Skull Anatomy Study Notes

Skull Anatomy: Anterior, Lateral, and Posterior Surfaces

Presented by Dr. Shavan Mohammed

Anatomical Markings

  • Fissure: A narrow opening that allows for the passage of nerves and vessels.

  • Foramen (Foramina): A hole or an opening.

  • Fossa (Fossae): A shallow depression.

  • Sulcus (Sulci) or Groove: A narrow depression.

  • Meatus: A tube-like passageway.

  • Condyle: A large rounded prominence.

  • Facet: A smooth flat surface.

  • Head: A rounded articular projection.

  • Crest: A prominent ridge or border.

  • Tubercle: A small rounded process.

  • Linea: A line that is less prominent than a crest.

  • Tuberosity: Not defined in the transcript but suggests a bony prominence or large rounded process.

Fissures and Sulci in Connection to the Skull

  • Suprasylvian Fissure: A notable lateral fissure.

  • Greater Tubercle and Lesser Tubercle: Located within the anatomy of the humerus (context not specified).

  • Intertubercular Sulcus: A groove between the tubercles.

  • Rhinal Fissure: Mentioned but not defined further.

  • Pedicle: Connective anatomical structure noted in context to adjacent features.

  • Sulcus for Spinal Nerve: Specific sulcus designation for spinal nerve pathways.

  • Cervical Vertebrae (C3-C6): Identified with notable anatomical features such as the body, transverse processes, foramen, facets, and bifid spinous processes.

Bones of the Skull

Composition and Structure

  • The skull is composed of several bones that are interconnected by immobile joints known as sutures.

  • Sutures: Composed of connective tissue called sutural ligaments.

  • Mandible: Exception to the immobile nature of sutures, as it connects to the skull via the temporomandibular joint (TMJ).

  • Composition Details:

    • External and internal tables (external & internal laminae) composed of compact bone.

    • Cancellous Spongy Bone: Referred to as Diploë, situated between the two layers of compact bone.

    • Periosteum Coverage: Two layers — outer (pericranium) and inner (endocranium).

Classification of Skull Bones

Cranial Bones

  • Function: Protect the brain.

  • Divisions:

    • Vault: Upper portion of the cranium.

    • Base: Lowest portion of the cranium.

  • Cranial Bones Include:

    1. Frontal

    2. Parietal (paired)

    3. Occipital

    4. Temporal (paired)

    5. Sphenoid

    6. Ethmoid

  • Paired bones are the temporal and parietal, while frontal, occipital, sphenoid, and ethmoid bones are singular.

Facial Bones

  • Function: Support facial soft tissues and contribute to facial appearance.

  • Facial Bones Include:

    1. Zygomatic

    2. Maxilla

    3. Nasal

    4. Lacrimal

    5. Vomer (single)

    6. Palatine

    7. Inferior concha

    8. Mandible (single)

  • Notably, most are paired except for the vomer and mandible.

Anterior View of the Skull

Frontal Bone

  • Forms the upper margin and roof of the orbit.

  • Superciliary Arches: Located on either side of the midline; relate to the frontal process of the maxilla and nasal bones.

  • Articulations:

    • Medially: With the frontal process of maxilla and nasal bones.

    • Laterally: With the frontal process of the zygomatic bone.

  • Supraorbital Foramen (or Notch): Small hole facilitating the passage of supraorbital blood vessels and nerves.

  • Contains two Frontal Air Sinuses.

Nasal Bones

  • Form the bridge of the nose and articulate with each other at the internasal suture.

  • Their lower border joins with the maxillae to create the anterior nasal aperture.

  • Nasal Septum: Divides the nasal cavity into two compartments.

  • Conchae:

    • Superior and Middle Conchae: Projections from the ethmoid bone.

    • Inferior Conchae: Independent bone structures.

Maxillae

  • Comprise several functions:

    1. Form the upper jaw.

    2. Constitute the anterior part of the hard palate.

    3. Form the lateral walls of the nasal cavity.

    4. Shape part of the medial wall and floor of the orbits.

  • Intermaxillary Suture: The junction of the two bones at the midline.

  • Infraorbital Foramen: Located below each orbit, for blood vessels and nerves.

  • Alveolar Processes: Form the alveolar arch that holds the upper teeth.

  • Palatine Processes: Horizontal extensions forming the anterior 2/3 of the hard palate.

  • Contain Maxillary Sinus: Communicates with the nasal cavity, serving as a resonator for voice.

Zygomatic Bone

  • Forms the prominence of the cheek and contributes to the lateral wall and floor of the orbit.

  • Articulations:

    • Medially: With the maxilla.

    • Laterally: With the zygomatic process of the temporal bone to create the zygomatic arch.

  • Contains foramina for the zygomaticofacial and zygomaticotemporal nerves.

  • Mandible Structure: Comprises the horizontal body and two vertical rami meeting at the angle of the mandible.

Lateral View of the Skull

Frontal Bone

  • Forms the anterior section of the skull, articulating with two parietal bones at the coronal suture.

Parietal Bones

  • Construct the roof and sides of the cranium; they meet at midline via the sagittal suture and with the occipital bone at the lambdoid suture.

  • The Vertex: Identified as the highest point on the skull within the sagittal plane.

Fontanelles

  • Anterior (Frontal) Fontanelle: Situated between the frontal bone and the parietal bones; closes around 18 months of age.

  • Posterior (Occipital) Fontanelle: Located between the occipital bone and the parietal bones; closes by the end of the first year of life.

Temporal Bone

Structure and Function

  • Connects with the mandible via the temporomandibular joint (TMJ).

  • Consists of the following parts:

    • Squamous Part: Flat section forming the anterior and superior part of the temple.

    • Tympanic Part: Associated with the ear canal.

    • Mastoid Process: A prominent bony feature behind the external auditory meatus.

    • Styloid Process: Serves as an attachment point for muscles and ligaments.

    • Zygomatic Process: Contributes to the formation of the cheek structure.

  • The Petrous Portion: Internal structure containing parts of the inner ear.

Key Features of the Temporal Bone

  • Mandibular Fossa: Socket interfacing between the squama and the petrous portion; articulates with the condyle of the mandible.

  • External Auditory (Acoustic) Meatus: Opening leading to the ear canal.

Pterion

  • The Pterion: Antero-inferior angle of the parietal bone that articulates with the greater wing of the sphenoid.

  • Clinical Significance: This area is clinically important due to its thin structure that permits pass-through of the anterior branch of the middle meningeal vessels. An injury here may result in vascular damage, posing serious health risks.

Posterior View of the Skull

Articulations at the Occipital Bone

  • The posterior parts of the parietal bones connect with the occipital bone at the lambdoid suture.

  • Each occipital block articulates laterally with the temporal bone.

  • External Occipital Protuberance: An elevation on the midline of the occipital bone giving rise to muscle and ligamentous connections.

  • Nuchal Lines: Serve as points of muscle attachment; superior and inferior lines located on either side of the protuberance.

Occipital Bone

  • Articulates with the following bones:

    • Parietal Bones

    • Temporal Bones

    • Sphenoid Bone (anteriorly)

    • First Cervical Vertebra (Atlas - inferiorly)

  • Foramen Magnum: A large anatomical hole facilitating the spinal cord's passage.

Vault of the Skull

Internal Features

  • The internal surface of the vault displays prominent sutures, while a shallow sagittal groove along the midline functions as a repository for the superior sagittal sinus.

  • Granular Pits (Foveolae): Small depressions lodging lateral lacunae and arachnoid granulations (protrusions of arachnoid mater).

  • Narrow pathways emerge for the anterior and posterior divisions of the middle meningeal vessels.

  • Additional anatomical landmarks include the frontal crest and the internal occipital protuberance.