Study Notes: The Skeletal System – Anatomy of the Skull and Axial Skeleton

The Skeletal System

Overview of the Skeletal System

The skeletal system forms the structural framework of the human body, providing support, protection, and facilitating movement. It consists of bones, cartilage, ligaments, and joints, and is divided into two main parts: the axial skeleton and the appendicular skeleton.

• Axial Skeleton: Includes the skull, vertebral column, and thoracic cage.

• Appendicular Skeleton: Comprises the limbs and girdles (pectoral and pelvic).

Example: The skull protects the brain, while the rib cage shields the heart and lungs.

Anatomy of the Skull

Anterior and Posterior Aspects of the Skull

The skull is a complex structure composed of several bones that protect the brain and form the face. It is divided into the cranium (which encases the brain) and the facial bones.

• Anterior View: Shows the facial bones, orbits (eye sockets), nasal cavity, and maxilla (upper jaw).

• Posterior View: Highlights the occipital bone and parietal bones, which form the back and sides of the cranium.

Key Bones:

• Frontal Bone: Forms the forehead and upper part of the eye sockets.

• Parietal Bones: Paired bones forming the sides and roof of the cranium.

• Occipital Bone: Forms the back and base of the skull.

• Temporal Bones: Located at the sides and base of the skull.

• Sphenoid Bone: Butterfly-shaped bone at the base of the skull, visible from multiple views.

• Ethmoid Bone: Located between the eyes, contributes to the medial wall of the orbits and nasal cavity.

• Maxilla: Upper jaw bone, forms part of the orbit and supports the upper teeth.

• Mandible: Lower jaw bone, the only movable bone of the skull.

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

Functions of Skull Bones

• Protection: Encases and protects the brain and sensory organs.

• Support: Provides attachment points for muscles of facial expression and mastication.

• Formation of Cavities: Forms the orbits, nasal cavity, and oral cavity.

Classification of Skull Bones

• Cranial Bones: 8 bones forming the cranium (frontal, parietal [2], temporal [2], occipital, sphenoid, ethmoid).

• Facial Bones: 14 bones forming the face (maxilla [2], palatine [2], zygomatic [2], nasal [2], lacrimal [2], inferior nasal concha [2], vomer, mandible).

Table: Major Bones of the Skull and Their Locations

Bone	Location	Function
Frontal	Forehead, upper orbit	Protection, muscle attachment
Parietal	Sides and roof of cranium	Protection
Occipital	Back and base of skull	Protection, foramen magnum passage
Temporal	Lower sides of skull	Protection, hearing structures
Sphenoid	Base of skull, behind eyes	Structural support, forms part of orbit
Ethmoid	Between eyes, nasal cavity	Supports nasal cavity, forms part of orbit
Maxilla	Upper jaw, part of orbit	Supports teeth, forms facial structure
Mandible	Lower jaw	Supports teeth, movement for chewing

Additional info:

• The skull also contains foramina (holes) for the passage of nerves and blood vessels, such as the infraorbital foramen in the maxilla.

• Sinuses within certain skull bones (frontal, sphenoid, ethmoid, maxilla) lighten the skull and enhance voice resonance.