Study Notes: The Skeleton – Axial Skeleton and Skull (Anatomy & Physiology)

The Skeleton: Overview

Introduction to the Human Skeleton

The human skeleton is a structural framework composed of bones, cartilage, joints, and ligaments. It provides support, protection, and facilitates movement. The skeleton accounts for approximately 20% of total body mass and is divided into two major parts:

• Axial skeleton

• Appendicular skeleton

The Axial Skeleton

Structure and Components

The axial skeleton forms the central axis of the body and consists of 80 bones. It is organized into three major regions:

• Skull

• Vertebral column

• Thoracic cage

These regions protect vital organs and provide attachment points for muscles.

The Skull

General Features

The skull is a complex structure formed by two sets of bones:

• Cranial bones (cranium): Enclose and protect the brain within the cranial cavity.

• Facial bones: Form the framework of the face, house special sense organs, and provide openings for air and food passage.

The skull also serves as an attachment site for muscles involved in facial expression and mastication.

Cranial and Facial Divisions

• Cranial bones: Frontal, parietal, occipital, temporal, sphenoid, and ethmoid bones.

• Facial bones: Maxilla, mandible, zygomatic, nasal, lacrimal, palatine, inferior nasal concha, and vomer.

Major sutures (immovable joints) connect the bones of the skull, including the coronal, sagittal, lambdoid, and squamous sutures.

Skull Geography

Key Anatomical Features

• Cranial cavity: Houses the brain.

• Middle and internal ear cavities: Involved in hearing and balance.

• Nasal cavity: Passage for air and olfaction.

• Orbits: Contain the eyes.

• Openings: Foramina, canals, and fissures allow passage of nerves and blood vessels.

Cranial Fossae

Divisions and Functions

• Anterior cranial fossa: Supports the frontal lobes of the brain.

• Middle cranial fossa: Accommodates the temporal lobes.

• Posterior cranial fossa: Contains the cerebellum.

These fossae are depressions in the cranial base that house different regions of the brain.

Major Cranial Bones

Frontal Bone

• Forms the anterior portion of the cranium and the forehead.

• Contains the frontal sinus.

• Contributes to the superior wall of the orbits.

Parietal Bones

• Form the superior and lateral aspects of the cranial vault.

• Articulated by four major sutures:

Suture	Location
Coronal	Between parietal and frontal bones
Sagittal	Between right and left parietal bones
Lambdoid	Between parietal and occipital bones
Squamous	Between parietal and temporal bones

Occipital Bone

• Forms the posterior wall and base of the skull.

• Contains the foramen magnum for passage of the spinal cord.

• Articulates with the first vertebra (atlas).

• Provides attachment for ligamentum nuchae and neck/back muscles.

Temporal Bones

• Located on the lateral aspects of the skull.

• Contribute to the cranial floor.

• Four major regions:

  • Squamous

  • Tympanic

  • Mastoid

  • Petrous

Sphenoid Bone

• Complex, bat-shaped bone located at the base of the skull.

• Keystone bone: articulates with all other cranial bones.

• Contains three pairs of processes:

  • Greater wings

  • Lesser wings

  • Pterygoid processes

Ethmoid Bone

• Forms part of the anterior cranial base, nasal cavity, and orbits.

• Contains the cribriform plate and perpendicular plate.

Summary Table: Major Cranial Bones and Features

Bone	Main Features	Function
Frontal	Forehead, superior orbit, frontal sinus	Protects brain, forms face
Parietal	Superior/lateral skull, sutures	Protects brain
Occipital	Posterior skull, foramen magnum	Protects brain, spinal cord passage
Temporal	Lateral skull, ear structures	Protects brain, hearing/balance
Sphenoid	Central base, wings/processes	Articulates with all cranial bones
Ethmoid	Anterior base, nasal cavity	Supports nasal cavity, olfaction

Key Terms and Definitions

• Suture: An immovable joint between skull bones.

• Foramen: An opening in bone for nerves and blood vessels.

• Process: A projection or outgrowth of bone for muscle attachment.

• Fossa: A depression or hollow in bone.

Additional info:

• The appendicular skeleton (not covered in detail here) includes the bones of the limbs and girdles.

• Facial bones also contribute to the formation of the nasal and oral cavities.