cerebral circulation, blood flow, BBB, and CSF formation

Question 1

what are the four major blood vessels that go to the brain?

Answer 1

2 vertebral arteries - to basilar artery

internal carotid artery - middle and anterior cerebral branches

Question 2

where does the spinal cord get its circulation?

Answer 2

on ventral side, anterior spinal artery - runs length of spinal cord in midline - supplemented periodically by arteries running on nerve roots
two posterior spinal arteries dorsally - come off of posterior cerebral arteries? - also get supplemented

posterior supply dorsal horn and dorsal columns - anterior supplies everything else

posterior spinal less likely to be compromised because there’s two of them

Question 3

where does blood supply for the ear come from?

Answer 3

labyrinth artery which often branches off of the anterior cerebellar artery?

Question 4

what is a common result of posterior cerebral artery stroke?

Answer 4

vision loss

Question 5

where does the middle cerebral artery travel?

Answer 5

lateral fissure - supplies superior gyrus of temporal lobe and much of lateral hemisphere

Question 6

where does the anterior cerebral artery travel? what does it supply?

Answer 6

above corpus callosum under/between cingulate gyri

supplies frontal lobe

Question 7

what are watersheads?

Answer 7

follow one blood vessel out to the end until you meet the vessel from the other side (ie follow a deep vessel until it meets a superficial vessel) - that area’s the most susceptible to O2 deprivation so most likely to be damaged
between the deep structures (which are supplied by deep vessels) and more superficial structures (which are supplied by superficial vessels) - ie these areas get the end of the blood supply from both ends

Question 8

what factors regulate cerebral blood flow? (list)

Answer 8

1: autoregulation - capillaries contain pericytes - also through myogenic reflex - sense pressures
2: chemical mechanisms (CO2 reactivity, metabolic coupling)
3: neuronal control
4: blood viscosity

Question 9

what are the factors affecting blood viscosity?

Answer 9

hematocrit
red cell aggregation and flexibility
plasma protein concentrations

Question 10

what is the nervous control of the CBF?

Answer 10

extrinsic nerves from superior cervical ganglia, sphenopalatin ganglia, trigeminal ganglia

interneurons or central pathways from locus ceruleus (norepi), raphe (5-HT), nucleus basalis (AcTH)

Question 11

how does high blood pressure affect CBF?

Answer 11

autoregulatory curve changes - blood vessels adapts - means shouldn’t lower people’s blood pressure quickly because blood in brain would be changed too fast and brain wouldn’t get enough O2

Question 12

what is hypertensive encephalopathy?

Answer 12

blood pressure exceeds upper limit of autoregulation
passive increases in CBF occur with resulting cerebral edema and/or hemorrhage
clinical picture involves headache, altered level of consciousness, seizures, and potentially death
BBB can be damaged

Question 13

what is hyperperfusion syndrome?

Answer 13

sudden return of normal flow in a cerebral vascular bed which has had chronically low perfusion
may result in cerebral edema, seizures, and/or hemorrhage

occurs, for example, if there was a blockage that gets loosened or removed

Question 14

how does CO2 affect CBF?

Answer 14

direct correlation between PCO2 and CBF (acid/base balance in the blood)
increased pCO2 causes vasodilation
decreased pCO2 causes vasoconstriction
probably pH mediated

pCO2 also directly related to intracranial blood volume

Question 15

what is the monro-kellie doctrine?

Answer 15

essentially say that the space the brain is in is a closed space…

intracranial blood volume is fixed and = brain volume + CSF + blood volume
- if any of these increase, intracranial pressure (ICP) will go up

means that masses take up space and will increase ICP - squeeze out fluid and compromise circulation

Question 16

how does ICP affect CBF?

Answer 16

perfusion pressure = mean arterial pressure -ICP
hyperventilation decreases blood volume (and ICP) by vasoconstriction - but also increases resistance to flow
increased mean arterial pressure improves flow

Question 17

what is the cushing reflex?

Answer 17

if pressure in side the head goes up a lot, get increased arterial pressure, but heart rate goes down because of increased vagal pressure

Question 18

how does metabolism affect CBF?

Answer 18

gray matter metabolic activity is higher than white matter - CBF is therefore greater in gray matter

CBF is correlated to the metabolism of one or several vasoactive metabolites including adenosine, acid, prostaglandins, glutamate, NO
these can be produced by neurons and/or glia

Question 19

how is the BBB formed?

Answer 19

astrocytes signal to capillary endothelial cells that they should form tight junctions

Question 20

what can diffuse across the BBB?

Answer 20

things that are very lipid soluble (nicotine, ethanol, diazepam (valium), heroin)
large things and things bound to protein in the blood don’t cross
H2O via simple diffusion

Question 21

how do non-lipid soluble substrates cross the BBB?

Answer 21

facilitated diffusion usually

ion trasport by pumps - tightly regulated

Question 22

what are the reasons that an area would not have a BBB?

Answer 22

to sense things

to get stuff out of the brain - eg median eminence

Question 23

what is the importance of tanicytes?

Answer 23

in areas without a BBB, still need some sort of barrier
these cells isolate the circumventricular organs from the ventricles and the rest of the brain (so basically separate the areas that don’t have a BBB from those that do)

Question 24

describe the blood CSF barrier.

Answer 24

takes place at choroid plexus - capillaries inside choroid plexus leaky (like in rest of body)
choroid plexus cells derived from epidemyal cells - keep blood from getting into CSF and visaversa

Question 25

what parts of the brain does the iCA supply?

Answer 25

frontal, parietal and temporal lobes

Question 26

what do the vertebral arteries supply?

Answer 26

temporal and occipital lobes, midbrain, hindbrain

Question 27

what are the branches of the ICA?

Answer 27

carotid siphon - opthalmic, posterior communicating, anterior choroid
posterior communicating to posterior cerebral
terminates in anterior and middle cerebral arteries

Question 28

where does the anterior choroid artery travel?

Answer 28

posteriorward along optic tract and enters choroid fissure - gives numerous small branches to interior of brain, including choroid plexus and lateral ventrical

Question 29

what are the branches of the basilar artery?

Answer 29

distributed to pons, cerebellum, internal ear, midbrain, cerebral hemispheres
anterior inferior cerebellar arteries
paired labyrinthe
superior cerebellar arteries
posterior cerebral arteries = terminal branches

Question 30

where do the AICA go and what do they supply?

Answer 30

pass dorsally on inferior surface of cerebellum

supply cerebellum and pons

Question 31

where do the superior cerebellar arteries go and what do they supply?

Answer 31

laterally just inferior to the oculomotor and trochlear nerves
to cerebellum

Question 32

what do the posterior cerebral arteries supply?

Answer 32

medial temporal and most of occipital lobes

Question 33

what are lateral lacunae? from wehre do they receive fluid?

Answer 33

venous meshworks within the dura near the superior sagittal sinus
sources:
1: emissary veins from scalp
2: diploic veins from marrow of the skull bones
3: menigeal veins
4: occasionally some cerebral veins