Axial Skeleton: Skull, Vertebral Column, and Bone Features Study Guide

Axial Skeleton: Overview

Objectives

The axial skeleton forms the central axis of the human body and includes the skull, vertebral column, and thoracic cage. Understanding its components and features is essential for identifying bones, articulations, and anatomical landmarks.

• Identify bones of the axial skeleton: Includes skull, vertebral column, ribs, and sternum.

• Define terms used for bone features: Learn anatomical terminology for bone markings.

• Distinguish between cranial and facial bones: Recognize the difference and location of these bones.

• Identify major skull features: Locate and name the cranial fossae, sutures, and processes.

• Recognize vertebral and thoracic bones: Understand the structure and function of vertebrae, ribs, and sternum.

Features of Bones

Bone Markings and Terminology

Bones have specific features called markings that serve as sites for muscle and ligament attachment, articulation, or passage of nerves and blood vessels. These terms are essential for describing bone anatomy.

• Process: Any bony projection.

• Tuberosity: Roughened, raised area.

• Protuberance: Projection or protrusion beyond a bone’s surface.

• Spine: Sharp, slender, often pointed projection.

• Tubercle: Small rounded projection.

• Trochanter: Very large, blunt, irregularly shaped process (only on femur).

• Fossa: Shallow basin-like depression in a bone, often an articular surface.

• Condyle: Rounded articular projection.

• Head: Bony expansion carried on a narrow neck.

• Facet: Smooth, nearly flat articular surface.

• Groove: Elongated indentation.

• Notch: Indentation at the edge of a structure.

• Fissure: Narrow slit-like opening.

• Meatus: Canal-like passageway.

Skull: Cranial and Facial Bones

Cranial Bones

The cranial bones form the cranium, which encloses and protects the brain. They also provide attachment sites for muscles.

• Frontal Bone: Forms the forehead and superior boundary of the orbits.

• Parietal Bones: Form the superior-lateral portion of the skull.

• Occipital Bone: Forms the posterior base of the skull; contains the foramen magnum.

• Temporal Bones: Located on the sides of the skull; contain mastoid and styloid processes.

• Sphenoid Bone: Forms part of the base of the skull; contains the sella turcica and greater/lesser wings.

• Ethmoid Bone: Located anterior to the sphenoid; contains cribriform plate and perpendicular plate.

Facial Bones

Facial bones form the structure of the face and provide cavities for the sense organs.

• Nasal Bones: Form the bridge of the nose.

• Lacrimal Bones: Contain the lacrimal fossa for tear drainage.

• Maxillae: Form the upper jaw and contain the upper teeth.

• Zygomatic Bones: Form the cheekbones.

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

• Palatine Bones: Form part of the hard palate.

• Inferior Nasal Conchae: Form part of the lateral walls of the nasal cavity.

• Vomer: Forms part of the nasal septum.

Skull Sutures

Sutures are immovable joints between skull bones.

• Coronal Suture: Between frontal and parietal bones.

• Sagittal Suture: Between the two parietal bones.

• Lambdoid Suture: Between parietal and occipital bones.

• Squamous Suture: Between parietal and temporal bones.

Major Skull Foramina and Fossae

Foramina are openings that allow passage of nerves and blood vessels; fossae are depressions that support brain regions.

• Foramen Magnum: Passage for spinal cord in occipital bone.

• Jugular Foramen: Passage for jugular vein and cranial nerves.

• Hypoglossal Canal: Passage for hypoglossal nerve.

• Anterior, Middle, Posterior Cranial Fossae: Depressions supporting different brain regions.

Sinuses

Sinuses are air-filled cavities within certain skull bones, visible on X-ray.

• Frontal Sinus

• Maxillary Sinus

• Ethmoid Sinus

• Sphenoid Sinus

Sinuses lighten the skull and enhance voice resonance.

Vertebral Column

Structure and Regions

The vertebral column supports the body and protects the spinal cord. It is divided into regions:

• Cervical Vertebrae: 7 vertebrae in the neck region.

• Thoracic Vertebrae: 12 vertebrae in the upper back.

• Lumbar Vertebrae: 5 vertebrae in the lower back.

• Sacrum: 5 fused vertebrae.

• Coccyx: 3-5 fused vertebrae (tailbone).

Unique Features of Cervical Vertebrae

Cervical vertebrae have distinguishing features:

• Transverse Foramina: Openings for vertebral arteries.

• Bifid Spinous Process: Split tip on some cervical vertebrae.

• Atlas (C1): Supports the skull; allows nodding motion.

• Axis (C2): Has the dens (odontoid process); allows rotation.

Tables

Bone Markings: Comparison Table

Marking	Description	Example
Process	Bony projection	Mastoid process
Fossa	Shallow depression	Mandibular fossa
Foramen	Round opening	Foramen magnum
Condyle	Rounded articular surface	Occipital condyle
Head	Expanded end carried on a neck	Head of femur
Facet	Flat articular surface	Superior articular facet

Additional Info

• Fontanelles: Soft spots on fetal skulls where bones have not yet fused; allow for growth and birth.

• TMJ (Temporomandibular Joint): Formed by the mandibular condyle and mandibular fossa of the temporal bone.

• Hyoid Bone: Unique bone in the neck not directly articulated with other bones; supports tongue and muscles.

Key Equations

No specific equations are required for bone identification, but anatomical orientation and naming conventions are essential.

Summary Table: Skull Bones

Cranial Bones	Facial Bones
Frontal	Nasal
Parietal	Lacrimal
Occipital	Maxilla
Temporal	Zygomatic
Sphenoid	Mandible
Ethmoid	Palatine
	Inferior nasal concha
	Vomer

Example Applications

• Clinical Relevance: Identifying bone features is crucial for interpreting X-rays and diagnosing fractures.

• Articulations: Understanding sutures and joints helps explain movement and stability of the skull and vertebral column.