The Skeletal System: Axial Division – Structure and Function

The Axial Skeleton

Introduction to the Axial Skeleton

The axial skeleton forms the central framework of the human body, providing support, protection, and attachment points for muscles. It is essential for maintaining posture, protecting vital organs, and facilitating movement and respiration.

• Framework and Protection: The axial skeleton supports and protects organs located in the dorsal (back) and ventral (front) body cavities, such as the brain, spinal cord, heart, and lungs.

• Special Sense Organs: It houses organs responsible for taste, smell, hearing, balance, and vision.

• Muscle Attachment: Provides sites for muscles that:

  • Adjust the posture of the head, neck, and trunk

  • Move the thoracic cage for respiration

  • Stabilize the appendicular skeleton (limbs and girdles)

Components of the Axial Skeleton

The axial skeleton consists of 80 bones, organized into three major regions:

• Skull (including cranial and facial bones)

• Vertebral column (spine)

• Thoracic cage (ribs and sternum)

These structures are highlighted in anatomical diagrams to distinguish them from the appendicular skeleton (limbs and girdles).

Skull and Associated Bones

Cranial and Facial Subdivisions of the Skull

The skull is a complex structure composed of cranial and facial bones. It protects the brain and forms the structure of the face.

• Cranial Bones (8): Enclose and protect the brain.

  • Frontal bone

  • Parietal bones (2)

  • Temporal bones (2)

  • Occipital bone

  • Sphenoid bone

  • Ethmoid bone

• Facial Bones (14): Form the structure of the face and provide cavities for the sense organs.

  • Maxillae (2)

  • Palatine bones (2)

  • Nasal bones (2)

  • Zygomatic bones (2)

  • Lacrimal bones (2)

  • Inferior nasal conchae (2)

  • Vomer (1)

  • Mandible (1)

• Associated Bones (7): Include the hyoid bone and auditory ossicles (malleus, incus, stapes in each ear).

Region	Number of Bones	Examples
Cranium	8	Frontal, Parietal (2), Temporal (2), Occipital, Sphenoid, Ethmoid
Face	14	Maxillae (2), Palatine (2), Nasal (2), Zygomatic (2), Lacrimal (2), Inferior nasal conchae (2), Vomer, Mandible
Associated Bones	7	Hyoid, Auditory ossicles (6)

Functions and Clinical Relevance

• Protection: The cranial bones form a rigid case for the brain, while facial bones protect entrances to the digestive and respiratory tracts.

• Support: The skull supports facial structures and provides attachment points for muscles involved in chewing, facial expression, and head movement.

• Clinical Note: Fractures or congenital defects in the skull can affect brain protection, sensory function, or facial symmetry.

Example: Skull Subdivisions

• Cranial bones such as the frontal and parietal bones form the vault of the skull, while the occipital bone forms the base.

• Facial bones like the maxilla and mandible are essential for mastication (chewing) and speech.

Additional info: The axial skeleton is fundamental for understanding human anatomy, as it provides the basis for the body's structure and movement. Disorders of the axial skeleton, such as scoliosis or craniosynostosis, can have significant clinical implications.