cerebral circulation, blood flow, BBB, and CSF formation Flashcards
what are the four major blood vessels that go to the brain?
2 vertebral arteries - to basilar artery
internal carotid artery - middle and anterior cerebral branches
where does the spinal cord get its circulation?
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
where does blood supply for the ear come from?
labyrinth artery which often branches off of the anterior cerebellar artery?
what is a common result of posterior cerebral artery stroke?
vision loss
where does the middle cerebral artery travel?
lateral fissure - supplies superior gyrus of temporal lobe and much of lateral hemisphere
where does the anterior cerebral artery travel? what does it supply?
above corpus callosum under/between cingulate gyri
supplies frontal lobe
what are watersheads?
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
what factors regulate cerebral blood flow? (list)
1: autoregulation - capillaries contain pericytes - also through myogenic reflex - sense pressures
2: chemical mechanisms (CO2 reactivity, metabolic coupling)
3: neuronal control
4: blood viscosity
what are the factors affecting blood viscosity?
hematocrit
red cell aggregation and flexibility
plasma protein concentrations
what is the nervous control of the CBF?
extrinsic nerves from superior cervical ganglia, sphenopalatin ganglia, trigeminal ganglia
interneurons or central pathways from locus ceruleus (norepi), raphe (5-HT), nucleus basalis (AcTH)
how does high blood pressure affect CBF?
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
what is hypertensive encephalopathy?
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
what is hyperperfusion syndrome?
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
how does CO2 affect CBF?
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
what is the monro-kellie doctrine?
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
how does ICP affect CBF?
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
what is the cushing reflex?
if pressure in side the head goes up a lot, get increased arterial pressure, but heart rate goes down because of increased vagal pressure
how does metabolism affect CBF?
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
how is the BBB formed?
astrocytes signal to capillary endothelial cells that they should form tight junctions
what can diffuse across the BBB?
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
how do non-lipid soluble substrates cross the BBB?
facilitated diffusion usually
ion trasport by pumps - tightly regulated
what are the reasons that an area would not have a BBB?
to sense things
to get stuff out of the brain - eg median eminence
what is the importance of tanicytes?
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)
describe the blood CSF barrier.
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
what parts of the brain does the iCA supply?
frontal, parietal and temporal lobes
what do the vertebral arteries supply?
temporal and occipital lobes, midbrain, hindbrain
what are the branches of the ICA?
carotid siphon - opthalmic, posterior communicating, anterior choroid
posterior communicating to posterior cerebral
terminates in anterior and middle cerebral arteries
where does the anterior choroid artery travel?
posteriorward along optic tract and enters choroid fissure - gives numerous small branches to interior of brain, including choroid plexus and lateral ventrical
what are the branches of the basilar artery?
distributed to pons, cerebellum, internal ear, midbrain, cerebral hemispheres
anterior inferior cerebellar arteries
paired labyrinthe
superior cerebellar arteries
posterior cerebral arteries = terminal branches
where do the AICA go and what do they supply?
pass dorsally on inferior surface of cerebellum
supply cerebellum and pons
where do the superior cerebellar arteries go and what do they supply?
laterally just inferior to the oculomotor and trochlear nerves
to cerebellum
what do the posterior cerebral arteries supply?
medial temporal and most of occipital lobes
what are lateral lacunae? from wehre do they receive fluid?
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
