Human Anatomy
Cranial Cavity
Cranial cavity anatomy for MBBS: three cranial fossae, dura mater and its folds, dural venous sinuses, cavernous sinus and intracranial haemorrhage, mapped to NMC codes AN30.1 to AN30.5.
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Cranial Cavity
Cranial cavity anatomy for MBBS: three cranial fossae, dura mater and its folds, dural venous sinuses, cavernous sinus and intracranial haemorrhage, mapped to NMC codes AN30.1 to AN30.5.
The cranial cavity chapter maps the floor of the skull into three fossae and traces the dura mater, its folds and the venous sinuses it contains. It underpins the anatomy of intracranial haemorrhage, cavernous sinus lesions and the pattern of nerve exit from the skull base.
High-yield: Cranial Cavity
- The interior of the skull base is divided into anterior, middle and posterior cranial fossae, each lodging a specific part of the brain.
- The anterior cranial fossa holds the frontal lobes and the cribriform plate of the ethmoid, which transmits the olfactory nerves.
- The middle cranial fossa holds the temporal lobes and the pituitary gland in the hypophyseal fossa of the sphenoid.
- The posterior cranial fossa holds the cerebellum, pons and medulla, with the foramen magnum in its floor.
- The dura mater has two layers, an outer endosteal layer and an inner meningeal layer, which separate to form the venous sinuses.
- Folds of dura include the falx cerebri, tentorium cerebelli, falx cerebelli and diaphragma sellae.
- The middle meningeal artery runs in the floor of the middle cranial fossa and, when torn, causes an extradural haemorrhage.
- The cavernous sinus lies on either side of the pituitary and contains the internal carotid artery and the abducent nerve within it.
- The oculomotor, trochlear, ophthalmic and maxillary nerves lie in the lateral wall of the cavernous sinus.
- The superior sagittal sinus lies in the upper margin of the falx cerebri and drains into the confluence of sinuses.
- Cerebrospinal fluid is returned to the superior sagittal sinus through the arachnoid granulations.
- The trigeminal ganglion sits in the trigeminal cave, a dural pocket on the petrous temporal bone.
- Cranial nerves leave the posterior fossa through the internal acoustic meatus, jugular foramen and hypoglossal canal.
- A rise in intracranial pressure can force the uncus through the tentorial notch, compressing the oculomotor nerve and midbrain.
The three cranial fossae
- **Anterior fossa:** Frontal lobes and olfactory bulbs. Cribriform plate transmits the olfactory nerves.
- **Middle fossa:** Temporal lobes and pituitary. Contains cavernous sinus and passages such as the superior orbital fissure and foramina rotundum, ovale and spinosum.
- **Posterior fossa:** Cerebellum, pons and medulla. Contains the foramen magnum, internal acoustic meatus and jugular foramen.
- **Cavernous sinus:** Internal carotid artery and abducent nerve inside; oculomotor, trochlear, ophthalmic and maxillary nerves in the lateral wall.
NMC competencies in this chapter
- **AN30.1:** Features of the anterior, middle and posterior cranial fossae
- **AN30.2:** Dura mater and its folds and dural venous sinuses
- **AN30.3:** Cavernous sinus: relations, contents and communications
- **AN30.4:** Extradural, subdural and subarachnoid haemorrhage
- **AN30.5:** Applied anatomy of the cranial cavity
Frequently Asked Questions
Which structures pass through the cavernous sinus?
The internal carotid artery and the abducent nerve run inside the sinus, while the oculomotor, trochlear, ophthalmic and maxillary nerves lie in its lateral wall.
What causes an extradural haemorrhage?
Tearing of the middle meningeal artery, usually after a blow at the pterion, lets blood collect between the skull and the dura, giving the classic lucid interval followed by deterioration.
Why is the tentorial notch important?
Raised intracranial pressure can herniate the uncus through the notch and compress the oculomotor nerve and midbrain, producing a fixed dilated pupil on the same side.
How does this chapter help in NEET-PG?
Skull base foramina, dural sinuses and herniation syndromes are core neurology and neurosurgery topics, so the cranial cavity is high-yield well beyond first year.
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