Skull Vault, Cranial Cavity and Meninges 4

Question 1

What artery are the vertebral arteries branches of?

Answer 1

They are branches of the subclavian arteries which arise in the root of the neck.

Question 2

Describe the path of the vertebral arteries through the cervical vertebrae?

Answer 2

• each vertebral artery passes through the foramen transversium of the 6th cervical vertebrae (miss out the 7th cervical vertebrae).
• each vertebral artery passes through a series of cervical vertebrae and they pass through each successive foramen transversium.
• the vertebral arteries come to lie on each side of the lateral mass of the atlas.

Question 3

What happens to the vertebral arteries at the atlas vertebrae?

Answer 3

After they come to lie on each side of the lateral mass of the altas vertebra, the vertebral arteries wind around the lateral mass of the atlas vertebrae and pass over the posterior arch of the atlas where it enters the foramen magnum.

Question 4

What happens to the vertebral artery once it enters the foramen magnum?

Answer 4

Once it enters the foramen magnus, it will pierce the dura mater and enter the cranial cavity.

Question 5

How do the 2 vertebral arteries form the basilar artery?

Answer 5

The 2 vertebral arteries run alongside the lateral aspect of the medulla and then fuse with each other in front of the pons to form the basilar artery.

Question 6

What arteries does the vertebral artery give off?

Answer 6

The vertebral artery gives off anterior and posterior spinal arteries which are really important arteries and they are pivotal to the blood supply of the spinal cord.

Question 7

Where does the basilar artery give its branches to?

Answer 7

The basilar artery gives its branches to:

• cerebellum
• pons
• labyrinth
• inner ear

Question 8

What does the basilar artery divide into?

Answer 8

The basilar artery divides into the 2 posterior cerebral arteries.

Question 9

How do the 2 posterior cerebral arteries communicate with the middle cerebral artery?

Answer 9

Via the Circle of willis.

Question 10

What is the significance of the Circle of Willis?

Answer 10

At the circle of willis, we can communication between all of the arteries that supply the cerebrum and this means that we can equalise the blood pressure and also ensures that there is a collateral blood supply in case one artery gets partially or completely blocked.

Question 11

What do the posterior cerebral arteries supply?

Answer 11

The posterior cerebral arteries supply much of the occipital and temporal lobes of the cerebral hemisphere.

Question 12

Where does the interal carotid artery arise?

Answer 12

Arises in the neck at the bifurcation of the common carotid arteries.

Question 13

Does the internal carotid artery have any branches in the neck?

Answer 13

No the internal carotid artery has no branches in the neck.

Question 14

What is the path of the internal carotid artery?

Answer 14

1. passes into carotid canal of petrous temporal bone.
2. turns a right angle
3. travels forwards through the petrous temporal bone to the apex of the petrous temporal bone.
4. at the apex of the petrous temporal bone it is going to run out of the bony carotid canal and across the top of the foramen lacerum
5. when running across the top of the foramen lacerum, turns another right angle
6. rises into the cavernous sinus
7. travels forwards through the cavernous sinus
8. right angle turn to bring the artery through the roof of the cavernous sinus
9. when through the roof of the cavernous sinus it lies medial to the anterior clinoid process
10. turns backwards and upwards by the side of the optic chiasma
11. terminates.

Question 15

What is the foramen lacerum?

Answer 15

This is a cleft between the petrous temporal bone and the sphenoid bone.

In life it is covered with cartilage therefore it can only be seen in a dried skull.

Question 16

At its termination what does the internal carotid artery divide into?

Answer 16

It divides into the anterior and middle cerebral arteries.

Question 17

What does the anterior cerebral artery supply?

Answer 17

Winds around the genu of the corpus callosum so that it can supply the medial and superolateral aspects of the cerebral hemispheres.

Question 18

What does the middle cerebral artery supply?

Answer 18

The middle cerebral artery enters the lateral cerebral sulcus and it gives off important and delicate branches to the internal capsule.

It continues on to supply most of the lateral aspects of the cerebral cortex.

Question 19

Which branch of the internal carotid artery is given off just as it emerges through the roof of the cavernous sinus?

Answer 19

Ophthalmic artery.

Question 20

How does the ophthalmic artery enter the orbit?

Answer 20

The opthalmic artery enters the orbit through the optic foramen below and lateral to the optic nerve.

Question 21

What does the opthalmic artery supply?

Answer 21

• contents of the orbit
• emerges to supply the skin of the forehead and the eyebrow

Question 22

What is the most important branches of the ophthalmic artery? T

Answer 22

The central artery of the retina.

Question 23

Why is the central artery of the retina the most important branch of the opthalmic artery?

Answer 23

Because it is an end artery and it is the sole artery to the retina.

Question 24

How does the central artery of the retina reach the eye?

Answer 24

It runs through the optic nerve to reach the eye.

Question 25

What are the 5 layers of the scalp?

Answer 25

1. S - skin
2. C - dense connective tissue layer
   
   1. skin is firmly attached to this layer
3. A - epicranial aponeurosis
4. L - loose layer of connective tissue
5. P - periosteum that is attached to the bone

Question 26

What is the epicranial aponeurosis attached to?

Answer 26

It is a tough layer that is attached to the front, sides and back to the muscles that move the scalp.

Question 27

Which scalp layer allows free movement of the scalp?

Answer 27

The loose connetive tissue layer beneath.

Question 28

What is the function of the dense connective layer beneath the skin of the scalp?

Answer 28

This layer forms a sound barrier against superficial infections and lacerations.

Question 29

What structures are within the dense connective tissue layer?

Answer 29

We have here the nerves and vessels that run upwards and into the skin.

Question 30

When does a wound to the scalp gape?

Answer 30

Deeper wounds to the scalp usually do not pull apart if the epicranial aponeurosis is intact. However, if deeper wounds do pull apart this is because the muscles that attach to the epicranial aponeurosis pull the aponeurosis in different directions and here, the aponeurosis requires suturing because the wound will gape.

Question 31

Why is it dangerous if blood and infection track into the loose layer of connective tissue beneath the epicranial aponeurosis?

Answer 31

Because emissary veins may facilitate communcation with the underlying intracranial region and the cranial venous sinuses.

Question 32

How does an extradural haemorrhage occur?

Answer 32

It occurs when we have an injury to the cranium that could damage the meningeal arteries and the diploic veins within the vault bones.

Question 33

What are the symptoms of prolonged extradural bleeding?

Answer 33

• compression of the brain
• drowsiness
• eventual loss of consciousness
• the medial part of the temporal lobe could spill over the free edge of the tentorium cereblli on the same side as the lesion
  
  • stretches/ traps the oculomotor nerve (3rd cranial nerve)
  • gradual loss of the parasympathetic supply to the sphincter pupillae will cause the pupil to increasingly dilate and will not respond to light

Question 34

Where does a subdural haemorrhage occur?

Answer 34

Occurs between the dura and the arachnoid.

Question 35

What can cause a subdural haemorrhage?

Answer 35

They could occur after a box or blow to the head which shakes the brain enough to tear the cerebral veins that pass from the brain to the cranial venous sinuses.

They can be acute and sudden or slow and chronic.

Question 36

How can we get a subdural haemotoma or clot and what are its repercussions?

Answer 36

A slow and chronic subdural bleed can spread and localise to form a subdural haemotoma.

Blood clots draw in fluid and then they expand so that the symptoms of a subdural bleed might not actually appear for up to weeks after the initial incident.

Question 37

What is a subarachnoid haemorrhage?

Answer 37

This is sudden and can be mistaken by the patient for a blow to the head.

They can be very painful because of the immediate meningeal irritation that occurs.

Question 38

What is a common cause of a subarachnoid haemorrhage?

Answer 38

A rupture of a so called berry aneurysm.

Question 39

What is a berry aneurysm?

Answer 39

These are thin walled outpouchings from the large arteries that supply the brain and they eventually become prone to rupture under continued arterial pressure.

This is a common cause of a stroke.

Question 40

In what groups are bleeds in the brain/ strokes more common?

Answer 40

In old age or hypertension.

Question 41

Which artery is a classic site of stroke?

Answer 41

The middle cerebral arery.

Question 42

What happens if there is a stroke in the middle cerebral artery?

Answer 42

Bleeding into the internal capsule of the brain from small frail branches of the middle cerebral artery paralyses the motor nerve fibres that are travelling from the cerebral cortex to the brain stem and spinal cord.

As a result, the patient will get hemiplegia and loss of speech which may or may not resolve.