Axial Skeleton and Skull Anatomy

Overview of the Axial Skeleton

  • The axial skeleton is the central part of the human skeleton, consisting of a total of 80 bones.
  • It includes:
    • The skull
    • The vertebral column
    • The thoracic cage (comprising the ribs and the sternum)
  • It excludes bones related to the limbs: hips, shoulders, arms, and legs.

Details of the Skull

  • The skull is comprised of 22 bones:
    • Facial bones: Form the anterior part of the skull.
    • Cranial bones: Form the posterior part of the skull.
  • Important to understand the sutural junctions where bones meet.

Functions of the Skull

  • Anchors the teeth: Teeth sit in sockets located in the mandible and maxilla.
  • Houses special sense organs: Including eyes (sight), nose (smell), ears (hearing), and tongue (taste).
  • Protects the brain: The skull encases the brain, providing physical protection.
  • Forms the face: The arrangement of the facial bones creates individual facial features.
  • Attachment of muscles: Numerous flat surfaces on the skull provide points for muscle attachment aiding expressions and movements.
  • Forms openings for respiratory and digestive systems: These include the mouth leading to the throat and the nasal passages.

Composition of the Cranium

  • The cranium specifically includes 8 bones:
    • 2 temporal bones
    • 2 parietal bones
    • 1 frontal bone
    • 1 occipital bone
    • 1 sphenoid bone
    • 1 ethmoid bone

Structure of the Skull

  • Top of the skull: Known as the calvaria or skull cap, which covers the brain.
  • Base of the skull: Referred to as the cranial floor, supporting the brain in three fossa: posterior, middle, and anterior.
  • Definitions:
    • Fossa: A flat depression in the skull where structures may sit.

Sinuses

  • Sinuses: Air-filled cavities lined with mucous membranes located within certain skull bones.
    • Functions include lightening the skull, warming, and moisturizing the air during respiration, and acting as resonance chambers for voice.
  • Types of sinuses:
    • Frontal sinus
    • Maxillary sinus
    • Sphenoidal sinus
    • Ethmoidal sinus

Details of Specific Cranial Bones

Frontal Bone

  • Forms the brow ridge and the supraorbital foramen (where vessels/nerves pass through).
  • Defines the forehead (frontal squama) and the superior aspect of the orbit (eye socket).
  • Creates the anterior cranial fossa where the frontal lobe of the brain sits.

Parietal Bone

  • Consists of two bones forming the superior and lateral aspects of the skull.
  • Key sutures include:
    • Coronal suture: Separates the frontal and parietal bones.
    • Sagittal suture: Midline suture dividing the two parietal bones.
    • Lambdoidal suture: Separates the parietal bones from the occipital bone.
    • Squamous suture: Separate temporal and parietal bones.

Occipital Bone

  • Located at the posterior and inferior aspects of the skull.
  • Forms the posterior cranial fossa and contains the foramen magnum (large hole for spinal cord).
  • Houses the occipital condyles, which articulate with the first vertebra, and the hypoglossal canals for cranial nerve XII.

Temporal Bone

  • Known as the temple area with several subdivisions:
    • Squamous region: Contains zygomatic process (part of cheekbone) and mandibular fossa (where mandible sits).
    • Tympanic region: Houses the external auditory meatus (ear canal).
    • Mastoid region: Contains the mastoid process and the mastoid sinus.
    • Petrous region: Houses middle and internal ear structures and contains carotid canal.

Sphenoid Bone

  • Described as having a central body and three processes:
    • Greater Wings: Larger sections extending laterally.
    • Lesser Wings: Smaller extensions above the greater wings.
    • Pterygoid Processes: Shaped like feet of a butterfly.
  • Houses sella turcica, the depression for the pituitary gland, and several significant openings for cranial nerves and blood vessels:
    • Optic foramen
    • Superior orbital fissure
    • Foramen rotundum
    • Foramen ovale
    • Foramen spinosum

Ethmoid Bone

  • Position is posterior to the nose, responsible for nasal structure and sinuses.
  • Contains:
    • Perpendicular plate: Forms superior part of nasal septum.
    • Olfactory foramina: Holes for olfactory nerve passage, facilitating the sense of smell.
    • Crista galli: Pointed structure for brain meninges attachment.
    • Middle nasal concha: Structures within the nasal cavity to direct airflow.

Summary Points for Clinical Relevance

  • Hyoid Bone: Unique for not articulating directly with other bones; suspended in soft tissue.
  • Knowledge of foramina: Critical for understanding which nerves/vessels traverse them, relevant for surgical and clinical procedures.
  • Importance of recognizing structures and functions of different cranial bones for anatomy exams or practical assessments.

Practical Information for Exams

  • Emphasis on recognizing and labeling cranial bones, sutures, and foramina.
  • Understanding the significance of each structure and what passes through openings is crucial for both theoretical knowledge and practical applications.