The Skeleton: Structure and Function of the Axial Skeleton

The Skeletal System

Overview of the Skeletal System

The skeletal system, or skeleton, is a complex framework that provides structure, protection, and movement for the human body. It is composed of bones, cartilages, joints, and ligaments.

• Bones: The primary structural component; most of the skeleton is bone tissue.

• Cartilage: Present in isolated areas, providing flexibility and cushioning.

• Ligaments: Connect bones to each other and reinforce joints.

• The skeleton accounts for approximately 20% of total body mass.

The skeleton is divided into two major divisions:

• Axial skeleton

• Appendicular skeleton

Axial Skeleton

Structure and Regions of the Axial Skeleton

The axial skeleton forms the central axis of the body and consists of 80 bones. It is divided into three major regions:

• Skull

• Vertebral column

• Thoracic cage

The axial skeleton serves three primary functions:

• Forms the longitudinal axis of the body

• Supports the head, neck, and trunk

• Protects the brain, spinal cord, and thoracic organs

The Skull

General Structure of the Skull

The skull is the most complex bony structure in the body, formed by two sets of bones:

• Cranial bones (cranium):

  • Enclose the brain in the cranial cavity

  • Provide sites of attachment for head and neck muscles

• Facial bones:

  • Form the framework of the face

  • Contain cavities for special sense organs (sight, taste, smell)

  • Provide openings for air and food passage

  • Secure the teeth

  • Anchor facial muscles used for facial expression

Most skull bones are flat and firmly locked together by joints called sutures, which have a serrated, saw-tooth appearance. The only exception is the mandible (lower jaw), which is movable.

Key Terms and Definitions

• Bone: A rigid organ that constitutes part of the vertebrate skeleton.

• Cartilage: A flexible connective tissue found in various forms in the larynx and respiratory tract, among other places.

• Ligament: A short band of tough, flexible fibrous connective tissue that connects two bones or cartilages or holds together a joint.

• Suture: An immovable joint between the bones of the skull.

Example: Functions of the Axial Skeleton

• Protection: The cranium protects the brain; the vertebral column protects the spinal cord; the thoracic cage protects the heart and lungs.

• Support: The axial skeleton supports the upright posture of the body and provides attachment points for muscles.

Additional info:

• The appendicular skeleton (not detailed in these slides) includes the bones of the limbs and girdles that attach them to the axial skeleton.

• There are 206 named bones in the adult human skeleton.