The Axial Skeleton: Structure and Function

Introduction to the Axial Skeleton

The human skeletal system is a complex framework that provides support, protection, and movement. It is divided into two main parts: the axial skeleton and the appendicular skeleton. The axial skeleton forms the central axis of the body and consists of the skull, vertebral column, and thoracic cage. In contrast, the appendicular skeleton includes the bones of the limbs and girdles.

• Total bones in adult skeleton: 206

• Axial skeleton: Skull, vertebral column, thoracic cage

• Appendicular skeleton: Shoulder and hip bones, upper and lower extremities

Overview of the Axial Skeleton

The axial skeleton provides the main support for the body and protects vital organs. It is composed of the following major components:

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

• Vertebral column: Supports the body and protects the spinal cord

• Thoracic cage: Protects the heart and lungs

Region	Components	Number of Bones
Skull	Cranial bones (8), Facial bones (14), Auditory ossicles (6), Hyoid bone (1)	29
Vertebral column	Cervical (7), Thoracic (12), Lumbar (5), Sacrum (1), Coccyx (1)	26
Thoracic cage	Sternum (1), Ribs (24)	25

Skull

Divisions of the Skull

The skull is a bony structure that encases the brain and forms the face. It is divided into cranial bones and facial bones.

• Cranial bones (8): Surround and protect the brain

  • Unpaired: Ethmoid, frontal, occipital, sphenoid

  • Paired: Parietal, temporal

• Facial bones (14): Form the structure of the face

  • Unpaired: Vomer, mandible

  • Paired: Maxillae, nasal, lacrimal, zygomatic, palatine, inferior nasal conchae

The skull contains several cavities, the largest of which is the cranial cavity that houses the brain.

Functions of the Skull

• Protection of the brain

• Support for sensory organs (eyes, ears, nose, mouth)

• Attachment sites for muscles of facial expression and mastication

Key Terms

• Cranial cavity: The space within the skull that contains the brain

• Sutures: Immovable joints between skull bones

Example: Cranial and Facial Bones

• Frontal bone: Forehead region

• Parietal bones: Sides and roof of the cranium

• Temporal bones: Lower sides of the skull

• Occipital bone: Back and base of the skull

• Maxilla: Upper jaw

• Mandible: Lower jaw

Additional info:

The skull also contains small bones such as the auditory ossicles (malleus, incus, stapes) involved in hearing, and the hyoid bone, which supports the tongue and is not directly attached to other bones.