (e.g., turning your head side to side).
Hinge: Allows for flexion and extension (e.g., elbow, knee).
Saddle: Responsible for our opposable thumbs.
Plane (Gliding): Allows for small, precise movements.
Condyloid: Allows for flexion and extension, as well as side-to-side movement (e.g., wrist).
Ball and socket: Multiaxial, allowing for a large range of motion (e.g., shoulder or hip).

Tendons: Strong, flexible bands of connective tissues that attach muscles to bones.
Muscles: Specialized tissues that enable movement and support in the body.

Abduction: Movement in the coronal plane that moves a limb laterally away from the body.
Adduction: Movement in the coronal plane that moves a limb medially toward or across the midline of the body.
Flexion: Movement in the sagittal plane that decreases the angle of a joint, including anterior bending of the vertebral column.
Extension: Movement in the sagittal plane that increases the angle of a joint, including posterior bending of the vertebral column.
Rotation: Movement of a bone around its longitudinal axis.
- Pronation: Rotation of the forearm that moves the palm from an anterior-facing position to a posterior-facing position (e.g., turning the palm down).
- Supination: Rotation of the forearm that moves the palm from a posterior-facing position to an anterior-facing position (e.g., turning the palm up).