Skull

1. Overview

The skull is a complex bony structure that forms the head's skeleton. It encases and protects the brain, supports the sensory organs, and forms the framework for the face. The skull is composed of 22 bones, most of which are fused in adults. It is divided anatomically into two main parts: the neurocranium (braincase) and the viscerocranium (facial skeleton).

2. Location

The skull is located at the superior end of the axial skeleton:

• Superior to: The cervical vertebrae (begins at the foramen magnum and sits on the first cervical vertebra, the atlas).

• Anterior to: The vertebral column and posterior neck structures.

• Encases: The brain and forms the upper part of the respiratory and digestive tracts.

3. Structure

The skull is composed of 22 bones, most of which are joined by immovable fibrous joints called sutures:

• Neurocranium (8 bones):

  • Frontal

  • Occipital

  • Two parietal

  • Two temporal

  • Sphenoid

  • Ethmoid

• Viscerocranium (14 bones):

  • Mandible

  • Maxillae (2)

  • Zygomatic (2)

  • Nasal (2)

  • Lacrimal (2)

  • Palatine (2)

  • Inferior nasal conchae (2)

  • Vomer

Other important skull components include:

• Sutures: Coronal, sagittal, lambdoid, and squamous sutures connect cranial bones.

• Foramina: Openings for nerves and blood vessels (e.g., foramen magnum, optic canal, jugular foramen).

• Sinuses: Air-filled cavities in the frontal, sphenoid, ethmoid, and maxillary bones that lighten the skull and enhance voice resonance.

4. Function

The skull performs multiple critical functions:

• Protects the brain: The neurocranium forms a rigid case for the brain and meninges.

• Supports sensory organs: Houses the structures of vision, hearing, balance, smell, and taste.

• Facilitates speech and mastication: Provides the framework for the oral cavity, jaws, and muscles of facial expression.

• Attachment for muscles: Serves as the origin and insertion for muscles involved in head movement, mastication, and facial expression.

5. Physiological role(s)

The skull also plays roles beyond protection and structure:

• Encloses cranial nerves: Contains foramina for the passage of all 12 cranial nerves.

• Hematopoiesis (in infancy): Some cranial bones contain red bone marrow, active in early hematopoiesis.

• Growth and development: Skull growth accommodates rapid brain expansion in infancy and childhood.

• Resonance and phonation: Paranasal sinuses and the oral cavity contribute to voice quality and sound resonance.

6. Clinical Significance

The skull is involved in numerous medical and anatomical conditions:

• Fractures:

  • Can occur from blunt trauma, falls, or accidents; may involve cranial vault or base of skull and risk damage to brain or vessels.

• Craniosynostosis:

  • Premature fusion of sutures in infants, leading to abnormal skull shape and potential intracranial pressure increase.

• Temporomandibular joint (TMJ) dysfunction:

  • Involves the articulation between the temporal bone and mandible; can cause jaw pain, clicking, and difficulty chewing.

• Sinus infections and tumors:

  • Paranasal sinuses may become infected or obstructed; neoplastic growths may affect bone integrity.

• Skull base tumors:

  • Lesions in the cranial base (e.g., meningiomas, chordomas) may compress cranial nerves and brainstem structures.

• Deformities and trauma in childbirth:

  • Fontanelles and sutures allow for flexibility during passage through the birth canal but may be sites of pathology.