Axial Skeleton: Lab 6 Study Guide

Axial Skeleton

Overview

The axial skeleton forms the central axis of the human body and includes the skull, vertebral column, and thoracic cage. It provides support, protection for vital organs, and attachment points for muscles.

Cranial Bones of the Skull

Frontal Bone

• Supraorbital Foramen: An opening above the orbit (eye socket) for nerves and blood vessels.

Parietal Bone

• Paired bones forming the superior and lateral aspects of the skull.

Occipital Bone

• Foramen Magnum: Large opening for the spinal cord to connect with the brain.

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

Temporal Bones

• External Auditory (Acoustic) Meatus: Canal leading to the eardrum.

• Mastoid Process: Projection for muscle attachment.

• Styloid Process: Slender pointed piece for ligament and muscle attachment.

• Zygomatic Process: Forms part of the cheekbone.

Sphenoid Bone

• Sella Turcica: Saddle-shaped depression housing the pituitary gland.

• Greater Wing: Lateral projections forming part of the skull base.

Ethmoid Bone

• Cribriform Plate: Contains tiny foramina for olfactory nerves.

• Crista Galli: Attachment for the brain's dura mater.

Cranial Sutures

• Coronal: Between frontal and parietal bones.

• Sagittal: Between the two parietal bones.

• Lambdoidal: Between parietal and occipital bones.

• Squamosal: Between parietal and temporal bones.

Fontanelles (Soft Spots)

• Anterior: Largest fontanelle, closes by 18-24 months.

• Posterior: Smaller, closes by 2-3 months.

• Sphenoidal & Mastoid: Located at the sides of the skull.

Facial Bones of the Skull

Nasal Bones

• Form the bridge of the nose.

Lacrimal Bones

• Smallest facial bones, form part of the medial orbit wall.

Maxillae (Maxillary Bones)

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

Mandible

• Mental Foramen: Openings on the anterior surface for nerves and vessels.

• Mandibular Foramen: Opening on the inner surface for nerves and vessels.

• Coronoid Process: Insertion point for the temporalis muscle.

• Mandibular Notch: Depression between coronoid and condylar processes.

• Mandibular Condyle (Condylar Process): Articulates with the temporal bone.

Palatine Bones

• Form the posterior part of the hard palate.

Vomer Bone

• Forms the inferior part of the nasal septum.

Inferior Nasal Conchae

• Curved bones in the nasal cavity that increase surface area.

Hyoid Bone

• U-shaped bone in the neck that supports the tongue and is not directly attached to other bones.

Vertebral Column

Spinal Curvatures

• Primary Curvatures: Thoracic and sacral, present at birth.

• Secondary Curvatures: Cervical and lumbar, develop after birth.

Regions of the Vertebral Column

• Cervical: 7 vertebrae (C1–C7)

• Thoracic: 12 vertebrae (T1–T12)

• Lumbar: 5 vertebrae (L1–L5)

• Sacral: 5 fused vertebrae (sacrum)

• Coccygeal: 4 fused vertebrae (coccyx)

Anatomy of a Vertebra

• Vertebral Body: Weight-bearing region.

• Vertebral Arch: Encloses the vertebral foramen.

• Spinous Process: Posterior projection for muscle/ligament attachment.

• Transverse Process: Lateral projections for muscle/ligament attachment.

• Lamina & Pedicle: Parts of the vertebral arch.

Regional Differences in Vertebrae

• Cervical Vertebrae: Smallest, have transverse foramina. C1 (Atlas) and C2 (Axis) are specialized for head movement.

• Thoracic Vertebrae: Larger, have costal facets for rib articulation, angled spinous processes.

• Lumbar Vertebrae: Largest, thick bodies, short blunt spinous processes.

• Sacrum: 5 fused vertebrae forming the posterior pelvic wall.

• Coccyx: 4 fused vertebrae forming the tailbone.

Thoracic (Rib) Cage

Sternum

• Manubrium: Superior portion, articulates with clavicles and first ribs.

• Jugular Notch: Central indentation at the superior border.

• Body: Main, elongated part of the sternum.

• Sternal Angle (Angle of Louis): Junction of manubrium and body, landmark for rib counting.

• Xiphoid Process: Inferior, small cartilaginous process.

Ribs

• Vertebrosternal (True Ribs): Pairs 1–7, attach directly to the sternum via costal cartilage.

• Vertebrochondral (False Ribs): Pairs 8–10, attach indirectly to the sternum.

• Vertebral (Floating Ribs): Pairs 11 & 12, do not attach to the sternum.

Summary Table: Vertebral Column Regions

Region	Number of Vertebrae	Key Features
Cervical	7	Transverse foramina, small bodies, bifid spinous processes (except C7)
Thoracic	12	Costal facets for ribs, long downward spinous processes
Lumbar	5	Large bodies, short blunt spinous processes
Sacrum	5 (fused)	Triangular, forms posterior pelvic wall
Coccyx	4 (fused)	Small, tailbone

Example: Atlas and Axis

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

• Axis (C2): Has the dens (odontoid process) for rotation of the head.

Additional info: The axial skeleton is essential for protecting the brain, spinal cord, and thoracic organs, and serves as a framework for muscle attachment and movement.