In-Depth Notes on Skull Anatomy and Function

Overview of the Skull and Its Components

  • The skull is the foremost complex structure of the axial skeleton comprised of 22 bones:

    • 8 Cranial Bones: Protect the brain and form the cranium.

    • 14 Facial Bones: Shape the face.

Cranial Bones

  1. Frontal Bone:

    • Located at the front (anterior) of the skull.

  2. Parietal Bones (2):

    • Superior sides of the skull.

  3. Occipital Bone:

    • Triangular-shaped, posterior part of the skull.

  4. Temporal Bones (2):

    • Lateral sides, one on each side of the skull.

  5. Sphenoid Bone:

    • Mostly located internally, visible in the cranial cavity.

  6. Ethmoid Bone:

    • Hard to see from outside, significant interiorily.

Facial Bones

  1. Vomer:

    • Forms part of the nasal cavity.

  2. Nasal Bones (2):

    • Form the bridge of the nose.

  3. Maxillae (2):

    • Upper jaw bones.

  4. Mandible:

    • Lower jaw bone, only movable skull bone.

  5. Zygomatic Bones (2):

    • Cheekbones.

  6. Lacrimal Bones (2):

    • Small bones forming part of the eye socket.

  7. Palatine Bone:

    • Located at the roof of the mouth.

  8. Inferior Nasal Conchae (2):

    • Form part of the lateral walls of the nasal cavity.

Sutures of the Skull

  • Sagittal Suture: Between left/right parietal bones.

  • Coronal Suture: Between parietal bones and frontal bone.

  • Lambdoidal Suture: Between parietal and occipital bones.

  • Squamosal Suture: Between parietal and temporal bones.

Cavities of the Skull

  • Cranial Cavity: Protects and houses the brain. Contains the anterior, middle, and posterior cranial fossae:

    • Anterior Cranial Fossa: Houses frontal lobe.

    • Middle Cranial Fossa: Houses temporal lobe.

    • Posterior Cranial Fossa: Houses cerebellum and contains foramen magnum (spinal cord exit).

  • Paranasal Sinuses: Air-filled chambers that lighten skull weight and affect voice resonance:

    • Frontal Sinuses: Above the eyes in the frontal bone.

    • Ethmoidal Sinuses: Within the ethmoid bone.

    • Maxillary Sinuses: Largest, located in the maxilla.

    • Sphenoidal Sinuses: Located within the sphenoid bone.

  • Nasal Cavity: Enclosed by various bones, including the maxilla and ethmoid bone.

  • Orbital Complex: Encompasses bones surrounding the eye sockets.

Unique Structures and Terms

  • Zygomatic Arch: Formed by the zygomatic and temporal bones.

  • Hard Palate: Formed by the maxilla and palatine bones.

  • Nasal Septum: Composed of vomer and ethmoid bone, can be deviated.

  • Deviated Septum: May cause nasal obstruction.

  • Hyoid Bone: A unique bone that supports the tongue, not articulating with any other bone.

Articulations and Joints in the Skull

  • Gomphosis: Joint where teeth fit into the mandible/maxilla.

  • TMJ (Temporomandibular Joint): Only mobile joint in skull, involves the mandibular condyle and temporal bone, allowing for hinge/gliding motion.

Developmental Notes

  • Fontanelles: Soft spots in infant skull that allow for brain growth and easier delivery; named based on locations (anterior, posterior, mastoid, sphenoidal).

  • Craniosynostosis: Premature closure of sutures can affect skull shape, corrected surgically.

Muscles Associated with the Skull

  • Muscles of Mastication: Involved in chewing:

    • Temporalis: Elevates and retracts the mandible.

    • Masseter: Elevates and protracts the mandible.

  • Facial Muscles: Enable facial expressions:

    • Orbicularis Oculi: Closes the eyes.

    • Orbicularis Oris: Puckers lips.

    • Buccinator: Holds food in place during chewing.

  • Sternocleidomastoid: Flexes and rotates the neck; innervated by accessory nerve (Cranial Nerve XI).

  • Splenius Capitis and Cervicis: Extend and rotate the neck; innervated by cervical spinal nerves.

Additional Developmental Concepts

  • Diphodonts: Mammals with two sets of teeth (primary and permanent).

  • Polyphyodonts: Continuous teeth replacement in some animals (e.g., alligators).

  • TMJ Dysfunction: May arise from jaw misalignment, resulting in popping, pain, and other symptoms.

Summary

  • The skull is a complex structure with significant roles in protection and articulation. Understanding the bones, cavities, and joints along with their associated muscles aids in grasping the functional anatomy of the head.