Chapter 7: The Skeleton – Structure and Function of the Human Skeletal System

The Skeletal System

Main Divisions of the Skeleton

The human skeletal system provides the structural framework for the body, supports movement, and protects vital organs. It is composed of bones, cartilage, joints, and ligaments, and accounts for approximately 20% of total body mass.

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

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

Axial Skeleton

Overview and Functions

The axial skeleton consists of 80 bones divided into three main regions: the skull, vertebral column, and thoracic cage. Its primary functions are to support the head, neck, and trunk, protect the brain, spinal cord, and thoracic organs, and provide attachment points for muscles.

• Skull: Protects the brain and forms the structure of the face.

• Vertebral Column: Supports the trunk and protects the spinal cord.

• Thoracic Cage: Protects the heart and lungs.

Skull Structure

The skull is the most complex bony structure in the body, consisting of two sets of bones: the cranium and the facial bones.

• Cranium: Encloses the brain in the cranial cavity and provides 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, and anchor facial muscles.

• Sutures: Most skull bones are flat and firmly locked together by immovable joints called sutures, which have a serrated, saw-tooth appearance.

Cranial Bones

The cranium is composed of eight bones:

• Parietal Bones (2): Left and right; form the sides and roof of the cranial cavity.

• Temporal Bones (2): Left and right; house the structures of the ears.

• Other Cranial Bones: Frontal, occipital, sphenoid, and ethmoid bones.

Major articulations of parietal bones occur with the frontal, occipital, and temporal bones.

Major Cavities and Openings

• Orbits: House the eyeballs.

• Nasal Cavity: Contains structures for olfaction and respiration.

• Oral Cavity: Houses the teeth and tongue.

• Ear Cavities: Involved in hearing and balance.

• Foramina: Numerous openings that serve as passageways for the spinal cord, major blood vessels, and the 12 cranial nerves.

Frontal Bone

The frontal bone forms the anterior portion of the cranium, creating the forehead and the superior margins of the orbits (area under the eyebrows). It also contains the frontal sinuses, located just lateral to the glabella.

• Glabella: Smooth area between the eyebrows.

• Frontal Sinuses: Air-filled cavities that lighten the skull and enhance voice resonance.

Additional info:

• The axial skeleton provides the main support for the body and is essential for protecting the central nervous system and thoracic organs.

• Sutures are important anatomical landmarks for identifying the boundaries between cranial bones.

• Foramina are clinically significant as they allow the passage of nerves and blood vessels; damage or disease affecting these openings can have neurological consequences.