A02 The Ventricles, Cerebrospinal Fluid and Meninges

Question 1

List the layers of meninges surrounding the CNS.

Answer 1

1 - Dura mater.

2 - Arachnoid mater.

3 - Pia mater.

Question 2

What is the function of the meninges?

How does it do this?

Answer 2

• To anchor the CNS against sudden movement.

- This is facilitated by the presence of cerebrospinal fluid which forms a hydraulic cushion.

Question 3

List the layers that comprise the dura mater.

How does this change from the cranial region to the spinal region?

Answer 3

1 - Periosteal layer.

2 - Meningeal layer.

• Both layers are present in the cranial region, whereas only the meningeal layer is present in the spinal region.

Question 4

List the sheets of tissue formed by the meningeal layer of dura mater.

Answer 4

1 - Falx cerebri.

2 - Falx cerebelli.

3 - Tentorium cerebelli.

4 - Diaphragma sella.

Question 5

List the structures formed by the pia mater in the spinal cord.

Answer 5

1 - Denticulate ligament.

2 - Filum terminale.

Question 6

What is the subarachnoid space?

List 3 components of the subarachnoid space.

Answer 6

• A large space between the arachnoid mater and pia mater.

1 - Cerebrospinal fluid.

2 - Major vessels supplying the brain.

3 - Web-like trabeculations.

Question 7

What is the extradural space?

Answer 7

A potential space between the cranial bones (not the spine - the spine has the epidural space) and the endosteal layer of the dura mater.

Question 8

What is contained within the extradural space?

Answer 8

Branches of the middle meningeal artery.

Question 9

When might fluid form in the extradural space?

What is this condition known as?

Answer 9

• When trauma causes bleeding of the middle meningeal artery into the space.
• This condition is known as an extradural haematoma.

Question 10

What is the epidural space?

Answer 10

• In the spine, it is the space between the cranial bone and the dura mater.
• There is no epidural space in the brain.

Question 11

What is contained within the epidural space?

Answer 11

1 - Fat.

2 - Lymphatics.

3 - Blood vessels.

4 - Nerve roots.

Question 12

What is the subdural space / epiarachnoid space?

Answer 12

A potential place between the meningeal layer of dura mater and the arachnoid mater.

Question 13

List the contents of the forebrain / prosencephalon.

Answer 13

1 - Cerebrum / telencephalon.

2 - Diencephalon.

Question 14

List the contents of the midbrain / mesencephalon.

Answer 14

1 - Tectum.

2 - Cerebral aqueduct.

3 - Tegmentum.

4 - Cerebral peduncles.

Question 15

List the contents of the hindbrain / rhombencephalon.

Answer 15

1 - Cerebellum.

2 - Pons.

3 - Medulla oblongata.

Question 16

List the components of the brain stem from superior to inferior.

Answer 16

1 - Midbrain / mesencephalon.

2 - Pons.

3 - Medulla oblongata.

Question 17

List the ventricles of the ventricular system.

Answer 17

1 - 2 lateral ventricles.

2 - A third ventricle.

3 - A fourth ventricle.

Question 18

Where are the 2 lateral ventricles?

Answer 18

Deep to the lobes of the cortex.

Question 19

Where is the third ventricle?

Answer 19

In the midline between the thalami and the fourth ventricle.

Question 20

Where is the fourth ventricle?

Answer 20

Between the brainstem and cerebellum.

Question 21

What is the falx cerebri?

List its attachments.

Answer 21

• A crescent-shaped downward projection of the meningeal dura mater.
• It passes between the two cerebral hemispheres.
• It is attached anteriorly to the ethmoid and frontal bones.
• It is attached posteriorly to, and blends with, the tentorium cerebelli.

Question 22

What is the falx cerebelli?

List its attachments.

Answer 22

• A small midline projection of the meningeal dura mater.
• It is located in the posterior cranial fossa.
• Its anterior edge is free and lies between the two cerebral hemispheres.
• It is attached posteriorly to the occipital bone.
• It is attached superiorly to the tentorium cerebelli.

Question 23

What is the tentorium cerebelli?

List its attachments.

Answer 23

• A horizontal projection of the meningeal dura mater.
• It covers the cerebellum in the posterior cranial fossa from the posterior parts of the cerebral hemispheres.
• It is attached posteriorly to the occipital bone.
• It is attached laterally to the petrous part of the temporal bone.
• It ends anteriorly at the sphenoid bone. Its anterior and medial borders are free, forming an oval opening in the midline known as the tentorial notch.

Question 24

What is the diaphragma sellae?

List its attachments.

Answer 24

• A small horizontal projection of the meningeal dura mater.
• It covers the hypophyseal fossa in the sella turcica of the sphenoid bone.
• There is an opening in the center of the diaphragma sellae through which the infundibulum passes.

Question 25

What passes through the tentorial notch?

Answer 25

The brainstem at the junction of the midbrain and pons.

Question 26

Describe the gross structure of the components of venous drainage of the brain.

Answer 26

- Venous drainage begins internally as networks of small venous channels, which lead to larger veins that eventually empty into dural venous sinuses. - Also emptying into the dural venous sinuses are diploic veins, which run between the internal and external tables of compact bone in the roof of the cranial cavity, and emissary veins, which pass from outside the cranial cavity into the dural venous sinuses. - Dural venous sinuses are endothelial-lined spaces in the epidural space (between the periosteal and meningeal layers of the dura mater. - Dural venous sinuses empty into the internal jugular vein.

Question 27

List 4 dural venous sinuses. Make sure you can identify all of them on a diagram.

Answer 27

1 - Straight sinus. 2 - Superior and inferior sagittal sinuses. 3 - Left and right transverse sinuses. 4 - Paired cavernous sinuses.

Question 28

List the structures that are received by the paired cavernous sinuses. Make sure you can draw a coronal section of the paired cavernous sinuses.

Answer 28

1 - Cerebral veins. 2 - Ophthalmic veins. 3 - Emissary veins from the pterygoid plexus. 4 - Sphenoparietal sinuses. 5 - Oculomotor nerve (III). 6 - Trochlear nerve (IV) 7 - Ophthalmic nerve (V1). 8 - Maxillary nerve (V2). 9 - Abducens nerve (VI).

Question 29

What connects the right and left cavernous sinuses to form the paired cavernous sinuses?

Answer 29

The intercavernous sinuses on the anterior and posterior sides of the pituitary stalk.

Question 30

What are sphenoparietal sinuses?

Answer 30

- Dural venous sinuses that drain into the anterior ends of each cavernous sinus. - They run along the lesser wings of the sphenoid bone and receive blood from the diploic and meningeal veins.

Question 31

Describe the structure and location of the lateral ventricles.

Answer 31

- Each lateral ventricle follows a long C-shaped course through all of the lobes of the cerebral hemisphere. - They are divided into five parts. In order, they are: 1 - An anterior horn in the frontal lobe. 2 - A body in the frontal and parietal lobes. 3 - A posterior horn projecting posteriorly into the occipital lobe. 4 - An inferior horn curving inferiorly and anteriorly into the temporal lobe. 5 - An atrium / trigone where the body and posterior horn meet.

Question 32

List the ventricular cavities that exist in the forebrain, midbrain and hindbrain.

Answer 32

- The forebrain contains the lateral ventricles and the third ventricle. - The midbrain contains the cerebral aqueduct. - The hindbrain contains part of the fourth ventricle and part of the central canal.

Question 33

Through which structures do the lateral ventricles communicate with the third ventricle?

Answer 33

Interventricular foramina.

Question 34

Through which structure does the third ventricle communicate with the fourth ventricle?

Answer 34

The cerebral aqueduct.

Question 35

What lines the ventricles? What type of cell is this? What is the function of this lining?

Answer 35

- Ependymal cells. - Ciliated simple columnar epithelial cells (similar to mucosal epithelial cells). - To produce cerebrospinal fluid.

Question 36

What are the main structures that produce cerebrospinal fluid? Where are these structures located?

Answer 36

- The choroid plexuses. | - In the lateral, third and fourth ventricles.

Question 37

How much cerebrospinal fluid is produced per day?

Answer 37

0.6-0.7L per day.

Question 38

List 4 processes that propel cerebrospinal fluid.

Answer 38

1 - Pulsations of the choroid plexuses. 2 - Pulsations of arteries in the subarachnoid space. 3 - Motion of the cilia of ependymal cells. 4 - Normal movements of the brain and spinal cord during activity.

Question 39

What is the function of arachnoid trabeculae?

Answer 39

They aid in cushioning of the CNS.

Question 40

List the components of normal cerebrospinal fluid.

Answer 40

1 - Ions (Cl-, Mg2+, Na+, K+, Ca2+). 2 - Creatinine. 3 - Glucose. 4 - Albumin. 5 - Uric acid. 6 - Little protein. 7 - Little immune tissue.

Question 41

How would the appearance of cerebrospinal fluid change if a patient had meningitis? Why?

Answer 41

- The fluid changes from clear to cloudy. | - This is due to the increase in leukocytes in the fluid.

Question 42

Describe the circulation of cerebrospinal fluid.

Answer 42

- The cerebrospinal fluid produced by the choroid plexuses passes through the ventricular system to exit the fourth ventricle through the foramina of Luschka and Magendie. - The cerebrospinal fluid then enters the subarachnoid space, which it exits via two structures: 1 - By traversing the subarachnoid space to reach and enter arachnoid villi that extend into the superior sagittal sinus. From here, they enter the venous circulation via the lateral lacunae. 2 - By passing through small channels that extend from the subarachnoid space through openings in the cribriform plate of the ethmoid bone. The channels drain into nasal lymphatics and adjacent veins.

Question 43

What is a lumbar puncture? Briefly describe the procedure. List 3 contraindications for this procedure.

Answer 43

- The technique used to obtain a CSF sample and to indirectly measure intracranial pressure. - After administering a local anaesthetic, a needle is inserted between the spinous processes of L3 and L4 vertebrae into the subarachnoid space, form which the cerebrospinal fluid is taken. - Contraindications include: 1 - Raised intracranial pressure. 2 - Clotting factor deficiencies. 3 - Overlying skin infections.

Question 44

If the veins of the head and neck lack valves, what ensures venous return to the heart?

Answer 44

1 - Gravity. 2 - Pressure is sufficient in the venous system of the head and neck to ensure venous return.

Question 45

What is the most likely cause of blood in the cerebrospinal fluid?

Answer 45

A subarachnoid haemorrhage.