Cranium Lecture Notes

Cranium

  • The cranium houses the brain.
  • The lecture includes an image requiring identification of labeled parts (A, B, C, D, or E).

Frontal Bone

  • Forms the forehead area.
  • Dips into the eye socket (orbit).
  • Contains the supraorbital foramen, a small hole for blood vessels and nerves.

Maxilla

  • Facial bone below the orbits.
  • Contains the infraorbital foramen.

Lateral Aspect of the Skull

  • Composed of the parietal, temporal, and sphenoid bones.
Parietal Bone
  • The largest portion of the lateral skull.
  • There are right and left parietal bones that meet at the top of the skull.
Temporal Bone
  • Contains the external auditory meatus (ear opening).
  • Houses the anatomy of the ear.
  • Articulates with the zygoma (cheekbone) and the mandible (jaw).
  • Forms the temporomandibular joint (TMJ) with the mandible.
Zygoma
  • The cheekbone.
  • Articulates with the temporal bone.
Mandible
  • The jaw.
  • Articulates with the temporal bone to form the TMJ.

Occipital Bone

  • Forms the base of the skull.

Sutures of the Skull

  • Immovable joints formed when skull bones fuse.
  • Spaces in the skull allow for brain growth, and these spaces close up over time becoming immovable joints.
  • Types of sutures:
    • Coronal suture: runs in the coronal plane.
    • Squamous suture: between the temporal and parietal bones.
    • Lambdoidal suture: between the occipital and parietal bones.

Floor of the Skull (Cranial Cavity)

  • The skull cap is removed and the view is looking down into the floor of the skull.
Foramen Magnum
  • A large opening in the occipital bone for the spinal cord to exit the brain.
  • Foramen magnum is Latin for large opening
Sphenoid Bone
  • Resembles a butterfly or bat.
  • Features:
    • Greater wings: extend to the side of the skull.
    • Lesser wings: a fold over piece.
    • Sella turcica: a depression (fossa) that houses the pituitary gland.
    • Foramen rotundum
    • Foramen ovale: oval-shaped opening in the sphenoid bone.
    • Foramen spinosum
Fossa
  • A depression.
  • Types of cranial fossa:
    • Anterior cranial fossa: located in the frontal bone area.
    • Middle cranial fossa: located in the temporal and sphenoid bone area.
    • Posterior cranial fossa: located in the occipital bone area.
Meningeal Vessels
  • Membranes surrounding the brain forming blood vessels
  • Normal to see lines coursing through the skull
Sinuses
  • Openings in cranial bones that connect to the nose, also called paranasal sinuses.
    • Frontal sinus: located in the frontal bone.
    • Sphenoid sinus: located in the sphenoid bone.
    • Maxillary sinus: located in the maxillary bone (facial bone).

Articulations of the Parietal Bone

  • Articulates with the temporal, frontal, occipital, and sphenoid bones.

Sagittal View of Skull

  • The occipital bone forms the base of the skull.
  • The foramen magnum is where the spinal cord descends from the brainstem.
  • The clivus is the basilar portion on the anterior side of the foramen magnum that slopes superiorly up to the sella turcica.
  • The dorsum sella is at the back of the sella turcica, a high back.

Ethmoid Bone

  • Centrally located in the floor of the cranial cavity.
  • The smallest of the cranial bones.
  • Features:
    • Crista galli: projects superiorly; looks like the mast of a sailboat
    • Cribriform plate: located at the base of the crista galli; contains olfactory foramina for the sense of smell.
    • Perpendicular plate: projects downward.

Ethmoid Sinuses (Air Cells)

  • Located in each half of the ethmoid bone, called the lateral mass.
  • Divided into anterior and posterior groups.

Figure 2.17 Key Features

  • Crista galli: candlestand piece that projects superiorly.
  • Cribriform plate: the base of the crista galli.
  • Perpendicular plate: projected downward.
    *Ethmoid sinuses: is medial to each orbit. Dark areas that filled with air.
    *Two large sinuses are in the maxilla: maxillary sinuses part of facial bone.

Bony Nasal Septum

  • Divided by the perpendicular plate into left and right.
  • The septum is incomplete, the facial bone called the vomer completes the septum
  • Septum (s e p t u m) mean a wall.

Bone Structure of the Skull

  • External table: hard bone exterior.
  • Internal table: hard bone interior.
  • Diploë: spongy bone between the two tables, containing marrow for blood cell production.
    • The skull has inner and outer tables called Diploë, d I p l o with e with two dots over the e.

Key Features of the Sphenoid Bone

  • Resembles a butterfly.
  • Houses the pituitary gland.
  • Contains the foramen ovale.
  • Features lesser and greater wings.
  • Features the sella turcica.

Dorsum Sella

  • Located in the back of the sella turcica.
  • Features posterior clinoid processes (two little processes on the dorsum sella).

Superior Orbital Fissure

  • A deep groove (fissure) between the lesser and greater wings of the sphenoid bone.
  • Nerves pass through to move the face and eyes.

Occipital Bone Features

  • Forms the base of the skull.
  • Articulates with the first vertebrae of the neck.
  • Features the foramen magnum.
  • Features the external occipital protuberance (inion) for ligament and tendon attachment.
  • Features the internal occipital protuberance
  • Clivus continues anterior to the foramen magnum and leads to the sphenoid bone.
  • Features the hypoglossal canal (pathway for nerves). The hypo connects to the occipital bone.

Temporal Bone

  • Articulates with the zygoma (cheekbone) and mandible (jaw).
  • Features the zygomatic process, which reaches out to the zygoma.
  • The zygomatic arch is formed by the zygoma and temporal bone.
  • The temporal bone articulates with the mandible creating the temporomandibular joint.
  • Features the mastoid process (bump behind the ear) containing mastoid air cells.
  • Contains anatomy of the ear; the bone here tickens called the petrous (p e t r o u s)portion.
    *The external ear, the external part we can put our finger or a Q-tip.
    *The middle ear: has the smallest bones in the body called ossicles, malleus, incus and stapes,
    *The stapes is about the size of a grain of rice, very tiny.
  • The inner ear, has all the twist and turns of anatomy, the sensory portion.

Inner Ear (Internal Ear / Labyrinth)

  • The inner ear with all the twists and turns is called the labyrinth
  • Referred to as the bony labyrinth.
  • Parts:
    • Vestibule: connects everything in the center.
    • Cochlea: snail-shell structure for transmitting sound.
    • Semicircular canals: three rings for maintaining balance.

Sutures in Children

  • In children, sutures are still separated, forming soft spots called fontanelles.
  • Anterior fontanelle.

Facial Bones

  • Infraorbital foramina are found in the maxilla.
  • The vomer completes the bony nasal septum.
  • The zygoma (cheekbone) connects from the cheek to the temporal bone.
  • The mandible articulates with the temporal bone.