L10 Meninges, Ventricles and Blood Supply to the Brain

Question 1

What are the meninges?

Answer 1

The membranes surrounding the CNS (brain and spinal cord).

Question 2

What are the 3 meninges?

Answer 2

• Dural layer
• Arachnoid layer
• Pia

Question 3

Describe the dura mater of the brain.

Answer 3

• Thick tissue
• Also called principal layer
• Provides some protection to the brain

Question 4

Describe the arachnoid mater of the brain.

Answer 4

• Thin, fibrous cellular layer
• Has arachnoid trabeculae which provide structure to the subarachnoid space and keep the layer apart from the pia layer
• Has arachnoid granulations which project through the dural layer, form one way valves into the venous sinuses

Question 5

Describe the pia mater of the brain.

Answer 5

• Thin membrane
• Directly above the brain tissue
• Permeable to CSF

Question 6

What is the outer dural layer?

Answer 6

The periosteum of the skull.

Question 7

What is the membrane where the dural layers of the left and right hemispheres meet called?

Answer 7

The falx cerebri: a vertical sheet of dura seperating the hemispheres.

Question 8

What is present where the dural layer and periosteum seperate superiorly?

Answer 8

The superior sagittal (venous) sinus

Question 9

What is found in the subarachnoid space?

Answer 9

CSF and small veins and capillaries.

Question 10

Which artery supplies blood to the superior surface of the dura?

Answer 10

Middle meningeal artery.

Question 11

Which horizontal sheet of dura seperates the occipital cortex and cerebellum?

Answer 11

The tentorium cerebelli.

Question 12

What are the 3 spinal cord meninges?

Answer 12

• Dural layer: outer meningeal layer covering spinal cord, ventral and dorsal roots
• Arachnoid layer: middle meningeal layer
• Pia mater: inner meningeal layer

Question 13

What space is between the dural and arachnoid spinal meningeal layers?

Answer 13

Subdural space

Question 14

What space is between the arachnoid and pia spinal meningeal layers?

Answer 14

Subarachnoid space

Question 15

What are the denticulate ligaments?

Answer 15

Bilateral extensions of pia mater connecting to arachnoid and dural layers to provide some stability to the spinal cord.

Question 16

What is the ventricular system of the brain?

Answer 16

A communicating network of cavities in the brain filled with CSF.
The ventricles synthesise and store CSF.

Question 17

What are the cavities of the ventricular system?

Answer 17

• 2 lateral ventricles joined at the midline via the intraventricular foramen
• The third ventricle running through the midline
• The cerebral aquaduct at the base of the thrid ventricle (connects 3rd and 4th)
• The fourth ventricle, continous with the central canal which runs the full length of the spinal cord

Question 18

Where does CSF enter the subarachnoid space of the brain and spinal cord?

Answer 18

Enters via the median and lateral apertures of the fourth ventricle.

Question 19

Which tissue synthesises CSF?

Answer 19

The choroid plexus: found in the ventricle roofs, secretes 500ml of CSF each day

Question 20

What is the maximum volume of CSF that the ventricles and subarachnoid space can hold?

Answer 20

140ml

Question 21

Where does excess CSF drain?

Answer 21

Into the venous system via the arachnoid granulations.

Question 22

What is the function of CSF?

Answer 22

• Continous flow of CFS removes toxic metabolic by-products from the brain
• Protects brain from injury as it floats in CSF, reduces weight from 1.5kg to 50g

Question 23

How is a lumbar pucture perfomed and what information does it provide?

Answer 23

• Needle inserted between L3 and L4 as the spinal cord ends at L1/2
• Lumbar cistern: region with no spinal cord and enlarged subarachnoid space containing CSF
• Samples of CSF can be meaured for signs of infection, or to look for evidence of metabolic disturbances in the brain

Question 24

Which artery supplies the face and scalp?

Answer 24

External carotid artery.

Question 25

Which artery supplies blood to the base of the brain and which foramen does it enter the skull through?

Answer 25

Internal carotid artery, enters through formaen magnum.

Question 26

Which other arteries supply blood to the brain?

Answer 26

The vertebral arteries, arise from a branch of the subclavian artery and enters base of skull through foramen magnum.

Question 27

The vertebral arteries anastomose to form what single artery?

Answer 27

The basilar artery

Question 28

Describe the course of the basilar artery and what it divides into.

Answer 28

• Runs across the medulla and PONS until it reaches level of the midbrain
• Divides into the posterior cerebral arteries

Question 29

What does the posterior cerebral artery give rise to?

Answer 29

The posterior communicating artery

Question 30

What does the posterior communicating artery give rise to?

Answer 30

Connects with the internal carotid artery to give the anterior cerebral artery

Question 31

What is the blood network that supplies the base of the brain called?

Answer 31

The Circle of Willis

Question 32

What is the benefit of the circle of Willis stucture?

Answer 32

• Ensures that if there is a point of blockage to the blood supply at the base of the brain (internal carotis or vertebral), then you will still get adequate blood supply via the other artery.
  And if an artery in the circle is blocked, you can still have adequate blood supply by flowing blood the other way round the circuit.

Question 33

What other arteries does the basilar artery give rise to (other than the posterior cerebral arteries)?

Answer 33

• Pointine arteries which supply the Pons

- Cerebellar arteries which supply the cerebellum

Question 34

Describe the cortical blood supply.

Answer 34

• Middle cerebral artery supplies majority of the cerebral cortex, and most of the primary sensory and motor cortices
• Anterior cerebral artery supplies areas associated with legs and feet
• Posterior cerebral artery supplies primary visual areas

Question 35

Which sinus is found at the superior margin of the falx cerebri?

Answer 35

Superior sagittal sinus

Question 36

Which sinus is found at the inferior margin of the falx cerebri?

Answer 36

Inferior sagittal sinus

Question 37

Which sinuses are found at the margins of the tentorium cereblli?

Answer 37

• Straight, transverse and petrosal sinus

Question 38

Which sinuses do most other sinuses drain into?

Answer 38

Most drain into the transverse or sigmoid sinus, sigmoid sinus then drains directly into the internal jugular vein.

Question 39

Which sinus is found close to the sella turcica of the sphenoid bone, and where does it drain?

Answer 39

The cavernous sinus, drains into the facial vein (risk of infection).