Protection of the Brain

Question 1

Describe how the brain is protected?

Answer 1

• by bone, meninges, and cerebrospinal fluid
• harmful substances are shielded from the brain by the blood-brain barrier

Question 2

Describe the Meninges

Answer 2

Three connective tissue membranes lie external to the CNS:

Dura mater, arachnoid mater, and pia mater

Question 3

What are the functions of the meninges?

Answer 3

• To **cover and protect **the CNS
• protect blood vessels and enclose venous sinuses
• contain cerebrospinal fluid (CSF)
• form partitions within the skull

Question 4

Describe the Dura Mater

Answer 4

• dura = tough
• Leathery, strong menninx composed of two fused fibrous connective tissue layers
• The two layers separate in certain areas and form dural venous sinuses
• Three dural septa extend inward and limit excessive movement of the brain

Question 5

Describe what the dural venous sinuses do

Answer 5

Sinuses collect the venous blood from the brain and direct itinto the internal jugular veins of the neck.

Sinus within the longitudinal fissure is the superior sagittal sinus

Question 6

What are the three dural septa that extend inward and limite movement of the brain?

Answer 6

Falx cerebri

Falx cerebelli

Tentorium cerebelli

Question 7

Where is the Falx cerebri located?

Answer 7

Falx cerebri is the fold that dips into the logitudinal fissure.

It’s anterior attachment point is the crista galli

Question 8

Where is the falx cerebelli located?

Answer 8

The falx cerebelli runs along the vermis of the cerebellum

Question 9

Where is the tentorium cerebelli located?

Answer 9

The tentorium cerebelli is horizontal dural fold extends into the transverse fissure

Question 10

What is Arachnoid Mater?

Answer 10

Arachnoid = resembling a spider [web]

The middle meninx, which forms a loose brain covering

Question 11

What separates Arachnoid Mater from Dura Mater?

Answer 11

Subdural space separates dura mater from the arachnoid mater

Question 12

What lies beneath the arachnoid space?

Answer 12

A wide subarachnoid space that contains CSF and large blood vessels

Question 13

What is the Arachnoid Villi?

Answer 13

The arachnoid villi protrude superiorly into the dural sinuses and permit CSF to be absorbed into venous blood

Question 14

What is Pia Mater?

Answer 14

pia = tender

Deepest meninx composed of delicate connective tissue that clings tightly to the brain at each sulcus and gyrus

Question 15

Describe Cerebrospinal Fluid (CSF)

Answer 15

• • watery solution similar in composition to blood plasma
• -contains less protein and different ion concentrations than plasma

Question 16

What are the functions of Cerebrospinal Fluid (CSF)?

Answer 16

• Forms a liquid cusion that gives buoyancy to the brain and spinal cord
• Prevents the brain from crushing under its own weight
• Protects the CNS from blows and other trauma
• Nourishes the brain and carries chemical signals throughout it

Question 17

Where is Cerebrospinal Fluid (CSF) located?

Answer 17

Contained within the ventricles & central spinal cord plus surrounds the brain and spinal cord (in subarachnoid space)

• Paird Lateral Ventricles (right and left)
• Third Ventricle
• Fourth Ventricle (between the pons and the cerebellum)
• Cerebral Aqueduct (canal which connects the third and Fourth Ventricles)

Question 18

What separates the paired Lateral Ventricles (left and right)?

Answer 18

The thin membrain called the septum pellucidum

Question 19

Where is the Third Ventricle located?

Answer 19

between the two halves of the thalamus

Question 20

How does the Third Ventricle communicate with the Lateral Ventricles?

Answer 20

via the interventricular foramen

Question 21

Where is Cerebrospinal Fluid (CSF) prodced?

Answer 21

CSF is produced by the Choroid Plexuses

Question 22

Describe the Choroid Plexuses

Answer 22

• clusters of capillaries which hang from the roof of each ventricle
• have ion pumps that allow them to alter ion concentrations of the CSF
• help cleanse CSF by removing wastes

Question 23

Clinical Correlates of protection of the brain:

What is Hydrocephalus?

Answer 23

Hydrocephalus is swelling in the ventricles and the sub-arachnoid space.

Question 24

Clinical correlates of Protection of the Brain

What causes hydrocephalus?

Answer 24

A mis-match in the rate of CSF production vs. removal

Question 25

Clinical correlates of Protection of the Brain

If not corrected, what will hydrocephalus lead to?

Answer 25

Intracranial pressure (ICP) which will ultimately damage brain tissue

Question 26

Clinical correlates of Protection of the Brain

How do you treat hydrocephalus?

Answer 26

Hydrocephalus requires a surgical shunt from the ventricle to another area of the body for reabsorption

Question 27

What is the Blood-Brain Barrier?

Answer 27

Protective mechanism that helps maintain a stable environment for the brain

Question 28

How are bloodborne substances separated from neurons in the Blood-Brain Barrier?

Answer 28

- continuous endothelium of capillary walls

• relatively thick basal lamina
• bulbuous feet of astrocytes

Question 29

What are the functions of the Blood-Brain Barrier?

Answer 29

• selective barrier that allows nutrients to pass freely
• protects against metabolic wastes, toxins, most drugs, nonessential amino acids and potassium ions
• ineffective against substances that con diffuse through plasma membranes

Question 30

What substances can diffuse through plasma membraines and make the Blood-Brain Barrier ineffective?

Answer 30

• Lipid soluble solutions and gases can diffuse through (basis of anesthesia)
• alcohol, caffeine and nicotine pass through easily
• absent in some areas (e.g., vomiting center of the hypothalamus), allowing these areas to monitor the chemical composition of the blood
• physical stress and certain disease states (e.g., high blood pressure) increase the ability of chemicals to pass through the BBB