Skull, cranial cavity and dural sinuses

MEDU3300 Human Structure II

Course Information

  • Course: MEDU3300 Human Structure II

  • Faculty: Faculty of Medicine

  • Institution: The Chinese University of Hong Kong

  • Lecture: HUS2-2: Skull, Cranial Cavity and Dural Sinuses

  • Instructor: Dr. Christopher See

Learning Objectives

  • Distinguish between the cranial and facial bones in various views.

  • Compare and contrast the locations and contents of the cranial fossae.

  • Identify and describe important bony landmarks of the skull.

  • Describe the foramina allowing nerves and blood vessels to pass through.

  • Appreciate the importance of cranial sutures.

  • Describe the structure of the temporomandibular joint.

  • Explain the clinical significance of the cavities of the skull.

  • Understand the dural venous sinus system (including common misconceptions).

The Skull (Cranium)

  • The skull provides:

    • Protection for the brain and special sense organs (vision, taste, hearing, balance, smell)

    • Muscle attachment for: head movement, facial expressions, and chewing

    • Teeth rooted in deep sockets within the mandible and maxillary bones

    • Passage for blood vessels and nerves

Bones of the Skull

  • Composition:

    • Total Bones: 22 bones

    • Cranial bones: 8 bones

      • Surround and protect the brain

      • Calvaria: roof of the skull

    • Facial bones: 14 bones

      • Form the face

      • Contain cavities of eyes, nose, and mouth

      • Support the teeth

Types of Cranial Bones

  • Paired Cranial Bones:

    • Parietal

    • Temporal

  • Unpaired Cranial Bones:

    • Frontal

    • Occipital

    • Ethmoid

    • Sphenoid

Cranial Sutures

  • Definition: Immovable fibrous joints joining skull bones together

  • Major sutures include:

    • Coronal Suture

    • Lambdoid Suture

    • Sagittal Suture

  • Bregma: Meeting point of sagittal and coronal sutures

  • Lambda: Meeting point of sagittal and lambdoid sutures

    • Used as reference points for brain surgery

Fontanelles and Sutures

  • Fontanelles:

    • Spaces filled with soft tissues between cranial bones in infants

    • Allow skull growth and flexibility for childbirth

    • Bones fill the space by age 2

  • Sutures in Adults:

    • 10 sutures

Mandible

  • Characteristics:

    • Largest and strongest bone of the face

    • Houses lower teeth

    • Composed of:

    • Horizontal body

    • Two perpendicular rami (with processes)

      • Coronoid process

      • Condylar process

    • Muscle attachments for mastication (chewing)

Temporomandibular Joint (TMJ)

  • The only movable joint in the skull

  • Articulations:

    • Between mandibular fossa of temporal bone and condylar head of mandible

  • Stabilization: ligaments outside the joint capsule

  • Joint divided by a fibrous articular disc into upper and lower parts

Cranial Fossae

  • Composed of three step-like depressions in the skull floor:

    • Anterior Cranial Fossa:

    • Bounded by lesser wings of the sphenoid

    • Middle Cranial Fossa:

    • Bounded by superior aspect of the petrous temporal bone

    • Posterior Cranial Fossa:

    • Extends to the superior aspect of the petrous temporal bone

  • Function: Accommodate the shape of the brain and allow passage for nerves and blood vessels

  • Vulnerability: Fragile and prone to fracture

Foramina in Cranial Fossae

  • Foramina provide critical pathways for nerve and blood vessel passage

  • Highlights include:

    • Ophthalmic Nerve: Supplies sensation to the floor of the posterior cranial fossa

    • Spinal Nerves: Supply the internal surface of the skull and are associated with referred pain

Base of Skull

  • Key components include:

    • Maxilla

    • Hard palate

    • Zygomatic bone

    • Frontal bone

    • Sphenoid bone

    • Occipital bone

    • External occipital protuberance

  • Foramen Magnum: Largest foramen, allowing the spinal cord to exit the cranium

External View of Base of Skull

  • Features:

    • Rough surface for muscle attachment (includes styloid process, mastoid process, lateral and medial pterygoid plates, occipital condyle)

Foramina for Blood Vessels and Cranial Nerves

  • Important foramina include:

    • Foramen magnum

    • Facial nerve pathways

    • Internal carotid artery passage

  • Key nerves:

    • CN V (Trigeminal) and its division

    • CN IX, X, XI

Floor of Cranial Cavity

  • Displaying foramina corresponding to cranial bones and brain functions

  • Major foramina include cribriform foramina, optic canal, superior orbital fissure, foramen rotundum, foramen ovale, etc.

  • Each foramen allows specific nerve pathway or blood vessel passage

Cavities of the Skull

  • Cavities:

    • Surround and protect the brain and sensory organs

    • Types:

    • Cranial cavity

    • Orbital cavity

    • Nasal cavity

    • Oral cavity

    • Tympanic (middle ear) cavity

Orbital Cavity

  • Two bony sockets protecting eyes, connecting with cranial and nasal cavities

Nasal Cavity

  • Part of the respiratory system

  • Formed by cartilage and various bones, divided by a nasal septum

  • Contains nasal turbinates (concha) on the lateral wall

Paranasal Sinuses

  • Four hollow air-filled spaces (frontal, ethmoid, maxillary, sphenoid)

    • Functions include:

    • Decreasing skull weight

    • Shaping the face

    • Enhancing voice resonance

    • Providing buffer against blows

Oral Cavity

  • Composed of the vestibule and oral cavity proper

    • Vestibule: Area between lips/cheeks and teeth

    • Oral Cavity Proper:

    • Roof: hard and soft palate

    • Muscular floor: consists of mylohyoid and geniohyoid muscles

    • Tongue: attached to the floor via frenulum

Tympanic (Middle-ear) Cavity

  • An air-filled space in the temporal bone

    • Contains auditory ossicles: malleus, incus, stapes

    • Connection to the nasal cavity via Eustachian tube for pressure equalization

Clinical Notes on Dural Sinuses and Hemorrhage

  • Intracranial Hemorrhage: Results from bleeding in cranial cavity, leading to increased intracranial pressure

    • Testing for blood in CSF through lumbar puncture

  • Dural Folds: Help partition cranial cavity into compartments; major folds include falx cerebri, tentorium cerebelli, falx cerebelli

  • Dural Venous Sinuses: Lined with endothelium, receive blood from the brain, drain into internal jugular veins (includes superior sagittal sinus, inferior sagittal sinus, straight sinus, etc.)

  • Cavernous Sinus: Receives blood from cerebral and ophthalmic veins; connections can lead to infectious pathways. Vulnerable structures include the internal carotid artery and cranial nerves within the sinus

  • Clinical significance in conditions such as aneurysms, thrombosis, and possible infections leading to meningitis.

Concluding Sections

  • Refer to previous slides for further information and subjects beyond the current material.

  • Resources:

    • Video and audio summaries available on the noted YouTube channel