Appendicular Skeleton: Structure and Function of the Upper Limb

The Appendicular Skeleton

Overview of the Appendicular Skeleton

The appendicular skeleton consists of the bones that support the limbs and allow for movement. It is divided into the pectoral (shoulder) girdle, pelvic girdle, and the bones of the upper and lower limbs. The appendicular skeleton is essential for locomotion and manipulation of the environment.

• Pectoral girdle: Attaches the upper limbs to the trunk.

• Pelvic girdle: Attaches the lower limbs to the trunk.

• Upper and lower limbs differ in function but share a similar structural plan.

The Pectoral Girdle

Structure and Function

The pectoral girdle consists of two bones: the clavicle and the scapula. It provides attachment for muscles that move the upper limb and allows for a wide range of motion.

• Only the clavicle articulates with the axial skeleton.

• The socket of the shoulder joint (glenoid cavity) is shallow, which increases flexibility but decreases stability.

Articulated Pectoral Girdle

The pectoral girdle connects the upper limb to the trunk via the clavicle and scapula, forming the shoulder region.

• Clavicle: Articulates with the sternum at the sternoclavicular joint.

• Scapula: Articulates with the clavicle and humerus.

Clavicles

Structure and Function

The clavicles are slender, S-shaped bones that extend horizontally across the superior thorax. They serve as struts to hold the scapulae and arms laterally and transmit compression forces from the upper limbs to the axial skeleton.

• Sternal end: Articulates with the manubrium of the sternum.

• Acromial end: Articulates with the scapula.

• Provide attachment for muscles.

Key Landmarks of the Clavicle

• Conoid tubercle: Attachment site for ligaments.

• Trapezoid line: Attachment site for ligaments.

Scapulae

Structure and Borders

The scapulae are flat, triangular bones located on the dorsal surface of the rib cage, between ribs 2–7. Each scapula has three borders and three angles.

• Borders: Superior, medial (vertebral), lateral (axillary).

• Angles: Lateral, superior, inferior.

Structures of the Scapula

• Acromion: Articulates with the clavicle.

• Coracoid process: Attachment for muscles.

• Glenoid cavity: Articulates with the humerus.

• Supraspinous fossa and infraspinous fossa: Muscle attachment sites.

The Upper Limb

Overview

The upper limb consists of 30 bones and is grouped into three regions: the arm, forearm, and hand. These bones provide the framework for movement and manipulation.

• Arm: Humerus

• Forearm: Radius and ulna

• Hand: Carpals, metacarpals, phalanges

Arm

Humerus

The humerus is the only bone of the arm and is the longest and strongest bone of the upper limb. It articulates with the scapula at the shoulder and with the radius and ulna at the elbow.

• Provides sites for muscle attachment.

• Articulates with other bones to form joints.

Key Structures of the Humerus

• Head: Articulates with the glenoid cavity of the scapula.

• Greater and lesser tubercles: Muscle attachment sites.

• Capitulum: Articulates with the radius.

• Trochlea: Articulates with the ulna.

• Olecranon fossa: Receives the olecranon of the ulna during elbow extension.

Forearm

Radius and Ulna

The forearm is formed by two parallel bones: the radius and ulna. These bones articulate with each other at the proximal and distal radioulnar joints and are connected by the interosseous membrane.

• Proximal ends articulate with the humerus.

• Distal ends articulate with the carpals.

• In anatomical position, the radius is lateral and the ulna is medial.

Ulna

The ulna is the main bone responsible for forming the elbow joint with the humerus. It acts as a hinge joint, allowing the forearm to bend and straighten.

• Distal end is separated from carpals by fibrocartilage.

• Plays little to no role in hand movement.

Key Structures of the Ulna

• Olecranon process: Forms the point of the elbow.

• Coronoid process: Articulates with the humerus.

• Radial notch: Articulates with the head of the radius.

Radius

The radius is located on the lateral side of the forearm and is crucial for wrist movement. Its head articulates with the capitulum of the humerus and the radial notch of the ulna.

• Distal end articulates with carpal bones.

• When the radius moves, the hand moves with it.

Summary Table: Bones of the Upper Limb

Region	Main Bones	Key Functions
Pectoral Girdle	Clavicle, Scapula	Attaches upper limb to trunk, muscle attachment
Arm	Humerus	Movement at shoulder and elbow, muscle attachment
Forearm	Radius, Ulna	Movement at elbow and wrist, muscle attachment
Hand	Carpals, Metacarpals, Phalanges	Manipulation, dexterity

Key Terms and Definitions

• Pectoral girdle: The set of bones that connects the upper limb to the axial skeleton.

• Clavicle: A long bone that serves as a strut between the shoulder blade and the sternum.

• Scapula: Also known as the shoulder blade, a flat bone that provides attachment for several muscles.

• Humerus: The bone of the upper arm.

• Ulna: The medial bone of the forearm, forming the elbow joint with the humerus.

• Radius: The lateral bone of the forearm, important for wrist movement.

Example: Articulation of the Elbow Joint

The elbow joint is formed by the articulation of the humerus with the ulna and radius. The trochlea of the humerus fits into the trochlear notch of the ulna, allowing for hinge-like movement. The capitulum of the humerus articulates with the head of the radius, permitting rotation of the forearm.

Additional info:

• The interosseous membrane between the radius and ulna stabilizes the forearm and provides additional surface area for muscle attachment.

• Muscle attachments on the scapula include the rotator cuff muscles, which stabilize the shoulder joint.