Skull Vault, Cranial Cavity and Meninges 2

Question 1

Describe the appearance of the sphenoid bone behind the anterior cranial fossa.

Answer 1

The central part of the body of the sphenoid is raised high in the midline behind the anterior cranial fossa.

Question 2

What part of the sphenoid bone houses the pituitary gland?

Answer 2

There is a part of the sphenoid bone that presents with a depression in the midline which houses the pituitary gland in life. This is called the pituitary fossa but it also referred to as the selca turcica.

Question 3

What does the pituitary fossa have at its corners?

Answer 3

It has 2 anterior clinoid processes and 2 posterior clinoid processes.

Question 4

Where are the optic foramina?

Answer 4

These are 2 important passageways in the lesser wing of the sphenoid bone lead through to the orbital cavities.

Question 5

What goes through the optic foramina?

Answer 5

The optic foramina transmit optic nerves to the eye.

Question 6

What is the name of the fissure lateral to the optic foramina?

Answer 6

We have the superior orbital fissure.

Question 7

What does the superior orbital fissure lead to?

Answer 7

It leads to the orbital cavity.

Question 8

Where is the foramen rotundum?

Answer 8

This is beneath the superior orbital fissure, close to the body of the sphenoid bone, we have this round foramen called the foramen rotundum.

Question 9

Where does the foramen rotundum lead to?

Answer 9

It leads to the cheeks.

Question 10

Other than the foramen rotundum and the optic foramina what are the other 2 foramina in the middle cranial fossa?

Answer 10

Foramen ovale and foramen spinosum.

Question 11

What is the path of the foramen ovale and the foramen spinosum?

Answer 11

They pass through the greater wing of the sphenoid bone and through the cranial base.

Question 12

Out of the foramen ovale and the foramen spinosum which one is the most prominent?

Answer 12

The foramen ovale is more prominent

Question 13

Where is the foramen spinosum?

Answer 13

The foramen spinosum is lateral to the foramen ovale in a part of the greater wing of the sphenoid called the spine of the sphenoid.

Question 14

What do the superior orbital fissure, foramen rotundum and foramen ovale all transmit?

Answer 14

They all transmit a large division of the trigeminal nerve which is the 5th cranial nerve.

Question 15

What does the foramen spinosum transmit?

Answer 15

It transmits an artery called the middle meningeal artery.

This artery creates a deep groove in the bone along its course over the floor of the middle cranial fossa and even more of a groove on the inner aspect of the side wall of the cranial vault.

Question 16

Why is the middle meningeal artery important?

Answer 16

It is primarily a nutrient artery to the bones of the cranial vault.

Question 17

Other than the sphenoid bone, what other bones make up the middle cranial fossa?

Answer 17

The 2 temporal bones on the left and the right.

Question 18

What are the 2 parts of the temporal bone?

Answer 18

We have a petrous part which is the thick portion and a temporal part which is the thin portion.

Question 19

Describe the petrous part of the temporal bone.

Answer 19

This projects like a pyramid across the middle cranial fossa and is thick and hard.

The petrous part has a superior margin that forms a thick bony ridge that runs obliquely forwards across the cranial cavity towards the body of the sphenoid bone.

Question 20

Describe the squamous temporal bone.

Answer 20

This is the flat and thin portion and it forms part of the side wall of the middle cranial fossa and the cranial vault.

Question 21

Why is the petrous crest significant?

Answer 21

The petrous crest is at the top edge of the petrous bone and it forms the boundary between the middle and posterior cranial fossa.

Question 22

What is present within the substance of the petrous bone?

Answer 22

The organs of hearing and balance.

Question 23

What forms the anterior aspect of the posterior cranial fossa?

Answer 23

The vertically orientated posterior aspect of the petrous temporal bone.

Question 24

What is the internal acoustic meatus?

Answer 24

This is a prominent foramen in the posterior aspect of the petrous temporal bone which transmits the nerves to the organs of hearing and balance as well as the nerves that are destined to supply the muscles of the face.

Question 25

Apart from the petrous temporal bone, what else forms the posterior cranial fossa?

Answer 25

Further back, the occipital bone forms the posterior cranial fossa.

Question 26

What is the jugular foramen?

Answer 26

This is a rather irregular hole between the petrous temporal bone and the occipital bon. It is really a space between 2 bones as opposed to being a foramen through 1 bone.

Question 27

What does the jugular foramen transmits?

Answer 27

It transmits 3 cranial nerves and a large vein called the internal jugular vein.

Question 28

What is the function of the internal jugular vein?

Answer 28

It returns blood from the brain to the neck and the thorax.

Question 29

What dominates the posterior cranial fossa?

Answer 29

The foramen magnum.

Question 30

What 2 structures are continuous through the foramen magnum?

Answer 30

The spinal cord and the medulla.

Question 31

What is the hypoglossal canal?

Answer 31

This is a canal that runs above the occipital condyle and transmits the hypoglossal nerve which is the 12 cranial nerve out of the posterior cranial fossa.

Question 32

What are the blood vessels in the diploe called?

Answer 32

They are called diploic veins. They look like spiders in the parietal region therefore here they are called parietal spiders.

Question 33

What are the brain and spinal cord covered by?

Answer 33

They are covered by 3 layers of meninges called the dura mater, arachnoid mater and pia mater.

Question 34

Where are the cranial meninges and spinal meninges continous with each other?

Answer 34

They are continuous through the foramen magnum.

Question 35

What does the cranial dura do that the spinal dura doesnt do?

Answer 35

The cranial dura fuses with the periosteum of the internal surface of the vault whenever it is directly in contact with it.

The fusion of the dura and periosteum takes place over wide areas inside the skull so that when the skull cap is removed the underlying periosteum often strips off the bone as well and it remains fused with the outer surface of the dura.

Question 36

Describe the dura.

Answer 36

It is a tough collagenous membrane.

Question 37

Where does the middle meningeal artery lie in relation to the dura and what is its function?

Answer 37

The middle meningeal artery ascends into the skull through the foramen spinosum and it supplies a little bit of blood to the dura but its main function is to be the nutrient artery to the bones of the skull.

The middle meningeal artery sits outside the dura and it has to pierce the periosteum to enter the bones of the skull therefore we say that it is extradural.

Question 38

Is the fusion of the dura and the periosteum that lines the interior of the skull complete?

Answer 38

No - in some places the dura forms folds which pass to the interior of the cranial cavity in the form of the fibrous septa that are between parts of the brain. In other places, there are long gaps between the dura and the periosteum in the form of channels or sinuses and these carry venous blood.

Question 39

What is the falx cerebri?

Answer 39

The dura lining the vault of the skull is reflected into the cranial cavity between the 2 cerebral hemispheres as a sickle shaped fold which is the falx cerebri.

Question 40

What is the falx cerebri attached to anteriorly?

Answer 40

It is attached to the crista galli.

Crista galli is the small crest of bone that projects upwards in the midline from the ethmoid bone in the anterior cranial fossa.

Question 41

What happens to the falx cerebri at the posterior end?

Answer 41

It spreads into a horizontal fold of dura that is called the tentorium cerebelli.

Question 42

What is the function of the tentorium cerebelli?

Answer 42

It supports the cerebral hemispheres above and forms a tented roof over the posterior cranial fossa below. The slope of the tentorium deflects the weight of the cerebral hemispheres to the parietal bones which form the walls of the cranial cavity here.

Question 43

What is the path of the outer margin of the tentorium cerebelli?

Answer 43

It runs forwards around the rim of the petrous temporal bones and as far as the sides of the pituitary fossa in front.

Question 44

Describe the inner margin of the tentorium.

Answer 44

It is crescentic and free.

Question 45

What passageway does the brainstem pass through?

Answer 45

It passes through a passageway that is bounded by the body of the sphenoid in front and the free edge or border of the tentorium behind.

Question 46

What structures does the brainstem connect?

Answer 46

The brainstem connects the cerebral hemispheres above to the midbrain and pons below.

Question 47

Where do the inner free borders of the tentorium attach?

Answer 47

They sweep anteriorly on each side to attach to the anterior clinoid processes

Question 48

What happens to the outer rim of the tentorium that attaches to the petrous crest?

Answer 48

It runs into the petroclinoid ligament anteriorly.

The petroclinoid ligament joins the apex of the petrous temporal bone to the posterior clinoid process.

Question 49

Where do the venous sinuses drain blood from?

Answer 49

They drain blood from brain, meninges and skull mainly into the internal jugular vein.

Remember that the interal jugular vein leaves the skull through the jugular foramen

Question 50

What are some of the small venous sinuses continuous with through the foramen magnum?

Answer 50

They are continuous with the vertebral venous plexuses around the spinal cord.