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HSC 350 > Lecture 2, 3 > Flashcards

Lecture 2, 3 Flashcards

1
Q

What is cerebral blood flow and how is it maintained?

A

Cerebral blood flow (CBF)= 750-1000mL/min
Optimal CBF maintained by autoregulation, where arterioles constrict when systemic blood pressure is raised and dilate when it is lowered
Regional CBF must meet the demands of rapidly changing O2 and glucose metabolism and byproducts (which ever areas of brain are being used more, want more blood/O2 to go there- functional hyperemia)

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2
Q

What is an fMRI and it’s use with brain?

A

Functional magnetic resonance imaging
Blood flow follows changes in brain cellular activity

Look at slide 2 lecture 2

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3
Q

What is the BOLD effect?

A

Blood Oxygen Level Dependant
Increased blood flow to activated brain regions supplies more oxygenated blood than is immediately necessary for local metabolism

The bold signal reflects changes in the ratio of oxyhemoglobin to deoxyhemoglobin (who’s values vary with perfusion and metabolism)
Docyhemoglobin is paramagnetic (attracted to magnetic field, oxyhemoglobin is not

Slide 3 lecture 2

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4
Q

What are the 3 steps of magnetic resonance imaging?

A
  1. Protons align in the direction of a magnetic field (vertical). A horizontal radio frequency pulse is applied and tips the protons so they rotate in the horizontal plane “in phase” with eachother
  2. Horizontal pulse is turned off rotating protons begin to dephase
  3. Protons are realigned with vertical magnetic field only

Slides 4-6 lecture 2

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5
Q

What are cerebral ventricles?

A

Cerebral ventricles are a series of interconnected spaces filled with cerebrospinal fluid (CSF) that kid in the core of the forebrain and brainstem

Slide 7 lecture 2

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6
Q

What is the cerebrospinal fluid?

A

Clear, colourless fluid in ventricles and subarachnoid space around the brain and spinal cord
99% water, proteins, glucose, Na, K, H/HCO3, Ca, etc
No rbc and very little wbc

Functions to cushion and protect CNS from trauma, provides mechanical buoyancy and support for brain, serves as lymphatic system for brain (important for maintaining constant external environment for neurons and glia

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7
Q

What is the homeostasis of interstitial fluid in brain and cerebrospinal fluid in intraventricular and subarachnoid spaces regulated by?

A

Homeostasis of these fluid compartments is regulated to a great degree by the blood-brain and blood-CSF barriers

Slide 11-12 lecture 2

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8
Q

How does oxygen availability change for resting and active state?

A

Resting- we can see that within the vessel there is an equal amount of oxygenated vs deoxygenated blood

Active- in the active state there is much more oxygenated hemoglobin
There is a change in the ratio as to how much hemoglobin is oxygenated vs how much is deoxygenated

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9
Q

Why must astrocytes take up potassium?

A

Potassium must be taken up by the astrocytes to keep everyone (the neurons) happy and avoid activation when unnecessary
Hyper activation of the neuron causes neurotic damage

Slide 14 lecture 3

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10
Q

How is the cerebrospinal fluid formed?

Where, choroid plexus?

A

Formed in the lateral, third, and fourth ventricles by the choroid plexuses

Choroid plexus is a network of vessels derived from the pia covered with cuboidal epithelium of the ependyma

Slides 15-16 lecture 3

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11
Q

How is the cerebrospinal fluid secreted?

By what and how

A

CSF secretion by the choroid plexus

  1. Vascular epithelial cells are fenestrated
  2. Cuboidal epithelium set up an osmotic gradient created by the active transport of solutes

CSF is entirely recirculated 2/3 times a day

Slide 17-18 lecture 3

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12
Q

What are the 2 sequential stages the cerebrospinal fluid forms in?

A
  1. Ultrafiltration of plasma occurs across the fenestrated capillary wall into the ECF (epithelial cell filtrate) beneath the basolateral membrane of the choroid epithelial cell
  2. Choroid epithelial cells secrete fluid into the ventricle

Slide 19-20 lecture 3

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13
Q

What are the 2 steps of the net secretion of Na from the plasma to cerebrospinal fluid?

A
  1. Na-K pump in choroid plexus epithelia apical membrane moves Na out of the cell into the cerebrospinal fluid
  2. Active movement of Na out of cell generates inward Na gradient across basolateral membrane, energizing basolateral Na entry through Na-H exchange and Na-coupled HCO3 transport

Slide 19-20 lecture 3

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14
Q

How is the cerebrospinal fluid circulated?

7 steps

A
  1. Lateral ventricles
  2. Interventricular foramina of Monro
  3. Third ventricle
  4. Cerebral aqueduct of Sylvius
  5. Fourth ventricle
  6. Foramina of Magendie and Luschka
  7. Subarachnoid space, central canal of SC, over SC, over convexity of brain

Slide 21 lecture 3

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15
Q

How is the cerebrospinal fluid absorbed?

A

CSF is absorbed by the dural venous sinuses (particularly the superior sagittal sinus) through arachnoid granulations

Arachnoid granulations- a diverticulum of subarachnoid space
These act as pressure-sensitive, one-way valves for bulk CSF clearance (occurs when CSF pressure exceeds the venous pressure)

Slide 22-23 lecture 3

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16
Q

How does the rate of cerebrospinal fluid absorption change?

A

The rate of CSF formation is insensitive to changes in the pressure of CSF, while the absorption of CSF increased steeply as CSF pressures are above ~70mm H2O
This response results in a lower CSF volume and a tendency to counteract the increases intracranial pressure

Slide 24 lecture 3

17
Q

What is increased intracranial pressure (ICP)?

A

Increase in volume of brain tissue, blood, or CSF will produce increased ICP because cranium fixes volume
Increased ICP due to meningitis or an increase in volume of the brain produced by edema, tumor formation, a cerebral abscess, or hematoma
Severe elevated intracranial pressure can cause decreased cerebral flow and brain ischemia

Slide 25-26 lecture 3

18
Q

What is cerebral perfusion pressure?

A

Cerebral blood flow depends on cerebral perfusion pressure, which is defined as the mean arterial pressure minus the intracranial pressure

CPP= MAP - ICP

Slide 26 lecture 3

19
Q

What is papilledema?

A

Optic disc swelling that is secondary to elevated ICP
edema in area of optic disc caused by compression of retinal vein as it crosses the extension of the subarachnoid space to enter the optic nerve and axoplasmic flow stasis

Slide 27 lecture 3

20
Q

What is hydrocephalus?

A

“Water brain”
Abnormal increase in amount of cerebrospinal fluid within the ventricles of the brain

Obstructive CSF circulation interference
Loss motor function from white matter destruction
Something doesn’t let cerebrospinal fluid nicely escape

Slides 28-29 lecture 3

21
Q

What is a lumbar puncture?

A

Spinal tap
Composition of cerebrospinal fluid may be altered by diseases states
Grossly bloody or yellow, blood pigments etc could be seen in it so use lumbar puncture to see cerebrospinal fluid

Slide 30 lecture 3

22
Q

What are the 3 main sites barrier sites are located in the CNS?

A
  1. The brain endothelium forming the blood-brain barrier (BBB)
  2. The arachnoid epithelium forming the middle layer of the meninges
  3. The choroid plexus epithelium which secretes cerebrospinal fluid (CSF)

At each site, the physical barrier is caused by tight junctions that reduce the permeability of the paracellular pathway

Slide 32 lecture 3

23
Q

What is the blood brain barrier (BBB)?

A

Diffusion barrier impeded influx of most compounds from blood to brain
Essential for maintaining a constant internal environment

Endothelial cell right junctions prevents water soluble ions and molecules from passing from blood into the brain through paracellular route
Astrocyte endfeet provide a continuous covering of the capillaries and facilitate transport of substances between these cells and blood

Slide 33 lecture 3

24
Q

What are the 3 transmembrane proteins that make up the right junctions of the blood brain barrier?

A

Claudins
Occludins
Junctional adhesion molecules

Slide 34 lecture 3

25
Q

What are the 3 ways entry into the brain is achieved?

A
  1. Diffusion of lipid soluble substances
  2. Facilitative and energy-dependant receptor-mediated transport
  3. Ion channel and exchangers

Slide 35 lecture 3

26
Q

What is the neuromuscular unit?

A

Neuromuscular unit allows bidirectional communication between the microvasculature and neurons, with astrocytes playing intermediary roles

CSF follows routes of vessels

Slide 36-37 lecture 3

HSC 350 (10 decks)

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