Appendicular Skeleton: Upper Limb

Pectoral Girdle and Upper Limb: Bones, Features, and Surface Anatomy

The appendicular skeleton includes the bones of the limbs and the girdles that attach them to the axial skeleton. The upper limb consists of several regions, each with distinct bones and joints that allow for a wide range of movements.

• Pectoral girdle: Composed of the clavicle and scapula, it attaches the upper limb to the trunk and provides mobility and support.

• Upper limb regions:

  • Arm (brachium): Contains the humerus.

  • Forearm (antebrachium): Contains the radius (lateral) and ulna (medial).

  • Wrist (carpus): Composed of eight carpal bones.

  • Hand (manus): Includes metacarpals and phalanges.

• Major joints:

  • Acromioclavicular joint: Connects the clavicle and scapula.

  • Glenohumeral (shoulder) joint: Ball-and-socket joint between scapula and humerus.

  • Elbow joint: Hinge joint between humerus, radius, and ulna.

  • Wrist joint: Complex joint involving radius, ulna, and carpal bones.

  • Interphalangeal joints: Hinge joints between phalanges.

Example: The shoulder joint allows for multiaxial movement, including flexion, extension, abduction, adduction, and rotation.

Articulations and Body Movements

Synovial Joint Structure

Synovial joints are the most mobile type of joint in the body and are characterized by a fluid-filled cavity. They are found in all limb joints and allow for a variety of movements.

• Ligament: Connects bone to bone, providing stability.

• Joint cavity: Contains synovial fluid for lubrication.

• Articular cartilage: Hyaline cartilage covering bone surfaces to reduce friction.

• Articular capsule: Encloses the joint, consisting of a fibrous layer and a synovial membrane.

• Synovial membrane: Secretes synovial fluid.

• Periosteum: Connective tissue covering the bone.

Additional info: Synovial fluid nourishes the articular cartilage and acts as a shock absorber.

Movements of Synovial Joints

Synovial joints allow for different types of movements depending on their structure. Movements are classified by the axes and planes in which they occur.

• Uniaxial: Movement in one plane (e.g., hinge and pivot joints).

• Biaxial: Movement in two planes (e.g., condylar joints).

• Multiaxial: Movement in multiple planes (e.g., ball-and-socket joints).

Example: The elbow joint is a hinge joint, allowing flexion and extension in one plane.

Major Types of Synovial Joints

There are several types of synovial joints, each with characteristic shapes and movement capabilities.

Additional info: The structure of each joint determines its range of motion and stability.

Actions at the Shoulder Joint

The shoulder joint (glenohumeral joint) is a multiaxial ball-and-socket joint, allowing for the greatest range of motion in the body. Movements at this joint are essential for upper limb function.

• Flexion: Raising the arm forward.

• Extension: Moving the arm backward.

• Abduction: Lifting the arm away from the body.

• Adduction: Bringing the arm toward the body.

• Medial rotation: Rotating the arm toward the midline.

• Lateral rotation: Rotating the arm away from the midline.

Example: Throwing a ball involves flexion, abduction, and rotation at the shoulder joint.

Key Terms and Definitions

• Appendicular skeleton: The portion of the skeleton that includes the limbs and girdles.

• Pectoral girdle: The set of bones (clavicle and scapula) that attach the upper limb to the trunk.

• Synovial joint: A freely movable joint characterized by a synovial cavity filled with fluid.

• Articular cartilage: Smooth, white tissue that covers the ends of bones where they come together to form joints.

• Ligament: A band of fibrous tissue connecting bones at a joint.

Formulas and Equations

While anatomy does not use many equations, understanding joint movement can involve geometric principles:

• Range of motion (ROM) can be measured in degrees:

where is the angle of movement at the joint.