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Neuro Exam 2 - JLJ > Cerebral Vasculature and CNS Homeostasis > Flashcards

Cerebral Vasculature and CNS Homeostasis Flashcards

1
Q

How much CSF do we have at any given moment? How much CSF do we make per day?

A

150 mL at any moment; 550 mL made per day

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2
Q

What ventricles are connected through the intraventricular foramen?

A

Lateral ventricles to the 3rd ventricle

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3
Q

What ventricles are connected through the cerebral aqueduct?

A

3rd ventricle to the 4th ventricle

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4
Q

What is connected through the median aperture?

A

4th ventricle to the cisterna magna

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5
Q

What is connected through the lateral apertures?

A

4th ventricle to the arachnoid space

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6
Q

What makes most of the CSF? What is the percentage?

A

Choroid plexus makes 50-70% of the CSF; the rest is made by tissue that lines the ventricles and blood vessels

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7
Q

What is step 1 of the formation of CSF?

A

Passive filtration of serum, dependent on hydrostatic pressure and oncotic/osmotic pressure

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8
Q

What is hydrostatic pressure in the capillary?

A

Equivalent to blood pressure; pushes fluid out; usually large

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9
Q

What is hydrostatic pressure surrounding the capillary?

A

Also called tissue hydrostatic pressure; pushes fluid into capillary; usually small

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10
Q

What is osmotic pressure in the capillary?

A

Pulls fluid into the capillary

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11
Q

What is osmotic pressure surrounding the capillary?

A

Pulls fluid out of the capillary

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12
Q

Describe osmotic pressure at the choroid plexus

A

Equal and opposite; the 2 osmotic pressures cancel each other out

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13
Q

Describe hydrostatic pressure at the choroid plexus

A

Blood pressure in the capillary > tissue hydrostatic pressure

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14
Q

What is the net flow of fluid at the choroid plexus?

A

Fluid moves from the blood vessels into the ventricles

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15
Q

What is step 2 of the formation of CSF?

A

Modification of ion composition; HCO3, Cl, and K concentrations are controlled by channels on epithelial cells; aquaporin 1 allows H2O to cross

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16
Q

T/F: Production of CSF is constant over a very narrow range of intracranial pressures

A

False; production of CSF is constant over a wide range of intracranial pressures

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17
Q

What ions tend to end up in equal concentrations in both plasma and the CSF?

A

Na and HCO3

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18
Q

What ions tend to be greater in the CSF than the plasma?

A

Mg, Cl, CO2

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19
Q

What ions tend to be less in the CSF than the plasma?

A

K, Ca, protein, glucose

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20
Q

What is the arachnoid villi? What is its function?

A

Endothelium of sinus and the membrane on the villi have fused; functions in reabsorbing CSF after it has flowed through the ventricular system

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21
Q

Absorption of CSF at arachnoid villi is proportional to intracranial pressure. At pressures below 68 mm CSF, what happens? At normal pressure (around 112 mm CSF), what happens? What does increased pressure cause?

A

Below 68 mm CSF: no absorption

Normal: absorption

Increased Pressure: causes damage to neurons

22
Q

After being reabsorbed by the arachnoid villi, what happens to the CSF?

A

CSF enters venous sinuses via “bulk flow”

23
Q

What limits exchange in the capillaries of the brain?

A

Tight junctions between endothelial cells and glial endfeet that come in close contact with a blood vessel

24
Q

What are some substances that can cross the BBB?

A

H2O (via aquaporin 4), CO2, O2, free steroid hormones (most are protein bound)

25
Q

What is the major energy source of neurons? How does this cross the BBB?

A

Glucose, which does NOT cross the BBB readily; crosses BBB via GLUT 1

26
Q

What are the 2 forms of GLUT 1 that help glucose cross the BBB and where are they found?

A

55k: found on capillaries
45k: found on astroglia

27
Q

What do neurons actually use to bring glucose in?

A

GLUT 3

28
Q

What controls the expression of the Na/K/2Cl transporter? What is its expression related to?

A

Controlled by release of endothelin 1 and 3 from endothelial cells of the blood vessels; seems to be related to [K] in CSF

29
Q

What is p-glycoprotein?

A

Pump glycoprotein; binds to a wide variety of substances

Many drugs do cross BBB but are moved back to the blood via p-glycoprotein

30
Q

What is the function of the BBB?

A

Protect the chemical composition of the CSF from blood-borne pathogens; maintains electrolyte composition, particularly K; also functions in maintenance of Vm and offers protection from toxins

31
Q

Describe how the BBB is “handicapped” in some portions of the brain

A

There are 4 regions of the brain that require exposure to blood-borne substances to function; in these regions, the capillaries do NOT have the tight junctions between endothelial cells

32
Q

What are circumventricular organs?

A

Neural tissue that is “outside” or not as well protected by the BBB as other neural tissue

33
Q

What are the 4 circumventricular organs?

A

Posterior pituitary, area postrema, organum vasculosum of the lamina terminalis (OVLT), and subfornical organ

34
Q

What is the function of the posterior pituitary?

A

Releases hormones into blood

35
Q

What is the function of the area postrema?

A

Controls vomiting

36
Q

What is the function of the organum vasculosum of the lamina terminalis (OVLT) and the subfornical organ?

A

Involved in control of body water/thirst/blood volume control

37
Q

How much blood is required in cerebral circulation per minute?

A

750 mL/min (14% of blood pumped from heart every minute)

38
Q

What forms the Circle of Willis?

A

2 internal carotid arteries and the basilar artery

39
Q

What happens if you disrupt one of the inputs to the Circle of Willis?

A

Localized ischemia; despite appearance, there is little mixing of the blood from the different sources

40
Q

For sympathetic innervation of cerebral circulation, what neurotransmitters are involved? What receptors are involved? What is the function of this sympathetic innervation?

A

Neurotransmitters: norepinephrine and neuropeptide Y (NPY)

Receptors: alpha-adrenergics

Function: leads to constriction when systemic cardiac output/blood pressure increases

41
Q

For parasympathetic innervation of cerebral circulation, what neurotransmitters are involved? What receptors are involved? What is the function of this parasympathetic innervation?

A

Neurotransmitters: acetylcholine, vasoactive intestinal polypeptide (VIP), and PHM-27 (derived from pre-pro-VIP)

Receptors:

Function: innervates larger blood vessels and causes vasodilation

42
Q

T/F: There is sensory innervation of the distal blood vessels

A

True

43
Q

What neurotransmitters are involved in sensory innervation of the distal blood vessels and what is their function?

A

Substance P (dilation), neurokinin A (dilation), and CGRP (dilation)

44
Q

What are sensory fibers to the blood vessels sensitive to?

A

Torsion/manipulation that can lead to pain; excruciating headaches

45
Q

What is the function of these sensory fibers to the blood vessels?

A

In the presence of low CSF, the brain is “heavier” and simple motion can cause pain because of “torsion” on the vessels; activation of these afferents will cause vasodilation and increase blood flow, returning total intracranial volume closer to normal

46
Q

What dictates where in the brain blood will go?

A

Oxygen consumption

We use these changes in brain metabolism/blood flow to infer activity in a variety of circumstances

47
Q

T/F: Cerebral blood flow is strongly autoregulated - it is held constant over a wide range of systemic (mean arterial) blood pressures

A

True

48
Q

In the face of high blood pressure (which could damage the BBB), sympathetics in the brain will __________ the vasculature.

A

Vasoconstrict

Note that although this will increase the systemic vascular resistance, it protects the capillaries in the brain and the BBB from damage

49
Q

What happens when intracranial pressure goes up?

A

Venous outflow is obstructed, leading to reduced arterial flow; this decrease in brain perfusion will activate cardiovascular control centers in the medulla and increase systemic BP

50
Q

What might increase the intracranial pressure?

A

Hydrocephalus of any variety, cerebral edema, and intracranial bleeding

Neuro Exam 2 - JLJ (16 decks)

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