The Skeletal System: Joints (Articulations) – Classification and Structure

The Skeletal System: Joints (Articulations)

Introduction to Joints

Joints, also known as articulations, are anatomical structures where two or more bones meet. They play a crucial role in providing movement and stability to the skeletal system. Joints are classified based on their functional range of motion.

• Synarthrosis: Immovable joints

• Amphiarthrosis: Slightly movable joints

• Diarthrosis: Freely movable joints

Joint Classification

Synarthrosis (Immovable Joints)

Synarthroses are joints that do not permit movement. They are primarily found in locations where bones must be held tightly together for protection or support.

• Sutures: Joints found only in the skull, where bones are interlocked together via sutural ligaments.

• Example: The cranial sutures, such as the coronal, sagittal, and lambdoid sutures, which fuse the bones of the skull.

Amphiarthroses (Slightly Movable Joints)

Amphiarthroses allow limited movement and are typically connected by cartilage or ligaments. These joints provide both stability and flexibility.

• Symphysis: Bones are separated by a wedge or pad of cartilage.

• Example: The pubic symphysis, located between the pubic bones of the two coxal bones.

Diarthroses (Freely Movable Synovial Joints)

Diarthroses, also known as synovial joints, are the most common type of joint in the body. They are typically found at the ends of long bones and allow a wide range of movements.

• Synovial joints: Characterized by the presence of a joint cavity filled with synovial fluid, articular cartilage, and supporting ligaments.

• Example: The knee, shoulder, and elbow joints.

Summary Table: Joint Classification

Joint Type	Mobility	Main Example	Structural Features
Synarthrosis	Immovable	Sutures of the skull	Bones interlocked by sutural ligaments
Amphiarthrosis	Slightly movable	Pubic symphysis	Bones separated by cartilage (symphysis)
Diarthrosis (Synovial)	Freely movable	Knee, shoulder	Joint cavity, synovial fluid, articular cartilage

Key Terms and Definitions

• Articulation: The site where two bones meet.

• Suture: An immovable joint found only in the skull.

• Symphysis: A joint where bones are separated by a pad of cartilage.

• Synovial Joint: A freely movable joint characterized by a synovial cavity.

Applications and Importance

• Understanding joint classification is essential for diagnosing joint disorders and injuries.

• Synovial joints are critical for complex movements such as walking, running, and grasping.

• Immovable joints protect vital organs, such as the brain within the skull.