Appendicular Skeleton: Structure and Function in Anatomy & Physiology

Part 2: The Appendicular Skeleton

Overview of the Appendicular Skeleton

The appendicular skeleton consists of the bones of the limbs and their supporting girdles. It is essential for movement and interaction with the environment, connecting the limbs to the axial skeleton.

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

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

The Pectoral Girdle

Structure and Function

The pectoral girdle (shoulder girdle) is composed of the clavicles (anteriorly) and scapulae (posteriorly). It serves as the attachment point for the upper limbs and provides sites for muscle attachment, allowing for a wide range of motion.

• Attachment: Connects upper limbs to the axial skeleton.

• Mobility: High degree of mobility due to the scapulae not being directly attached to the axial skeleton and the shallow socket of the shoulder joint.

• Muscle attachment: Provides sites for muscles that move the upper limbs.

Example: The shallow glenoid cavity allows for extensive movement of the arm, but also makes the shoulder joint more susceptible to dislocation.

Clavicles

Anatomy and Articulations

The clavicles, commonly known as collarbones, are slender, S-shaped bones that serve as braces for the shoulders. They anchor muscles and keep the arms away from the thorax.

• Sternal end: Medial, cone-shaped end that articulates with the sternum.

• Acromial end: Lateral, flattened end that articulates with the scapula.

• Function: Act as braces to hold the scapulae and arms out laterally, providing structural support and muscle attachment.

Example: Fractures of the clavicle are common due to its subcutaneous position and role in transmitting forces from the upper limb to the axial skeleton.

Scapulae

Structure and Landmarks

The scapulae (shoulder blades) are thin, triangular flat bones located on the dorsal surface of the rib cage, between ribs 2 and 7. They play a crucial role in shoulder movement and stability.

• Borders: Superior (shortest, sharpest), medial (vertebral, parallel to spine), and lateral (axillary, near armpit).

• Angles: Superior, lateral, and inferior angles where borders meet.

• Key features:

  • Spine: Prominent ridge on the posterior surface.

  • Acromion: Lateral projection that articulates with the acromial end of the clavicle, forming the acromioclavicular joint.

  • Coracoid process: Anterior projection anchoring the biceps muscle.

  • Suprascapular notch: Passage for nerves.

  • Glenoid cavity: Shallow socket for the head of the humerus.

Example: The acromion and coracoid process serve as important attachment points for ligaments and muscles involved in shoulder movement.

Visual Aids

Figures and Diagrams

Figures such as "Figure 7.25 The Pectoral Girdle with Articulating Bones" and "Figure 7.26a The Clavicle" provide visual representation of the anatomical structures discussed, aiding in the understanding of bone relationships and articulations.

• Figure 7.25: Shows the relationship between the clavicle, scapula, and ribs, highlighting the acromioclavicular joint.

• Figure 7.26a: Illustrates the superior view of the right clavicle, identifying the sternal and acromial ends.

Additional info: Visual aids are essential for mastering anatomical relationships and are commonly used in anatomy and physiology courses to supplement textual descriptions.