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 essential for support, movement, and protection of internal organs. The skeleton is divided into two major divisions: the axial skeleton and the appendicular skeleton.

• Axial skeleton: Forms the long axis of the body and includes the skull, vertebral column, and thoracic cage.

• Appendicular skeleton: Comprises the bones of the limbs and girdles that attach them to the axial skeleton.

Axial Skeleton

Definition and Major Regions

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

• Skull

• Vertebral column

• Thoracic cage (ribs and sternum)

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

Skull

General Structure and Function

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 and provide attachment sites 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, and anchor facial muscles for expression.

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. The major sutures include:

• Coronal Suture: Between the frontal and parietal bones

• Sagittal Suture: Between the right and left parietal bones

• Squamous Suture: Between the parietal and temporal bones

• Lambdoid Suture: Between the parietal bones and occipital bone

Key Skull Regions and Bones

• Cranial Vault (Calvaria): Forms the superior, lateral, and posterior aspects of the skull, as well as the forehead.

• Cranial Base: Forms the skull's inferior aspect and contains three cranial fossae (anterior, middle, posterior) that support different regions of the brain.

• Major Cranial Bones: Frontal, parietal (2), occipital, temporal (2), sphenoid, ethmoid.

• Facial Bones: Nasal, maxillae, zygomatic, mandible, lacrimal, palatine, vomer, inferior nasal conchae.

Functions of Skull Openings

The skull contains 85 named openings (foramina, canals, fissures) that provide passageways for the spinal cord, major blood vessels, and cranial nerves.

Example: Sutures and Bone Articulations

• The coronal suture connects the frontal bone to the parietal bones.

• The lambdoid suture connects the parietal bones to the occipital bone.

Summary Table: Major Divisions of the Skeleton

Division	Main Components	Primary Functions
Axial Skeleton	Skull, vertebral column, thoracic cage	Support, protection of central nervous system and thoracic organs
Appendicular Skeleton	Limb bones, pectoral and pelvic girdles	Movement, manipulation of environment

Additional info:

• The appendicular skeleton is not detailed in these slides but is essential for limb movement and interaction with the environment.

• Skull sutures are fibrous joints that allow for growth during childhood and fuse in adulthood.