The Skeletal System

Overview

The skeletal system is a fundamental component of human anatomy, providing structure, protection, and support for movement. It is divided into two main regions: the axial skeleton and the appendicular skeleton. Understanding the organization and function of these divisions is essential for students of anatomy and physiology.

• Axial Skeleton: Composed of the skull, vertebral column, and thoracic cage. It supports and protects the brain, spinal cord, and organs in the thorax.

• Appendicular Skeleton: Includes the limbs and girdles (pectoral and pelvic) that attach them to the axial skeleton. It is primarily responsible for movement and manipulation of objects.

Divisions of the Skeleton

Axial vs. Appendicular Skeleton

The skeleton is organized into two major divisions, each with distinct functions and components.

Appendicular Skeleton

General Features

The appendicular skeleton consists of the bones of the limbs and the girdles that attach them to the axial skeleton. It is essential for locomotion and manipulation of objects.

• Pectoral Girdle: Connects the upper limbs to the trunk; includes the clavicle and scapula.

• Pelvic Girdle: Connects the lower limbs to the trunk; includes the hip bones (ilium, ischium, pubis).

• Upper Limbs: Humerus, radius, ulna, carpals, metacarpals, phalanges.

• Lower Limbs: Femur, tibia, fibula, tarsals, metatarsals, phalanges.

Note: The appendicular skeleton contains more bones than the axial skeleton and is specialized for a wide range of movements.

Pectoral Girdle

Structure and Function

The pectoral girdle consists of the clavicle and scapula, which together provide attachment points for muscles and facilitate movement of the upper limb.

• Clavicle: S-shaped bone that acts as a strut between the sternum and scapula.

• Scapula: Flat, triangular bone located on the posterior thorax; provides attachment for muscles and articulates with the humerus at the shoulder joint.

• Shoulder Joint: Highly mobile joint allowing for a wide range of arm movements.

Example: The acromioclavicular joint is where the clavicle meets the acromion of the scapula, providing stability and flexibility to the shoulder.

Scapula

Landmarks and Regions

The scapula is a key bone of the pectoral girdle, with several important anatomical features.

• Spine of Scapula: A prominent ridge dividing the posterior surface into the supraspinous and infraspinous fossae.

• Medial Border: The edge closest to the vertebral column.

• Lateral Border: The edge closest to the arm.

• Acromion Process: Extension of the spine; articulates with the clavicle.

• Glenoid Cavity: Shallow socket that articulates with the head of the humerus.

• Subscapular Fossa: Broad depression on the anterior surface for muscle attachment.

Example: The supraspinous fossa is located above the spine of the scapula and serves as the origin for the supraspinatus muscle.

Key Terms and Definitions

• Fossa: A shallow depression or hollow in a bone, often serving as a site for muscle attachment.

• Process: A projection or outgrowth of bone for muscle or ligament attachment.

• Articulation: The point where two bones meet, forming a joint.

Summary Table: Major Bones of the Appendicular Skeleton

Additional info: The notes reference anatomical positions and views (e.g., posterior, superior) to help students visualize bone landmarks and relationships. Understanding these orientations is crucial for identifying structures in lab and clinical settings.