Axial Skeleton Overview

Major Divisions of the 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 is essential for protection and support.

• Axial skeleton: Consists of 80 bones divided into three major regions: the skull, vertebral column, and thoracic cage.

• Functions:

  • Forms the longitudinal axis of the body

  • Supports the head, neck, and trunk

  • Protects the brain, spinal cord, and thoracic organs

The Skull

General Structure and Function

The skull is the most complex bony structure in the body, formed by 22 bones. It protects the brain and forms the framework of the face.

• Cranial bones (cranium): Enclose the brain in the cranial cavity

• Facial bones: Form the framework of the face

• Cavities: Provide spaces for special sense organs (sight, taste, smell)

• Openings: Provide passage for air and food

• Attachment: Provide sites for head and neck muscle attachment

Skull Bone Classification

• Most skull bones are flat and firmly locked together by sutures (except for the mandible)

• Sutures have a serrated, saw-tooth appearance

Overview of Skull Geography

• Skull is divided into two sets of bones:

  • Cranial bones: Form the cranial vault and base

  • Facial bones: Form the face

• Cranial vault: Superior, lateral, and posterior portion of the skull

• Cranial base: Inferior aspect of the skull

• Fossae: Three distinct "steps" or depressions: anterior, middle, and posterior cranial fossae

Cranial Bones

Main Cranial Bones and Features

• Frontal bone: Forms the forehead and the roof of the orbits

• Parietal bones (2): Form the superior and lateral aspects of the skull

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

• Temporal bones (2): Form the lateral aspects and base of the skull

• Sphenoid bone: Bat-shaped bone that forms part of the cranial floor

• Ethmoid bone: Forms part of the nasal cavity and the orbits

Major Cranial Sutures

• 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

Key Foramina and Processes

• Foramen magnum: Large opening in the occipital bone for the spinal cord

• Occipital condyles: Articulate with the first cervical vertebra (atlas)

• Mastoid process: Attachment site for neck muscles

• Styloid process: Attachment for tongue and neck muscles

• External acoustic meatus: Canal leading to the eardrum

Facial Bones

Main Facial Bones and Features

• Mandible: Lower jawbone; largest and strongest facial bone

• Maxillae (2): Upper jawbones; form the central portion of the face

• Zygomatic bones (2): Cheekbones

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

• Lacrimal bones (2): Form part of the medial wall of the orbits

• Palatine bones (2): Form part of the hard palate

• Vomer: Forms part of the nasal septum

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

Mandible Features

• Body: Horizontal portion forming the chin

• Ramus: Vertical portion

• Mandibular condyle: Articulates with the temporal bone to form the temporomandibular joint

• Coronoid process: Attachment for temporalis muscle

• Alveolar process: Contains sockets for teeth

Other Skull Features

Orbits and Nasal Cavity

• Orbits: House the eyes and are formed by parts of several bones

• Nasal cavity: Constructed by bone and cartilage; contains nasal conchae to increase surface area

• Paranasal sinuses: Air-filled spaces in frontal, sphenoid, ethmoid, and maxillary bones; lighten the skull and enhance voice resonance

Summary Table: Major Cranial and Facial Bones

Additional info:

• Images in the original file show labeled diagrams of the skull, cranial bones, facial bones, and their anatomical features, which are essential for visualizing bone locations and relationships.

• Some content inferred from context and standard anatomy knowledge to ensure completeness and clarity.