Axial Skeleton: The Skull – Structure and Components

Axial Skeleton: The Skull

Overview of the Skull

The skull is a complex bony structure that forms the head in vertebrates. It serves to protect the brain, support the structures of the face, and provide attachment points for muscles. The human skull is divided into two main groups of bones: the cranial bones and the facial bones.

• Cranial bones: Enclose and protect the brain.

• Facial bones: Form the structure of the face and house the openings for the digestive and respiratory tracts.

Cranial Bones

Major Cranial Bones and Their Functions

The cranium consists of eight bones that are tightly joined together by immovable joints called sutures. These bones collectively protect the brain and form the cranial cavity.

• Frontal bone: Forms the forehead and the upper part of the eye sockets (orbits).

• Parietal bones (2): Form the sides and roof of the cranial cavity.

• Occipital bone: Forms the back and base of the skull; contains the foramen magnum for passage of the spinal cord.

• Temporal bones (2): Form the lower sides of the skull and house the structures of the ears.

• Sphenoid bone: Located at the base of the skull, it helps connect the cranial and facial bones; contains the sella turcica, which houses the pituitary gland.

• Ethmoid bone: Located between the eyes, it forms part of the nasal cavity and the orbits.

Example: The foramen magnum in the occipital bone allows the spinal cord to connect with the brain.

Facial Bones

Major Facial Bones and Their Functions

The facial skeleton consists of fourteen bones that shape the face, form the cavities for the sense organs, and provide openings for air and food passage.

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

• Lacrimal bones (2): Small bones forming part of the medial wall of each orbit; contain the lacrimal fossa for tear drainage.

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

• Zygomatic bones (2): Form the cheekbones and part of the lateral wall of each orbit.

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

• Vomer bone: Forms the inferior part of the nasal septum.

• Maxillae (2): Form the upper jaw and part of the hard palate, orbits, and nasal cavity.

• Mandible: Forms the lower jaw; the only movable bone of the skull.

Example: The mandible articulates with the temporal bone at the temporomandibular joint, allowing for movement during chewing.

Sutures of the Skull

Major Sutures and Their Locations

Sutures are immovable joints that connect the bones of the skull. They are important anatomical landmarks and contribute to the strength and stability of the skull.

• Coronal suture: Between the frontal and parietal bones.

• Sagittal suture: Between the two parietal bones.

• Lambdoid suture: Between the parietal bones and the occipital bone.

• Squamous suture: Between the parietal and temporal bones.

Example: The coronal suture is visible as a transverse line across the top of the skull.

Special Features of Cranial Bones

Key Structures and Landmarks

• External auditory meatus: Opening in the temporal bone for the ear canal.

• Sella turcica: Depression in the sphenoid bone that houses the pituitary gland.

• Mental foramen: Opening in the mandible for nerves and blood vessels.

• Alveolar margin: Ridge containing the sockets for teeth in the maxilla and mandible.

Example: The mental foramen is palpable on the anterior surface of the mandible.

Bones of the Orbit

Composition of the Eye Socket

The orbit is a bony cavity that houses the eye and its associated structures. It is formed by contributions from several cranial and facial bones.

• Frontal bone

• Ethmoid bone

• Sphenoid bone

• Lacrimal bone

• Palatine bone

• Maxilla

• Zygomatic bone

• Nasal bone

Example: The lacrimal bone contains the lacrimal fossa, which helps drain tears from the eye into the nasal cavity.

Hyoid Bone

Structure and Function

The hyoid bone is a unique U-shaped bone located in the neck, not directly attached to other bones. It serves as an anchoring structure for the tongue and muscles associated with swallowing.

• Body: Central part of the hyoid bone.

• Greater horn: Projects backward from the body.

• Lesser horn: Projects upward from the body.

Example: The hyoid bone is fractured in cases of strangulation.

Summary Table: Cranial and Facial Bones

Bone Group	Bones	Number	Main Function
Cranial	Frontal, Parietal, Occipital, Temporal, Sphenoid, Ethmoid	8	Protects brain, forms cranial cavity
Facial	Nasal, Lacrimal, Palatine, Zygomatic, Inferior nasal conchae, Vomer, Maxilla, Mandible	14	Forms face, supports openings for air/food, anchors teeth

Additional info: The notes and images provided are consistent with standard college-level Anatomy & Physiology coverage of the axial skeleton, specifically the skull. All major bones, sutures, and anatomical landmarks have been expanded with academic context for clarity and completeness.