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Y2 LCRS Neuroscience and Mental Health > cerebral blood flow > Flashcards

cerebral blood flow Flashcards

cerebral blood flow: explain the importance of cerebral blood flow regulation, list the neural and humoral factors involved in regulation, explain the regulatory mechanisms in response to changes in blood pressure and carbon dioxide tension

1
Q

what happens when blood flow to brain is reduced by >50%

A

insufficient oxygen delivery, function becomes significantly impaired

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2
Q

what happens if total cerebral blood flow is interrupted for a) as little as 4 seconds, and b) after a few minutes

A

a) unconsciousness, b) irreversible damage occurs to brain

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3
Q

define syncope

A

fainting: common manifestation of reduced blood supply to brain

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4
Q

causes of syncope

A

hypotension, postural changes, vaso-vagal attack, sudden pain, emotional shock etc.

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5
Q

result of syncope

A

temporary interruption or reduction of blood flow to brain

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6
Q

what is the principal energy source of brain

A

glucose via blood

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7
Q

what % of the body’s glucose does the brain do

A

up to 50-60%

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8
Q

why does the brain use glucose

A

can’t store, synthesise or utilise any other source of energy; except in starvation where it metabolises ketones to a limited extent (CNS can adapt in chronic undernutrition)

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9
Q

common condition causing hypoglycaemia, and effects of hypoglycaemia

A

insulin-dependent diabetes (type 1); appear disorientated, slurred speech, impaired motor function

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10
Q

effect of [glucose] below 2nM

A

unconsciousness, coma, ultimately death

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11
Q

what mechanisms regulate cerebral blood flow

A

mechanisms affecting total cerebral blood flow, mechanisms relating activity to requirement in specific brain regions by altered localised blood flow

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12
Q

at what mean arterial blood pressure is total cerebral blood flow autoregulated

A

between approx. 60 and 160 mmHg

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13
Q

how is blood flow maintained

A

arteries and arterioles dilate or contract: stretch-sensitive cerebral vascular smooth muscle contracts at high blood pressure and relaxes at lower blood pressure

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14
Q

what happens below autoregulatory range

A

insufficient supply leads to compromised brain function

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15
Q

what happens above autoregulatory range

A

increased flow can lead to swelling of brain tissue which is not accomodated by “closed” cranium, increasing intracranial pressure

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16
Q

what determines O2 and glucose demands, and impact on autoregulation of blood supply

A

local brain activity, so must be local autoregulation

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17
Q

2 controls of local regulation of cerebral blood flow

A

neural, chemical

18
Q

what do branches of surface pial vessles do

A

penetrate brain parenchyma and enter the CNS tissue (penetrating artioles and penetrating venules)

19
Q

what do these branches of surface pial vessles branch to form, and function

A

capillaries which drain into venules and veins, then draining into surface pial veins

20
Q

features of CNS vascularisation

A

densely vascularised (no neurone more than 100um from a capillary)

21
Q

4 neural factors which regulate cerebral blood flow

A

sympathetic nerve stimulation, parasympathetic (facial nerve) stimulation, central cortical neurones, dopaminergic neurones

22
Q

sympathetic nerve stimulation: location and effect

A

to main cerebral arteries, producing vasoconstriction (probably only when high arterial blood pressure)

23
Q

parasympathetic (facial nerve) stimulation: effect

A

slight vasodilation

24
Q

what do central cortical neurones release

A

vasoconstrictor neurotransmitters e.g. catecholamines (e.g. adrenaline, noradrenaline)

25
Q

dopaminergic neurones: effect

A

vasoconstriction (localised effect relating to increased brain activity)

26
Q

what do dopaminergic neurones (local effect) innervate

A

penetrating arterioles and pericytes around capillaries, causing contraction/relaxation and subsequent diversion

27
Q

what are pericytes and what are their function

A

cells that wrap around capillaries; have diverse activities (e.g. immune function, transport properties, contractile)

28
Q

function of dopaminergic neurones

A

local effect: diversion of cerebral blood to areas of high activity

29
Q

effect of dopamine secreted by dopaminergic neurones

A

contraction of pericytes (in small vessels) via aminergic and serotoninergic receptors

30
Q

examples of localised chemical factors that regulate cerebral blood flow by causing vasodilation

A

most clinically relevant: CO2 (indirect), pH; also: NO, K+. adenosine, anoxia, kinins, prostaglandins, histamine, endothelins

31
Q

shape of pCO2 vs cerebral blood flow graph

A

sigmoid

32
Q

how does a high pCO2 cause vasodilation of cerebral arteries, increasing blood flow

A

CO2 is derived from neural metabolic activity and combines with water to form HCO3- and H+ (via carbonic anhydrase) in cells, then enters vascular smooth muscle cells/pericytes; CO2 in blood also diffuses into vascular smooth muscle cells/pericytes and combines with water to form H+ (via carbonic anhydrase); finally H+ in blood cannot cross the BBB; all of this causes a decrease in pH, causing relaxation of contractile smooth muscle cells, increasing blood flow

33
Q

imaging techniques because of local changes to cerebral blood flow

A

PET, functional MRI; increased neuronal activity = increased CO2 and subsequent H+ production = increased blood flow

34
Q

what produces CSF in brain and where

A

regions of choroid plexus in cerebral ventricles; protects brain

35
Q

CSF production: location and histology of cells

A

ependymal cells (epithelial-like glial cells, often ciliated) lining ventricles, aqueducts and canals, which in some regions of ventricles is modified to form branched villus structures (choroid plexus)

36
Q

formation of CSF in choroid plexus: characteristics of capillaries and local ependymal cells

A

leaky capillaries (enters plasma via arachnoid granulations), but local ependymal cells have extensive tight junctions; secrete CSF into ventricles which then circulates

37
Q

ventricles supplied by CSF via interventricular foramina

A

lateral and 3rd

38
Q

ventricles supplied by CSF via cerebral aquaduct from 3rd

A

4th

39
Q

pathway of CSF from 4th to circulation

A

into subarachnoid space via medial and lateral apetures

40
Q

CSF volume

A

80-150ml

41
Q

CSF functions

A

protection (physical and chemical), nutrition of neurones, transport of molecules

42
Q

why is it clinically important that CSF has little protein

A

if high could indicate bacterial infection or damage to CSF vessels

Y2 LCRS Neuroscience and Mental Health (79 decks)

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