Cranium Anatomy Notes

Cranium Anatomy Notes

Key Components of the Cranium

  • Cranium: Composed of two main parts: Neurocranium and Viscerocranium
    • Neurocranium: 8 bones that encase the brain
    • Pneumatized Bones: These may contain air-filled cavities to lighten the skull structure (e.g., frontal, temporal, sphenoid, ethmoid).
    • Calvaria (Skullcap): The dome-like roof of the skull.
    • Cranial Base (Basicranium): The bottom portion of the skull where it interfaces with the spine.
    • Viscerocranium: 15 irregular bones that comprise the facial skeleton.
    • Includes bones of the frontal region, orbits, nasal region, maxillae, and mandible.

Neurocranium Structures

  • Major Bones:

    • Frontal bone
    • Parietal bones (2)
    • Temporal bones (2)
    • Occipital bone
    • Sphenoid bone
    • Ethmoid bone

  • Cranial Sutures:

    • Coronal Suture: Joins the frontal bone to the parietal bones.
    • Sagittal Suture: Joins the two parietal bones.
    • Lambdoid Suture: Joins the parietal bones to the occipital bone.

  • Prominent Anatomical Features:

    • Glabella: Smooth area between the eyes just above the nose.
    • Nasion: Bridge of the nose area.
    • External Occipital Protuberance (Inion): Bump on the back of the skull.

Viscerocranium Structures

  • Major Bones:

    • Nasal bones (2)
    • Maxillae (2)
    • Zygomatic bones (2)
    • Mandible
    • Inferior nasal conchae (2)
    • Vomer

  • Features of the Mandible:

    • Mental Protuberance: Pointed extension of the chin.
    • Mental Foramen: Opening for nerves and vessels.
    • Coronoid Process: For muscle attachment.
    • Condyloid Process: Forms the joint with the skull.

Brain and Meninges

  • Meningeal Layers:

    • Narrows membranes surrounding the brain; includes:
    • Dura Mater: Tough outer layer with two layers (periosteal and meningeal).
    • Arachnoid Mater: Middle layer with subarachnoid space containing cerebrospinal fluid (CSF).
    • Pia Mater: Thin layer directly covering the brain.

  • Dural Infoldings:

    • Falx Cerebri: Separates the two cerebral hemispheres.
    • Tentorium Cerebelli: Separates cerebrum from cerebellum.
    • Diaphragma Sellae: Covers the sella turcica where the pituitary gland resides.

Cranial Foramina and Their Contents

  • Foramina: Openings that allow nerves and blood vessels to pass through.
    • Optic Canal: Transmits optic nerve.
    • Foramen Rotundum: Transmits maxillary nerve (V2).
    • Foramen Ovale: Transmits mandibular nerve (V3).
    • Foramen Magnum: Allows the spinal cord to connect with the brain.
    • Internal Acoustic Meatus: Transmits the facial and vestibulocochlear nerves.

Skull and Brain Connections

  • Cranial Nerves: The skull houses several cranial nerves where:

    • CN I (Olfactory) arises from the frontal lobe.
    • CN II (Optic) passes through the optic canal.
    • CN V (Trigeminal) branches from the pons).

  • Blood Supply:

    • Primarily from the internal carotid artery, which branches into anterior and middle cerebral arteries.
    • Venous return through the internal jugular vein.

Muscles Associated with the Skull and Face

  • Muscles of Facial Expression:

    • Occipitofrontalis: Raises eyebrows.
    • Orbicularis Oculi: Closes eyelids.
    • Buccinator: Presses cheeks against molars.
    • Zygomaticus Major: Elevates corner of the mouth (smiling).

  • Innervation:

    • All facial muscles are innervated by the facial nerve (CN VII).