Axial Skeleton

Overview

The axial skeleton forms the central axis of the human body and includes the skull, vertebral column, thoracic cage, and hyoid bone. Understanding the terminology and anatomical features of these bones is essential for identifying structures and their functions in Anatomy & Physiology.

Cranial Bones

Frontal Bone

• Supraorbital foramen (notch): An opening above the orbit (eye socket) that allows passage of nerves and blood vessels to the forehead.

Parietal Bone

• Forms the superior and lateral aspects of the skull.

Occipital Bone

• Foramen magnum: Large opening at the base of the skull for the spinal cord to connect with the brain.

• Jugular foramen: Passage for the internal jugular vein and cranial nerves.

• Hypoglossal foramen: Passage for the hypoglossal nerve (cranial nerve XII).

• Occipital condyle: Articulates with the first cervical vertebra (atlas) to allow nodding motion of the head.

Temporal Bone

• External acoustic (auditory) canal (meatus): Canal leading to the eardrum and middle ear.

• Internal acoustic (auditory) canal (meatus): Passage for nerves of hearing and balance.

• Styloid process: Slender pointed piece of bone below the ear for muscle attachment.

• Mastoid process: Bony prominence behind the ear for muscle attachment.

• Stylomastoid foramen: Opening for the facial nerve (cranial nerve VII).

Sphenoid Bone

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

• Optic canal (foramen): Passage for the optic nerve (cranial nerve II).

• Superior orbital fissure: Slit for nerves and vessels to the orbit.

• Lesser wing & Greater wing: Bony projections forming part of the cranial floor.

• Foramen rotundum & Foramen ovale: Openings for cranial nerves.

Ethmoid Bone

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

• Cribriform plate: Contains tiny foramina for olfactory nerve fibers.

Facial Bones

• Nasal bone: Forms the bridge of the nose.

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

• Lacrimal bone: Small bone forming part of the medial orbit wall.

• Zygomatic bone: Cheekbone; forms part of the zygomatic arch.

• Zygomatic arch: Bony arch on the side of the skull formed by the zygomatic and temporal bones.

• Maxilla: Upper jaw bone; contains the infraorbital foramen.

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

• Palatine bone: Forms part of the hard palate.

• Mandible: Lower jaw bone; contains several key features:

  • Body of mandible: Horizontal portion holding the lower teeth.

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

  • Angle: Junction of the body and ramus.

  • Ramus: Vertical extension of the mandible.

  • Coronoid process: Insertion point for the temporalis muscle.

  • Condyle (condylar process): Articulates with the temporal bone to form the temporomandibular joint.

Vertebrae Structures

General Vertebrae Anatomy

• Body: Weight-bearing anterior portion.

• Pedicle: Connects the body to the transverse process.

• Lamina: Connects the transverse process to the spinous process.

• Transverse process: Lateral projections for muscle and ligament attachment.

• Spinous process: Posterior projection for muscle and ligament attachment.

• Vertebral foramen: Canal for the spinal cord.

Specific Vertebrae Types

• Cervical vertebra: Smallest vertebrae; have transverse foramina for vertebral arteries.

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

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

• Dens (odontoid process): Peg-like projection from the axis.

• Thoracic vertebra: Articulate with ribs; have long spinous processes.

• Lumbar vertebra: Largest vertebrae; support lower back.

• Sacral vertebra (sacrum): Fused vertebrae forming the posterior pelvis.

• Coccygeal vertebra (coccyx): Tailbone; small, fused vertebrae.

Thoracic Cage

Sternum

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

• Jugular (sternal) notch: Central indentation at the superior border of the manubrium.

• Sternal angle: Junction of manubrium and body; landmark for rib counting.

• Body of sternum: Main, elongated portion.

• Xiphoid process: Inferior, cartilaginous tip (ossifies with age).

Ribs

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

• False ribs (8–12): Attach indirectly or not at all to the sternum.

• Floating ribs (11 & 12): Subset of false ribs; do not attach to the sternum.

Example: "Floating rib #11" or "True rib #2" (always specify the number in practical answers).

Hyoid Bone

• U-shaped bone in the neck; does not articulate with other bones. Serves as an attachment for tongue and neck muscles.

Terminology and Practical Notes

• Indented terms are features found on the bone listed above them (e.g., supraorbital foramen is on the frontal bone).

• Structures found on multiple bones must be identified with their specific bone (e.g., body of vertebra vs. body of mandible).

• Parentheses indicate acceptable substitutions (e.g., optic canal or optic foramen).

• Terms with * indicate complete substitution is acceptable (e.g., sacrum or sacral vertebrae).

• Floating ribs are a specific type of false rib; always use the most specific term possible.

• Always include the number when identifying ribs (e.g., True Rib #4).

Summary Table: Axial Skeleton Key Structures

Additional info:

• Some anatomical terms (e.g., greater/lesser horns of hyoid) are standard but not listed in the original; included for completeness.

• For practical exams, always specify the side (left/right) and number when relevant (e.g., Left True Rib #3).