Axial Skeleton: Structure and Components

Axial Skeleton

Overview of the Human Skeleton

The human skeleton is divided into two major parts: the axial skeleton and the appendicular skeleton. The axial skeleton forms the central axis of the body and provides support and protection for the brain, spinal cord, and thoracic organs.

• Axial Skeleton: Includes the skull, vertebral column, and thoracic cage (ribs and sternum).

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

Main regions of the axial skeleton:

• Skull (including the hyoid bone)

• Vertebral column

• Thoracic cage (ribs and sternum)

Functions of the Axial Skeleton

• Supports and protects the organs of the head, neck, and trunk.

• Provides attachment points for muscles that move the head, neck, and trunk.

• Serves as the main framework for the body’s posture and stability.

The Skull

General Structure

The skull consists of 22 bones, which are grouped into cranial and facial bones. These bones are joined together by immovable joints called sutures (except for the mandible).

• Cranial bones (8): Enclose the brain in the cranial cavity and provide attachment sites for head and neck muscles.

• Facial bones (14): Form the framework of the face, create cavities for special sense organs (sight, taste, smell), provide openings for air and food passage, and serve as attachment sites for teeth and muscles of facial expression.

Cranial Bones

• Frontal bone: Forms the forehead and the superior part of the orbits.

• Parietal bones (2): Form the superior and lateral aspects of the cranial vault.

• Occipital bone: Forms the posterior part of the skull and base; contains the foramen magnum.

• Temporal bones (2): Form the inferolateral aspects of the skull and part of the cranial base.

• Sphenoid bone: Bat-shaped bone that is the keystone of the cranium, articulating with all other cranial bones.

• Ethmoid bone: Deepest skull bone; forms part of the nasal septum and the medial wall of the orbits.

Facial Bones

• Mandible: Lower jaw; the largest and strongest facial bone; only freely movable joint in the skull (temporomandibular joint).

• Maxillary bones (2): Form the upper jaw and central portion of the facial skeleton; articulate with all other facial bones except the mandible.

• Zygomatic bones (2): Cheekbones; form the inferolateral margins of the orbits.

• Nasal bones (2): Form the bridge of the nose.

• Lacrimal bones (2): Form part of the medial walls of the orbits; contain the lacrimal fossa for the lacrimal sac.

• Palatine bones (2): Form the posterior part of the hard palate and part of the nasal cavity and orbits.

• Vomer: Forms part of the nasal septum.

• Inferior nasal conchae (2): Form part of the lateral walls of the nasal cavity.

Key Functions of Skull Bones

• Protection of the brain and sensory organs.

• Support for facial structures and teeth.

• Passageways for nerves and blood vessels.

Example: Sutures of the Skull

• Coronal suture: Between frontal and parietal bones.

• Sagittal suture: Between the two parietal bones.

• Lambdoid suture: Between parietal and occipital bones.

• Squamous suture: Between parietal and temporal bones.

Summary Table: Major Bones of the Axial Skeleton

Region	Major Bones	Key Functions
Skull	Cranial (8), Facial (14)	Protects brain, supports facial structures
Vertebral Column	Cervical (7), Thoracic (12), Lumbar (5), Sacrum (1), Coccyx (1)	Supports trunk, protects spinal cord
Thoracic Cage	Sternum, Ribs (24)	Protects thoracic organs, supports upper limbs

Additional info:

• The hyoid bone, though not part of the skull, is associated with the axial skeleton and serves as an attachment for tongue and neck muscles.

• The axial skeleton provides the main support for the body and is essential for movement and protection of vital organs.