Section 2

Question 1

What are the four principal protective measures for the CNS?

Answer 1

Bone, protective membranes, cerebrospinal fluid, and the blood-brain barrier

Question 2

T or F: The vertebrae of the spine provides a hard physical barrier as a protection against damage.

Answer 2

True

Question 3

List the layers of the head from outside to inside. (8)

Answer 3

Hair
Skull
Dura sinus
Dura mater
Arachnoid granulations
Arachnoid mater
Subarachnoid space
Pia mater

Question 4

What are the meninges?

Answer 4

The three membranes that wrap and contain the CNS.

They include (from outermost to innermost):
1. Dura mater
2. Arachnoid mater
3. Pia mater

Question 5

What is the dura mater?

Answer 5

• The outermost membrane
• Tough and double membrane
• Lies next to the bone (skull)
• For the most part, the two layers are always in direct contact but in certain regions they may be seperated to create blood-filled spaces called the dural sinuses (the larger ones are called venous sinuses). Venous blood draining from the brain empties into these sinuses to be returned to the heart. Cerebral spinal fluid can also drain into them.

Question 6

What is the arachnoid mater?

Answer 6

• The middle meninges
• More delicate and highly vascularized
• In the area of the dural sinuses, projections of the arachnoid mater called arachnoid granulation villi penetrate through the dura and expand into the sinuses. This allows transfer of CSF from the subarachnoid space (space between arachnoid mater and pia mater) to cross the villi to the blood of the sinuses

Question 7

What is pia mater?

Answer 7

• the innermost membrane
• highly vascularized
• tightly adheres to the surface of the brain and the spinal cord
• in certain areas, it digs deeper into the brain to bring blood supply to the ependymal cells lining the ventricles

Question 8

What is the cerebrospinal fluid? Where is it found, and what are its functions?

Answer 8

• it protects the brain as a shock-absorber
• the density of the CSF is similar to the brain tissue which allows the brain to be suspended in it
• it is located in the subarachnoid space (between the arachnoid mater and the pia mater)
• it is essential for the transfer of materials between the blood and neural tissues. The brain’s interstitial fluid surrounds and supplies the neurons and glial cells. While neither the CSF nor the blood stream are in direct contact with the interstitial fluid, they do influence its composition. The CSF has a stronger influence than the blood stream, and therefore is highly regulated.

Question 9

What is the role of the CSF in protecting the brain?

Answer 9

CSF serves as a shock-absorber, providing protection to the brain.

Question 10

How does CSF help suspend the brain in a buoyant manner?

Answer 10

The density of CSF is similar to that of brain tissue, allowing the brain to be suspended in it.

Question 11

Where is CSF located within the brain and spinal cord?

Answer 11

CSF is located in the subarachnoid space, which is between the arachnoid mater and the pia mater.

Question 12

What is the essential function of CSF regarding material transfer and brain health?

Answer 12

CSF is crucial for the transfer of materials between the blood and neural tissues. It surrounds and supplies neurons and glial cells with nutrients and regulates their environment. CSF has a stronger influence on brain interstitial fluid composition compared to the bloodstream, making it highly regulated.

Question 13

True or false: Choroid plexuses create CSF?

Answer 13

True.

Question 14

What are choroid plexuses, and where are they located?

Answer 14

They are highly vascularized masses of pia mater that extend into pockets of ependymal cells to produce CSF.

Each of the four ventricles contains a choroid plexus.

Question 15

How much CSF is in the brain, and how often is it replaced?

Answer 15

The total volume of the CSF is approximately 125 to 150 mL, and this volume gets replaced more than three times a day.

Question 16

Where are choroid plexuses found in the brain?
a) In the cortex
b) In the white matter
c) In the ventricles
d) In the spinal cord

Answer 16

c) In the ventricles.

Question 17

How often is the entire volume of cerebrospinal fluid (CSF) replaced in the brain?
a) Once a week
b) Once a day
c) More than three times a day
d) Never

Answer 17

c) More than three times a day.

Question 18

What is the initial path of CSF after production?
a) Through the spinal cord
b) Through the blood vessels
c) Through the ventricles
d) Through the bones

Answer 18

c) Through the ventricles. CSF flows through the ventricles in the brain.

Question 19

Where can CSF enter from the fourth ventricle?
a) Arachnoid villi
b) Subarachnoid space
c) Central canal of the spinal cord
d) Bloodstream

Answer 19

b) Subarachnoid space. CSF can enter the subarachnoid space within the fourth ventricle.

Question 20

What path does CSF follow in the subarachnoid space?
a) It doesn’t flow in the subarachnoid space.
b) It flows through blood vessels.
c) It flows between meningeal layers.
d) It flows through the bones.

Answer 20

c) It flows between meningeal layers in the subarachnoid space.

Question 21

Besides the brain, where else does CSF flow?
a) Muscles
b) Lungs
c) Central canal of the spinal cord
d) Skin

Answer 21

c) Central canal of the spinal cord.

Question 22

How is CSF reabsorbed from the subarachnoid space?
a) Through blood vessels
b) Through the spinal cord
c) Through arachnoid villi
d) Through the bones

Answer 22

c) Through arachnoid villi. CSF is reabsorbed from the subarachnoid space through the arachnoid villi.

Question 23

Where does CSF go after being reabsorbed?
a) Back to the choroid plexuses
b) Into the lungs
c) Into the venous blood
d) Into the muscles

Answer 23

c) Into the venous blood. CSF enters the venous blood circulation after reabsorption.

Question 24

The blood brain barrier. Unlike the rest of the body where there is exchange of nutrients and other materials between the capillaries and the interstitial spaces, this does not occur in the brain. The endothelial cells of brain capillaries are joined together by tight junctions to prevent materials from passing between the cells. Because of this, the exchange of materials between the blood and the brain must pass through the endothelial cells and is therefore highly regulated. This is very important in that sudden changes in blood plasma composition will not influence the composition of the brain’s interstitial fluid and affect neuronal function.

Question 25

True or False: In the brain, there is an exchange of nutrients and materials between capillaries and interstitial spaces.

Answer 25

False. Unlike the rest of the body, in the brain, there is no exchange of nutrients and materials between capillaries and interstitial spaces.

Question 26

What prevents materials from passing between endothelial cells in brain capillaries?
a) Tight junctions
b) Loose junctions
c) Gap junctions
d) Adherens junctions

Answer 26

a) Tight junctions. Tight junctions between endothelial cells in brain capillaries prevent materials from passing between them.

Question 27

Why is the exchange of materials between blood and the brain highly regulated?
a) To make it faster
b) To prevent exchange
c) To promote brain health
d) To decrease neuronal function

Answer 27

b) To prevent exchange. The exchange of materials between blood and the brain is highly regulated to prevent sudden changes in blood plasma composition from affecting the brain’s interstitial fluid and neuronal function.

Question 28

Why is the blood-brain barrier important?
a) To allow free flow of materials
b) To maintain a consistent brain environment
c) To speed up neuronal function
d) To allow rapid changes in blood composition

Answer 28

b) To maintain a consistent brain environment. The blood-brain barrier is crucial for ensuring that sudden changes in blood plasma composition do not influence the brain’s interstitial fluid and impact neuronal function.