The Skeleton: Structure and Anatomy of the Skull

The Skeleton

Overview of the Skeletal System

The skeletal system, or skeleton, is a complex framework of bones that provides structure, protection, and movement for the human body. It is divided into two main divisions: the axial skeleton and the appendicular skeleton.

• Axial skeleton: Forms the central axis of the body and includes the skull, vertebral column, and thoracic cage.

• Appendicular skeleton: Consists of the limbs and girdles that attach them to the axial skeleton.

• There are 206 named bones in the adult human skeleton.

• Bones are classified by shape: long, short, flat, and irregular.

Objectives

• Learn the bones of the human body.

• Be familiar with key bone markings to help identify specific bones.

The Human Skeleton

Major Divisions

• Axial skeleton: 80 bones (skull, vertebral column, thoracic cage)

• Appendicular skeleton: 126 bones (limbs and girdles)

The Axial Skeleton

Components and Functions

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

• Skull: Protects the brain and forms the structure of the face.

• Vertebral column: Supports the body and protects the spinal cord.

• Thoracic cage: Protects the heart, lungs, and major thoracic organs.

Functions:

• Support and protect organs in the dorsal and ventral body cavities.

• Provide surface area for the attachment of muscles.

The Skull

General Structure and Function

The skull is the most complex bony structure in the body, formed by two sets of bones:

• Cranial bones (cranium): Enclose and protect the brain, provide attachment for head and neck muscles.

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

Most skull bones are flat and firmly locked together by immovable joints called sutures, except for the mandible (lower jaw).

Overview of Skull Geography

• Skull bones form two major sets: the cranial vault (calvaria) and the cranial base.

• The cranial vault forms the superior, lateral, and posterior aspects of the skull.

• The cranial base forms the inferior aspect and contains three distinct fossae: anterior, middle, and posterior cranial fossae.

• The cranial cavity houses the brain.

• Other cavities include the middle and inner ear, nasal cavity, orbits, and paranasal sinuses.

Major Cavities of the Skull

• Cranial cavity: Encloses the brain.

• Orbits: House the eyes.

• Nasal cavity: Contains structures for olfaction and respiration.

• Paranasal sinuses: Air-filled spaces that lighten the skull and enhance voice resonance.

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

Cranium

Major Cranial Bones

The cranium is composed of eight cranial bones:

• Frontal bone

• Parietal bones (left and right)

• Occipital bone

• Temporal bones (left and right)

• Sphenoid bone

• Ethmoid bone

Views of the Skull

• Anterior view: Shows the frontal, nasal, zygomatic, maxilla, and mandible bones.

• Base of the cranial cavity: Shows the arrangement of the cranial fossae and foramina.

• Lateral and posterior views: Highlight the temporal, parietal, and occipital bones.

Major Sutures of the Skull

• Coronal suture: Between frontal and parietal bones.

• Sagittal suture: Between right and left parietal bones.

• Lambdoid suture: Between parietal bones and occipital bone.

• Squamous suture: Between parietal and temporal bones.

Occipital Bone

• Forms the posterior part of the skull and cranial base.

• Contains the foramen magnum, a large opening for the spinal cord.

• Articulates with the first vertebra (atlas) via the occipital condyles.

Temporal Bones

• Form the inferolateral aspects of the skull and parts of the cranial base.

• Contain important structures such as the external acoustic meatus (ear canal) and mastoid process.

• Provide attachment for muscles and house structures of the middle and inner ear.

Sphenoid Bone

• Bat-shaped bone that spans the width of the middle cranial fossa.

• Contains the sella turcica, which houses the pituitary gland.

• Articulates with all other cranial bones.

• Contains important foramina for nerves and blood vessels.

Ethmoid Bone

• Deepest skull bone, located between the nasal cavity and orbits.

• Forms part of the nasal septum and the medial wall of the orbits.

• Contains the cribriform plate for olfactory nerve passage.

Sutural Bones

• Tiny, irregularly shaped bones that appear within sutures.

• Significance is unknown; not everyone has them.

Facial Bones

Overview

The facial skeleton consists of 14 bones, which form the framework of the face, contain cavities for special sense organs, and provide openings for air and food passage.

• Mandible (1)

• Maxillae (2)

• Zygomatic bones (2)

• Nasal bones (2)

• Lacrimal bones (2)

• Palatine bones (2)

• Vomer (1)

• Inferior nasal conchae (2)

Middle Ear Bones

Auditory Ossicles

• Three small bones: malleus, incus, and stapes.

• Transmit sound vibrations from the eardrum to the inner ear.

• Smallest bones in the human body.

Clinical Note: Homeostatic Imbalance

• Mastoiditis: Inflammation of the mastoid process, which can result from middle ear infections spreading to the mastoid air cells.

• Potentially serious due to proximity to the brain.

Summary Table: Major Cranial Bones and Key Features

Bone	Location	Key Features
Frontal	Forehead, superior part of orbits	Supraorbital foramen, frontal sinuses
Parietal (2)	Superior and lateral aspects of skull	Joined by sagittal suture
Occipital	Posterior skull, cranial base	Foramen magnum, occipital condyles
Temporal (2)	Inferolateral skull, cranial base	External acoustic meatus, mastoid process
Sphenoid	Base of skull, spans width	Sella turcica, optic canal
Ethmoid	Between nasal cavity and orbits	Cribriform plate, perpendicular plate

Additional info:

• The notes provide a foundational overview of the skull and cranial bones, suitable for introductory Anatomy & Physiology courses.

• For further study, students should learn the detailed anatomy of each bone, including foramina, processes, and articulations.