Axial Skeleton: Structure and Function (Chapter 7 Study Notes)

The Skeleton

Overview of the Human Skeleton

The human skeleton is a structural framework composed of bones, cartilages, joints, and ligaments. It accounts for approximately 20% of total body mass and is divided into two major regions: the axial skeleton and the appendicular skeleton.

• Bones: Rigid organs that form the skeleton's structure.

• Cartilages: Flexible connective tissue found in joints and other areas.

• Joints: Sites where two or more bones meet, allowing movement.

• Ligaments: Bands of connective tissue that connect bones and stabilize joints.

Major Divisions:

• Axial skeleton: Forms the central axis of the body.

• Appendicular skeleton: Includes the limbs and girdles.

Axial Skeleton

Structure and Regions

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

• Skull

• Vertebral column

• Thoracic cage

Functions of the Axial Skeleton:

• Forms the longitudinal axis of the body

• Supports the head, neck, and trunk

• Protects the brain, spinal cord, and thoracic organs

Regional Anatomy of the Skeleton

Major Bones and Landmarks

The skeleton is divided into axial and appendicular regions, each containing specific bones and structures. The axial skeleton includes the skull, vertebral column, and thoracic cage, while the appendicular skeleton consists of the limbs and girdles.

• Skull: Cranium and facial bones

• Thoracic cage: Ribs, sternum, and thoracic vertebrae

• Vertebral column: Cervical, thoracic, lumbar vertebrae, sacrum

• Appendicular skeleton: Clavicle, scapula, humerus, radius, ulna, carpals, metacarpals, phalanges, femur, patella, tibia, fibula, tarsals, metatarsals

Example: The cranium protects the brain, while the vertebral column supports the trunk and protects the spinal cord.

The Skull

Structure and Function

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

  • Anchor facial muscles used for facial expression

Example: The maxilla secures the upper teeth and forms part of the nasal cavity.

Skull Sutures

Most skull bones are flat and firmly locked together by immovable joints called sutures (except for the mandible). Sutures have a serrated, saw-tooth appearance and are named according to the bones they connect.

• Coronal Suture: Between frontal and parietal bones

• Sagittal Suture: Between right and left parietal bones

• Squamous Suture: Between parietal and temporal bones

• Lambdoid Suture: Between parietal and occipital bones

Definition: A suture is a type of fibrous joint found only in the skull.

Summary Table: Major Divisions of the Skeleton

Division	Main Components	Functions
Axial Skeleton	Skull, vertebral column, thoracic cage	Protection, support, forms axis
Appendicular Skeleton	Limb bones, pectoral and pelvic girdles	Movement, manipulation of environment

Additional info: The axial skeleton is essential for protecting vital organs and providing structural support, while the appendicular skeleton enables locomotion and interaction with the environment.