Axial Skeleton: Bones and Landmarks Study Guide

Axial Skeleton Overview

Introduction

The axial skeleton forms the central framework of the human body, supporting and protecting vital organs. It consists of the skull, vertebral column, and thoracic cage. Understanding the bones and their landmarks is essential for students of anatomy and physiology.

Skull Bones and Landmarks

Frontal Bone

• Supraorbital foramen: Located above the eye socket on the frontal bone; allows passage of nerves and blood vessels.

Nasal Bone

• Landmark: On top of the nose; forms the bridge of the nose.

Sphenoid Bone

• Superior orbital fissure: Large opening between body and lesser wings; transmits cranial nerves.

• Inferior orbital fissure: Passage for nerves and vessels.

• Optic foramen (canal): Opening for the optic nerve.

• Greater wing: Prominent lateral extension.

Ethmoid Bone

• Perpendicular plate: Forms the superior part of the nasal septum.

• Superior nasal concha: Thin, scroll-like bone in the nasal cavity.

• Middle nasal concha: Second scroll-like bone in the nasal cavity.

• Cribriform plate: Contains olfactory foramina for passage of olfactory nerves.

• Crista galli: Vertical projection for attachment of brain membranes.

Lacrimal Bone

• Landmark: Forms part of the medial wall of the orbit.

Zygomatic Bone

• Temporal process: Articulates with the temporal bone to form the zygomatic arch.

Mandible

• Body: Main horizontal portion.

• Ramus: Vertical extension.

• Angle: Junction of body and ramus.

• Alveolar process: Contains tooth sockets.

• Mental foramen: Opening for nerves and vessels.

• Coronoid process: Attachment for temporalis muscle.

• Condylar process: Articulates with temporal bone.

• Mandibular notch: Depression between coronoid and condylar processes.

Maxilla

• Infraorbital foramen: Opening below the orbit for nerves and vessels.

• Palatine process: Forms the anterior part of the hard palate.

Temporal Bone

• Zygomatic process: Forms part of the zygomatic arch.

• Styloid process: Slender projection for muscle attachment.

• Mastoid process: Rounded projection for muscle attachment.

• External auditory (acoustic) meatus: Ear canal opening.

• Petrous portion: Houses structures of the inner ear.

Occipital Bone

• External occipital protuberance: Prominent bump on the posterior surface.

• Foramen magnum: Large opening for the spinal cord.

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

Other Skull Landmarks

• Coronal suture: Between frontal and parietal bones.

• Squamous suture: Between parietal and temporal bones.

• Lambdoid suture: Between parietal and occipital bones.

• Sagittal suture: Between parietal bones.

Vertebral Column

Regions and Vertebrae

• Cervical (7): Neck region.

• Thoracic (12): Upper back, articulates with ribs.

• Lumbar (5): Lower back.

• Sacral (5 fused): Forms sacrum.

• Coccygeal (3-5 fused): Forms coccyx.

Typical Vertebra Landmarks

• Body: Main weight-bearing portion.

• Pedicle: Connects body to arch.

• Lamina: Forms posterior part of arch.

• Spinous process: Posterior projection for muscle attachment.

• Transverse process: Lateral projections for muscle attachment.

• Superior/inferior articular processes: Articulate with adjacent vertebrae.

• Vertebral foramen: Canal for spinal cord.

• Intervertebral notch: Passage for spinal nerves.

Cervical Vertebrae Special Features

• Atlas (C1): Supports the skull.

• Axis (C2): Has the dens for rotation.

• C2-C6: Bifid spinous processes.

• C7: Vertebra prominens (prominent spinous process).

Thoracic Vertebrae

• T1-T12: Spinous processes and facets for rib articulation.

Lumbar Vertebrae

• L1-L5: Blunt projections for muscle attachment.

Sacrum and Coccyx

• Sacrum: Base, apex, auricular surface, sacral foramina, sacral canal, sacral hiatus, median sacral crest.

• Coccyx: Terminal portion of vertebral column.

Thoracic Cage

Sternum

• Manubrium: Upper portion; contains jugular notch.

• Body: Main portion; contains clavicular notch.

• Xiphoid process: Inferior tip.

Ribs

• 12 pairs of ribs: Protect thoracic organs.

• True ribs (1-7): Attach directly to sternum via costal cartilage.

• False ribs (8-12): Do not attach directly to sternum; ribs 11 and 12 are floating ribs.

Sinuses

Paranasal Sinuses

• Frontal sinus

• Sphenoid sinus

• Ethmoid sinus

• Maxillary sinus

HTML Table: Major Skull Bones and Landmarks

Bone	Landmark	Function/Location
Frontal	Supraorbital foramen	Above eye socket
Sphenoid	Superior orbital fissure	Passage for nerves
Ethmoid	Perpendicular plate	Forms nasal septum
Mandible	Mental foramen	Passage for nerves
Maxilla	Infraorbital foramen	Passage for nerves
Temporal	Mastoid process	Muscle attachment
Occipital	Foramen magnum	Spinal cord passage

Additional info:

• Some context and definitions have been expanded for clarity and completeness.

• Landmarks and bone features are essential for identification and understanding of anatomical relationships.