Lecture 2: Cerebral Vasculature and Brain Homeostasis

Question 1

True or false?

Production of CSF is variable over a wide range of intracranial pressures.

Answer 1

FALSE!

Production of CSF is CONSTANT over a wide range of intracranial pressures.

Question 2

Blood vessels have their own sensory innervation. What NT will act on the blood vessels to dilate them? Why are the activated?

Answer 2

• Substance P
• Neurokini A
• CGRP

Activated if there is any torsion or manipulation and can lead to bad headaches

Question 3

What is the normal value of intracranial pressure necessary for CSF absorption?

Answer 3

112 mm CSF

Question 4

What does the Na⁺/K⁺/2 Cl^- transporter do?
What controls its expression?

Answer 4

• Transports ions from CSF to blood
• Controlled by release of endothelin 1 and 3 from endothelial cells of blood vessels
• Related to [K+] in CSF

Question 5

What areas of the brain lack the BBB?

Why?

Answer 5

Circumventricular Organs

1. Posterior Pituitary: needs to know what is going in blood to regulate hormones
2. Area Postrema: Detects toxins in blood and initiates vomiting in response to chemotactic triggers
3. Organum Vasculosum of Lamina Terminals (OVLT): regulation of total body water and thirst
4. Subfornical Organ: regulation of total body water and thirst

Question 6

Is CSF recirculated?

Answer 6

No

Blood is

Question 7

What is more acidic, CSF or plasma?

Answer 7

CSF

Question 8

What can increased intracranial pressure cause?

Answer 8

Damage to neurons

Question 9

What is BBB slightly permeable to?

Answer 9

• Na⁺
• Cl^-
• K⁺

Question 10

What uses the 45 K Glut 1 transporter?

Answer 10

Astroglia

Question 11

Where is CSF made?

Answer 11

• Main: Choroid Plexus
• Other: Tissue lining ventricles and blood vessels

Question 12

What connects the 3^rd ventricle to 4^th ventricle?

Answer 12

Cerebral Aquaduct

Question 13

What can cause torsion of blood vessels?

Answer 13

Reduced CSF causing brain to feel heavy

Basically decreased CSF –> brain moving more –> blood vessesl being torqued –> activate sensory neurons –> release of NT at torqued areas –> dilation of blood vessels

Question 14

How does plasma concentration compare to CSF?

Answer 14

• Same: Na⁺ and Bicarbonate
• CSF > Plasma: Cl^-, Mg²⁺, Carbon Dioxide
• CSF < Plasma: Protein, Glucose, K⁺, Ca²⁺

Question 15

Does the blood from ICA and Basilar Artery mix?

What does this mean if they do or do not?

Answer 15

No they do not

• Due to little mixing, there will be localized areas of ischemia in case of blood vessel damage

Question 16

What is the bare minimum of intracranial pressure necessary for CSF absorption?

Answer 16

68 mm CSF

Question 17

What happens if there is an increase of intracranial pressure?

Answer 17

Obstruction of venous outlflow and reduced cerebral blood flow

Question 18

What can cause an increase in intracranial pressure?

Answer 18

1. Hydrocephalus
2. Cerebral Edema
3. Infection
4. Intracranial Bleeding
5. Tumor Blockage

Question 19

What uses the 55 K Glut 1 transporter?

Answer 19

Capillaries

Question 20

What moves drugs that cross the BBB and don’t belong there?

Answer 20

P-glycoproteins

Question 21

What neurotrasmitters lead to sympathetic innervation of the cerebral circulation?

What do they do?

Answer 21

NT: Norepinephrine and Neuropeptide Y

• Receptors: alpha adrnergic
• Effects: blood vessel constriction and increase of bp

Question 22

In areas in the brain that are not enclosed by BBB, what do these capillaries lack?

Answer 22

Tight Junctions between endothelial cells

Question 23

What neurotrasmitters lead to parasympathetic innervation of the cerebral circulation?

What do they do?

Answer 23

NT: Acetylcholine, VIP, PHM-27

• Receptors: on large blood vessles
• Effects: vasodilation

Question 24

What is BBB highly permeable to?

Answer 24

• Water
• Carbon Dioxide
• Oxygen Lipid-soluble hormones (free)

Question 25

What are the functions of the BBB?

Answer 25

1. Protection from blood-borne agents 2. Maintains electrolyte composition of CSF and neural parenchyma 3. Excludes toxins 4. Contains neurotransmitters

Question 26

What is BBB not permeable to?

Answer 26

* Plasma * Proteins * Non-lipid soluble organic molecules

Question 27

Where can CSF be found?

Answer 27

* Ventricles (2 lateral, 3^rd, and 4^th) * Cisterns * Subarachnoid Space

Question 28

How does the body maintain constant cerebral blood flow when the mean arterial blood pressure is high?

Answer 28

Sympathetic stimulation will vasoconstrict vasculature and protect capillaries in the brain and BBB from damage

Question 29

What is the major energy source for neurons?

Answer 29

Glucose

Question 30

Absorption is ______ to intracranial pressure.

Answer 30

proportional

Question 31

Briefly, how is CSF made?

Answer 31

Filtration of plasma by choroid plexus

Question 32

What two components do capillaries have in the brain that composes the Blood Brain Barrier?

Answer 32

* Tight junctions between endothelial cells * Glial Endfeet (close contact with blood vessel)

Question 33

What connects the lateral ventricles to 3rd ventricle?

Answer 33

Foramen of Monro or Intraventricular Foramen

Question 34

What reabsorbs CSF? Where does CSF go next?

Answer 34

Arachnoid Villi * Fusion of endothelium of sinus and villi membane * Pinoctysosis plays role * _CSF will enter venous sinuses by bulk flow_

Question 35

What controls where cerebral blood flow will go?

Answer 35

Oxygen

Question 36

How does water enter the ventricles?

Answer 36

Net flux of Na⁺, Cl^-, and bicarbonate from the blood creates an _osmotic gradient_ that drives water into ventricles via _Aquaporin 1_

Question 37

When is cerebral blood flow low?

Answer 37

When mean arterial blood pressure is really low (\< 60 mm Hg)

Question 38

What is the function of CSF?

Answer 38

1. Cushioning 2. Distribution of secretory signals 3. Regulates neurogenesis 4. Waste clearance 5. Buoyancy for brain (significantly reduces weight of brain)

Question 39

What glucose transporter is utilized in the brain? What is special about this transporter?

Answer 39

**GLUT 1** (insulin independent) ## Footnote *Can be used all the time*

Question 40

When is cerebral blood flow constant?

Answer 40

When mean arterial blood pressure is between 60-140 mm Hg ## Footnote *Has to be really high before it is interrupted*

Question 41

How does fluid from the blood vessels move into the ventricles?

Answer 41

1. Fluid movement is dependent on hydrostatic and oncotic pressure. 2. The oncotic pressure of the choroid plexus cells and capillaries cancel each other out. 3. Due to the high hydrostatic pressure in the capillary, it pushes fluid out into the ventricles.