Human Anatomy
Osteology of the Skull
Skull osteology for MBBS: vault and base, cranial fossae, foramina and their contents, pterion and fontanelles, mapped to NMC codes AN26.1 to AN26.7.
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Osteology of the Skull
Skull osteology for MBBS: vault and base, cranial fossae, foramina and their contents, pterion and fontanelles, mapped to NMC codes AN26.1 to AN26.7.
This chapter covers the osteology of the skull, its vault and base, the individual bones and the many foramina that transmit nerves and vessels. It emphasises the cranial fossae and their contents, the pterion and extradural haemorrhage, and the fontanelles of the infant skull.
High-yield: Osteology of the Skull
- The skull is divided into the cranium, which houses the brain, and the facial skeleton.
- The calvaria is the vault of the skull and the base is the floor on which the brain rests.
- The pterion is the H-shaped meeting of the frontal, parietal, sphenoid and temporal bones and overlies the middle meningeal artery.
- A blow at the pterion can rupture the middle meningeal artery and cause an extradural haemorrhage.
- The cranial base has three fossae: anterior, middle and posterior, each holding part of the brain.
- The anterior cranial fossa holds the frontal lobes and the cribriform plate transmits the olfactory nerves.
- The middle cranial fossa holds the temporal lobes and the pituitary gland lies in the sella turcica of the sphenoid.
- The posterior cranial fossa holds the cerebellum and brainstem and contains the foramen magnum.
- The foramen magnum transmits the medulla, the vertebral arteries and the spinal roots of the accessory nerves.
- The foramen ovale transmits the mandibular nerve and the foramen spinosum the middle meningeal artery.
- The jugular foramen transmits the internal jugular vein and the ninth, tenth and eleventh cranial nerves.
- The internal acoustic meatus transmits the facial and vestibulocochlear nerves.
- In the newborn the anterior fontanelle closes at about eighteen months and the posterior at about two to three months.
- The mandible is the only movable bone of the skull and articulates at the temporomandibular joint.
Key foramina and their contents
- **Foramen magnum:** Medulla, vertebral arteries, spinal roots of the accessory nerves.
- **Foramen ovale:** Mandibular division of the trigeminal nerve and the accessory meningeal artery.
- **Foramen spinosum:** Middle meningeal artery and the meningeal branch of the mandibular nerve.
- **Jugular foramen:** Internal jugular vein and the glossopharyngeal, vagus and accessory nerves.
NMC competencies in this chapter
- **AN26.1:** Norma verticalis, frontalis, occipitalis and lateralis of the skull
- **AN26.2:** Norma basalis and the base of the skull
- **AN26.3:** Interior of the cranial base and the three cranial fossae
- **AN26.4:** Foramina of the skull and their contents
- **AN26.5:** Individual bones of the skull
- **AN26.6:** Fontanelles and the neonatal skull
- **AN26.7:** Applied anatomy of the skull
Frequently Asked Questions
Why is the pterion clinically important?
The pterion is a thin region where four bones meet and it overlies the anterior branch of the middle meningeal artery. A blow here can fracture the bone and tear the artery, causing an extradural haemorrhage.
What passes through the foramen magnum?
The foramen magnum transmits the lower end of the medulla oblongata, the vertebral arteries, and the spinal roots of the accessory nerves, connecting the cranial cavity with the vertebral canal.
Where does the pituitary gland sit?
The pituitary gland lies in the sella turcica, a saddle-shaped depression on the body of the sphenoid bone in the middle cranial fossa. This bony relation is important in pituitary surgery and tumours.
When do the fontanelles close?
The posterior fontanelle usually closes by about two to three months and the anterior fontanelle by about eighteen months. A tense or sunken anterior fontanelle is a useful clinical sign in infants.
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