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NE Exam 2 > CNS Homeostasis > Flashcards

CNS Homeostasis Flashcards

1
Q

How much blood is required by the brain per minute?

A

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

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2
Q

What happens if there is disruption of one of the inputs of Circle of Willis?

A

Localized (discrete) areas of ischemia rather than global effects – due to fact that there is little mixing of the blood from different sources in the circle of willis

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3
Q

Internal Carotid As

A
  • Anterior circulation
  • MCA & ACA
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4
Q

Basilar A

A
  • Posterior circulation
  • Blood from this A does not mix with ICAs
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5
Q

Systemic Circulation: Sympathetic Chemical Mediators

A
  • Epinephrine (Adrenal Gland via blood)
  • Norepinephrine (from nerve endings)
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6
Q

Systemic Circulation: Sympathetic Receptors

A
  • Alpha-adrenergic (contraction, vasoconstriction)
  • Beta-adrenergic (relaxation, vasodilation)
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7
Q

Systemic Circulation: Sympathetic Significance

A

Critical to maintain BP

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8
Q

Systemic Circulation: PNS Chemical Mediators

A

ACh

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9
Q

Systemic Circulation: PNS Receptors

A

Muscarinic (relaxation, vasodilation)

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10
Q

Systemic Circulation: PNS Significance

A
  • Minor direct influence
  • More likely to influence via indirect mechanisms
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11
Q

Cerebral Circulation: Sympathetic Chemical Mediators

A
  • Norepinephrine
  • Neuropeptide Y (NPY)
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12
Q

Cerebral Circulation: Sympathetic Receptors

A

Alpha-adrenergic (contraction, vasoconstriction)

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13
Q

Cerebral Circulation: Sympathetic Significance

A
  • Protection of cerebral capillaries
  • Critical when systemic BP is high
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14
Q

Cerebral Circulation: Sympathetic Innervation

A

Leads to vasoconstriction when systemic CO/BP increases

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15
Q

Cerebral Circulation: PNS

A

Innervation of larger blood vessels in brain

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16
Q

Cerebral Circulation: PNS Chemical Mediators

A
  • ACh
  • Vasoactive Intestinal Polypeptide (VIP)
  • PHM-27 (derived from pre-pro-VIP)
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17
Q

Cerebral Circulation: PNS Receptors

A

Muscarinic (ACh)

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18
Q

Cerebral Circulation: PNS Significance

A

Unknown

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19
Q

Cerebral Circulation: Parasympathetic Innervation

A

Causes vasodilation

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20
Q

There is ___ innervation of the distal blood vessels

A

Sensory
(means there are nociceptors)

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21
Q

3 main NTs that are released and act on cerebral blood vessels:

A

(1) Substance P
(2) Neurokinin A
(3) CGRP (Calcitonin-gene related peptide)

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22
Q

Substance P

A

Associated with pain

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23
Q

Neurokinin A

A

Associated with damage

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24
Q

CGRP

A

Associated with migraines

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25
Q

Sensory fibers within cerebral circulation are extremely sensitive to ___ /____ and lead to ___

A
  • Torsion/manipulation
  • Pain
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26
Q

Cerebral sensory innervation and reduction of CSF volume

A

Brain is heavier and simple motion can cause pain because of the torsion of the blood vessels

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27
Q

Activation of sensory afferents in cerebral circulation causes ____ and increased ___ ___

A
  • Vasodilation
  • Blood flow

(Brain does this b/c it is trying to bring intracranial volume back to normal until can make more/new CSF)

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28
Q

Systemic Circulation: innervated by sensory fibers?

A

Yes

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29
Q

Systemic Circulation: sensory fibers vasoactive?

A

Yes - Nociceptors

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30
Q

Systemic Circulation: Sensory Innervation Chemical Mediators

A

Substance P

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31
Q

Cerebral Circulation: innervated by sensory fibers?

A

Yes

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32
Q

Cerebral Circulation: sensory fibers vasoactive?

A

Nociceptors - Yes

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33
Q

Cerebral Circulation: Sensory Innervation Chemical Mediators

A
  • Substance P
  • NKA
  • CGRP
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34
Q

Cerebral Circulation: Sensory Innervation Receptors

A

Nociceptors

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35
Q

Cerebral Circulation: Sensory Innervation Effects

A

Sensation of pain when head moves

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36
Q

Cerebral Circulation: Sensory Innervation Significance

A
  • Tied with migraines
  • BP significant when have low CSF levels
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37
Q

Cerebral blood flow is under ___ control

A

Local

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38
Q

What dictates where in the brain the blood will go?

A

Oxygen consumption

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39
Q

Cerebral blood flow is strongly ______

A

Autoregulated
- it is held constant over a wide range of systemic (mean arterial) BPs

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40
Q

Location of the synapse between pre-ganglionic and post-ganglionic neurons of the sympathetic nervous system

A

Paravertebral ganglia (sympathetic chain)

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41
Q

Alpha-Adrenergic Receptors

A
  • Located on smooth muscle
  • Activated by SNS (when systemic BP increases beyond normal limits)
  • When activated, cause increased smooth muscle contraction, vasoconstriction and reduced blood flow to the organs receiving blood from the constricted arteries
  • Primary adrenergic receptor found on the cerebral vasculature
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42
Q

Nicotinic Receptors

A
  • Located in the synapses between pre-ganglionic and post-ganglionic neurons of both the sympathetic and parasympathetic systems
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43
Q

___ pressure in the brain is maintained constant over a wide range of systemic MAPs

A

Perfusion

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44
Q

As systemic BP increases:

A
  1. Sympathetic innervation of the cerebral vasculature becomes more active
  2. Release more NE
  3. Binds to alpha-adrenergic receptors
  4. Vasoconstriction of cerebral vasculature

Effect: protects the blood brain barrier

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45
Q

With high perfusion pressure, the ___ ___ between endothelial cells of the capillaries are damaged

A

Tight Junctions

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46
Q

Vasoconstriction of the arterioles during high BP prevents:

A

Pressure from being transmitted to the capillaries, which in turn preserves the BBB and the brain

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47
Q

Systolic BP of ___ mmHg will damage the BBB temporarily

A

180

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48
Q

If perfusion pressure of the brain is decreased (due to increased intracranial pressure):

A
  • Brain acts to increase BP via centers in the brainstem that detect and control BP
  • Reduced blood flow triggers increase in systemic MAP even if systemic BP is normal/high
  • Brain acting to preserve its own blood flow
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49
Q

What can happen if blood flow to the brain is severely compromised?

A

Systemic BP can go incredibly high

50
Q

Sign of an increase in intracranial pressure (i.e intracranial hemorrhage):

A

Increase in systemic BP

51
Q

Sensory innervation of the brain via nociceptors are activated by torsion (twisting, stretching) of the blood vessels and produce:

A

Intense Headache

52
Q

Why is a headache common after a lumbar puncture?

A

Decreased CSF volume means the brain is “heavier” and can now torque with normal motion –> pressure on distal blood vessels –> activation of nociceptors on distal blood vessels in the brain –> pain/headache

53
Q

What is the one substance that is present in higher concentrations in the CSF than the plasma?

A

Magnesium

54
Q

When below BP MAP of 60 mmHg, as MABP increases Cerebral Blood Flow (CBF) will:

A

Increase

55
Q

Cerebral Blood Flow held constant between what MABPs?

A

60 mmHg to 140 mmHg

56
Q

___ extends the range at which MABP is held constant – protects capillaries and blood-brain barrier from damage

A

Sympathetics

57
Q

As BP increases, sympathetics in brain trigger release of ___ and binding to its receptors

A

NE
(results in vasoconstriction)

58
Q

Cerebral blood flow is influenced by ___ ___

A

Intracranial Pressure

59
Q

As intracranial pressure goes up, __ ___ is obstructed, leading to ____ arterial flow

A
  • Venous outflow
  • Reduced
60
Q

Decrease in brain perfusion will activate the cardiovascular control centers in the __ and increase ___ ____

A
  • Medulla
  • Systemic BP (increases blood flow by increasing heart rate and BP)
61
Q

3 things that can increase ICP:

A
  • Hydrocephalus
  • Cerebral edema
  • Intracranial bleeding
62
Q

Activation of the sympathetics ___ resistance and is used when systemic BP is ___

A
  • increases
  • HIGH
63
Q

What happens when there is cerebral edema?

A

Decreased perfusion to the brain –> increased blood flow –> increased HR and BP

*brain doesn’t care that systemic BP rises b/c only cares about brain

64
Q

How much CSF do you have at any given moment?

A

150 mL

65
Q

CSF not recirculated, so make about ____ ml /day of CSF

A

550

66
Q

Intraventricular Foramen

A

Connects the Lateral Ventricles to the 3rd Ventricle

67
Q

Cerebral Aqueduct

A

Connects the 3rd Ventricle to the 4th Ventricle

68
Q

Median Aperture (Foramen of Magendie)

A

Connects the 4th Ventricle to the Cisterna Magna

69
Q

Lateral Aperture (Foramen of Luschka)

A

Connects 4th Ventricle to the Subarachnoid Space

70
Q

Where is CSF produced?

A
  • Choroid Plexus (50-90%)
  • Remaining CSF made by the tissue that lines the ventricles and blood vessels
71
Q

Two-Step Process of CSF formation by the Choroid Plexus

A
  • Step 1: Creation of Osmotic Gradient
  • Step 2: Movement of water across membrane
72
Q

CSF Formation in Choroid Plexus: Step 1, Creation of Osmotic Gradient

A

Relies on existence of transport proteins on the membrane, many of which are ATP dependent or co-dependent

73
Q

Ions that are critical in creating the Osmotic Gradient for CSF Formation:

A
  • Na
  • K
  • Cl
  • HCO3
74
Q

CSF Formation in Choroid Plexus: Step 2, Movement of Water Across the Membrane

A

Aquaporin-1 allows H2O to cross and follow the osmotic gradient

75
Q

Production of CSF is constant over a wide range of ___ ____

A

Intracranial Pressures
(having CSF is so critical that will not stop producing it no matter what)

76
Q

The further away CSF gets from Choroid Plexus, the more ___ it gets from the concentration of plasma

A

Different

77
Q

Components that have higher concentrations in CSF than they do in Plasma ([X]CSF > [X]Plasma):

A
  • Na
  • Mg
  • Cl
78
Q

Components that have lower concentrations in CSF than they do in Plasma ([X]CSF < [X]Plasma):

A
  • K
  • Ca
  • Protein
  • Glucose
79
Q

What component is in equal concentrations in both the plasma and CSF?

A

HCO3-
(maintains acid/base composition)

80
Q

Why is it important that [K+] is lower in CSF than plasma?

A
  • AP repolarization occurs when K+ leaves the cell
  • Need this so APs can occur
81
Q

CSF is absorbed by:

A

Arachnoid granulations/villi

82
Q

Absorption of CSF is ___ to ICP

A

Proportional

*make CSF continuously but control how much is reabsorbed

83
Q

Absoprtion of CSF when CSF pressure is below 68 mm:

A

No absorption

84
Q

What is normal pressure of CSF?

A

112mm

85
Q

From the arachnoid granulations, CSF enters the venous sinuses by ___ flow

A

Bulk

86
Q

Role of CSF:

A

protect the brain

87
Q

Capillaries in the brain have two components that limit exchange:

A
  • Tight junctions between endothelial cells
  • Glial end feet come in close contact with blood vessel
88
Q

Glian endfeet in contact with blood vessels are nearly:

A

continuous, creating perivascular space

89
Q

Substances that can cross BBB via passive diffusion

A
  • H2O
  • CO2
  • O2
  • Free steroid hormones (most are protein bound)
90
Q

How can H2O cross the BBB?

A

Via Aquaporin-4

91
Q

What is the major energy source for neurons?

A

Glucose - does not readily cross the BBB

92
Q

How does Glucose get across the BBB?

A

GLUT 1 transporter

93
Q

Is GLUT1 insulin-dependent?

A

No

94
Q

Two forms of GLUT1 receptors:

A
  1. 55K
  2. 45K
95
Q

Where are 55K GLUT1 receptors located?

A

Capillaries (endothelial cells)

96
Q

Where are 45K GLUT1 receptors located?

A

Astroglia

97
Q

What do neurons use to move glucose in?

A

GLUT3

98
Q

Na/K/2 Cl Transporter

A

Moves ions from CSF into blood

99
Q

What controls the expression of the Na/K/Cl transporter in the BBB?

A

Release of endothelin 1 and 3 from endothelial cells of the blood vessels

100
Q

The expression of the Na/K/2Cl transporter seems to be related to:

A

The control of [K+] in the CSF

101
Q

P-Glycoprotein

A
  • Pump Glycoprotein
  • Binds a wide variety of substances in the CSF (i.e drugs) and moves them back into the blood
102
Q

Gene that codes for P-Glycoprotein:

A

MDR1 (multi-drug resistance protein 1)

103
Q

BBB Function

A
  • Protects the chemical composition of the CSF form blood-borne agents
  • Maintains electrolyte composition — particularly related to K+, maintenance of Vm
  • Protection from toxins
104
Q

Glymphatics

A

Glial-dependent waste clearance pathway in the brain

105
Q

Glymphatics: Step 1

A

Water leaves the periarterial space via Aquaporin 4 (AQP4)

106
Q

Glymphatics: Step 2

A

Water exiting creates flow of ISF/CSF through the parenchyma of the brain; anything dissolved in the ECF/ISF moves with it

107
Q

Glymphatics: Step 3

A

Fluid moves into perivascular spaces around the venules/veins; this is also dependent on AQP4

(creates continuous flushing of fluid around the neurons)

108
Q

What two proteins expressed by Astroglia are instrumental in moving beta-amyloid into the perivenous space and out of the brain?

A
  • APOE
  • APOJ
109
Q

Glymphatics: Step 4

A

Fluid enters the cervical lymphatics

110
Q

When does Glymphatic flow occur?

A

During sleep

111
Q

There is evidence of active suppression of glymphatic flow by ___ receptors when we are awake

A

Adrenergic

112
Q

Glymphatic flow is decreased by:

A
  • Age
  • Brain ischemia or TBI
113
Q

What is the main cause of decreased glymphatic flow?

A

Abnormal cellular localization of AQP4 (typically located at the end feet but in this case they are found in other parts of the astroglia’s membrane)

114
Q

Circumventricular Organs

A
  • Neural tissue that is “outside” or not as well protected by the BBB as other neural tissue
  • Regions where the capillaries do not have tight junctions between endothelial cells
  • Can be secretory (no BBB so can secrete hormones) or sensory (no BBB so they can sense blood composition)
115
Q

4 Main Circumventricular Regions

A

(1) Posterior Pituitary
(2) Area Postrema
(3) Organum Vasculosum of Lamina Terminalis (OVLT)
(4) Subfornical Organ

116
Q

Circumventricular Regions: Posterior Pituitary

A
  • Also called the Neurohypophysis
  • Modified neural tissue
  • Release peptide hormones into blood
  • Secretory
117
Q

Circumventricular Regions: Area Postrema

A
  • Area that elicits vomiting because it is chemosensitive
  • Sensory – detects chemicals then elicits vomiting
118
Q

Circumventricular Regions: OVLT and Subfornical Organ

A
  • Both are involved in control of body water/thirst/blood volume control
  • Sensory
119
Q

Circumventricular Regions: Purpose

A

Allow parts of brain access to plasma composition

120
Q

Circumventricular Regions: Consequences

A

Exposed to toxins that rest of brain is protected from

121
Q

Location of Cell Bodies of Post-Ganglionic Sympathetic Fibers That Innervate Cerebral Vasculature?

A

Superior Cervical Ganglion

NE Exam 2 (19 decks)

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