Cranial Anatomy Quiz

The Skull

• The skull encompasses the entire skeletal framework of the head and face, including the mandible.
• The cranium refers to the skull, excluding the mandible.
• The calvarium pertains to the skull after the facial bones have been removed.
• The skull comprises numerous irregular and flattened bones joined by immobile sutures, except for the mandible.

Skull Characteristics

• Viewed from the side, the skull appears slightly flattened.
• The skull's upper surface displays a smooth texture.
• From below, the skull's surface exhibits a very uneven appearance.
• Structurally, the skull is oval in shape, wider at the back than the front.
• It's composed of irregular, flat bones.
• The base of the skull is notable for its significant thickness and strength.
• The skull has numerous openings, called foramina. These allow the passage of the spinal cord, cranial nerves, and blood vessels.
• The skull is composed of two layers of compact bones:
  • The outer layer (outer table) is thick and tough.
  • The inner layer (inner table), is thinner and more brittle.
  • A layer of spongy bone, called the diploë, is between these two layers.

Definitions of Terms

• Skull: The entire skeleton of the head and face, encompassing the mandible.
• Cranium: The skull, devoid of the mandible.
• Calvarium: The skull after the facial bones have been removed.

The Different Views of the Skull

• This section discusses variations in observing the skull anatomically, such as views from above (Norma Verticalis), from behind(Norma Occipitalis), and from the front (Norma Frontalis), from the side (Norma Lateralis) and from the base (Norma Basalis), both internally (Norma Basalis Interna) and externally (Norma Basalis Externa. ).

Cavities of the Skull

• The skull encloses several cavities:
  • Cranial Cavity: Houses the brain.
  • Orbital Cavities: Contain the eyeballs, lacrimal gland, muscles and nerves for eye movement and the blood supply for the eyes.
  • Nasal Cavities: Separated by a bony nasal septum.

Divisions of the Skull Bones

• Cranial Bones (8): These constitute the braincase.

  • Unpaired: Occipital, frontal, sphenoid, ethmoid.
  • Paired: Parietal, temporal.

• Facial Bones (14): Form the midface and surrounding structures.

  • Paired: Nasal, lacrimal, maxilla, zygomatic, palatine, inferior nasal conchae.
  • Unpaired: Vomer, mandible.

Specific Bones and their Functions

• Occipital Bone: Forms the posterior and inferior portions of the cranium. Articular with the parietal bones to form the lambdoid suture.
• Frontal Bone: Forms the forehead and superior parts of the eye sockets.
• Sphenoid Bone: Forms part of the floor of the cranium and acts as a bridge between cranial and facial bones, supporting the sides of the skull.
• Ethmoid Bone: A constituent part of the cranial floor; it's important in composing the medial surface of the eye socket and also forms the roof and sides of the nasal cavity.
• Parietal Bones: Form the roof and upper walls of the cranium. They are situated posterior to the frontal bone and anterior to the occipital bone, articulating to form the sagittal suture.
• Temporal Bones: Located beneath the parietal bones, contributing to the cranium's sides and base. Involved in forming the squamosal suture with the parietal bone.
• Nasal Bones: Form the bridge of the nose and lie between the orbits. Articulate with frontal and maxillary bones.
• Lacrimal Bones: Located within the medial walls of the eye sockets (orbits). Articulate with frontal, ethmoid, and maxillary bones.
• Maxillary Bones: Contribute to the midface. They incorporate the maxillary sinuses and the upper teeth, articulate with almost all other facial bones except the mandible.
• Zygomatic Bones: Part of the facial structure, known as the cheek bones or malar bones. They articulate with the frontal and maxillary bones to form the lateral eye socket wall.
• Palatine Bones: On the posterior section of the hard palate; they communicate with the orbits and create the palate floor.
• Inferior Nasal Conchae: Project from the lateral nasal cavity walls.
• Vomer: A flat bone forming the lower part of the bony nasal septum.
• Mandible: The lower jawbone.

Fontanels

• Membrane-filled spaces between the bones of the fetal skull, crucial for brain growth and allowing the skull to compress during childbirth.

• Closing of fontanels signals complete bone ossification.

• Non-closure indicates incomplete bone development.

• Anterior Fontanel: Located between the frontal and parietal bones. The largest fontanel, it usually closes by age 2.

• Posterior Fontanel: Small, triangular-shaped, situated between the occipital and parietal bones. It typically closes within 2 months of birth.

• Sagittal Fontanel: Located on the sagittal suture. It's smaller than the others, and it may close before birth or by the early months of life.

• Anterolateral (Sphenoidal) Fontanel: Located between parietal, frontal, and sphenoid bones. It closes within 3 months of birth.

• Posterolateral (Mastoidal) Fontanel: Located at the junction of the parietal and occipital bones. It closes within the first year.

Sutures

• Joints between cranial bones.
  • Coronal Suture: Unites the frontal and parietal bones.
  • Sagittal Suture: Joins the two parietal bones.
  • Lambdoid Suture: Connects the parietal and occipital bones.

Classification of Sutures

• TRUE (Vera): Smooth articulating surfaces. Ex: sagittal, coronal sutures. Subcategories:
  • DENTATE: Tooth-like edges.
  • SERRATE: Saw-toothed edges.
  • SCHAMOID: Scale-like.
• FALSE (Notha): Rough articulating surfaces. Ex: Squamosal or harmonia.

Wormian Bones

• Small, extra bones found within the cranial sutures.
• Pneumatic bones contain air spaces.

Skull Anomalies

• Microcephaly: Small skull size due to early fontanel closure.
• Macrocephaly: Large skull size due to late fontanel closure.
• Hydrocephalus: Excessive cerebrospinal fluid causing increased intracranial pressure and potentially open fontanels