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neuro > CSF & intracranial pressure > Flashcards

CSF & intracranial pressure Flashcards

1
Q

where is CSF located

A

between the ventricles and subarachnoid space

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2
Q

2 main types of meninges

A
  • dura mater (pachymeninges)
  • leptomeninges
    - arachnoid
    - pia
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3
Q

CSF production and the process involved

A

mostly produced by the choroid plexus
-mainly in lateral ventricles

involves 2 processes

  • ultrafiltration across choroidal capillary wall
  • active secretion by choroidal epithelium
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4
Q

choroid plexus structure

A
  • fenestrated capillary network surrounded by a row of epithelial cells
  • choroid plexus epithelial cells have tight junctions between them. They contain vesicles and lysosomes and have a microvilli brush border
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5
Q

CSF circulation

A
  1. CSF produced in lateral ventricles
  2. travels trough foramina munro
  3. goes into the midline of the 3rd ventricle
  4. passes through the sylvian aqueduct into 4th ventricle
  5. then leaves out through 3 foramen into subarachnoid space
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6
Q

CSF absorption

A

majority via the small arachnoid villi and larger arachnoid granulations
(herniations of arachnoid mater through dura into superior sagital sinus)

absorb CSF by unidirectional ‘bulk flow’

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7
Q

CSF total volume

A

150ml
mostly in subarachnoid space
(some in ventricles)

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8
Q

rate of CSF production

A

600ml/day

0.35ml/min

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9
Q

what does CSF absorption depend on

A

hydrostatic pressure in subarachnoid space

- not regulated by any transport process

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10
Q

CSF composition

A

clear and colourless

  • WBC <5x10^6/L
  • no neutrophils
  • no RBC
  • protein <0.45g/L
  • glucose >2.5mmol/l
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11
Q

CSF changes in meningitis

A

increase WBC
increase protein
some cause low glucose (bacterial meningitis)

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12
Q

CSF in subarachnoid haemorrhage

A

increase in RBC

‘xanthochromia’ (yellow discolouration due to RBC breakdown - takes time)

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13
Q

CSF function

A

maintains environment for neurons and glia

mechanical cushion for brain

counters sudden increases in intracranial pressure

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14
Q

function of the BBB

A
  1. regulation of ionic balance in brain
  2. facilitates transport of essential substrates into brain e.g. oxygen
  3. barrier against the entry of potentially harmful molecules

metabolites need to be selectively transported across the endothelial cells

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15
Q

what does the BBB consist of?

A
  • specialised endothelial cells
  • thick basement membranes
  • astrocytic processes on capillaries
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16
Q

describe the differences between systemic endothelial cells and brain endothelial cells

A

intracellular junctions

  • systemic = fenestrated
  • brain = tight

pinocytotic vesicles

- systemic = common
- brain = uncommon

basement membrane

 - systemic = thin
 - brain = thick

mitochondria

  - systemic = +
  - brain = +++
17
Q

transport across BBB

A

diffusion
-lipid soluble substances e.g.O2/CO2

active transport

  • energy dependent
  • glucose, some AA, vitamins

ion channels

18
Q

factors affecting passage of molecule across BBB

A
  1. molecular weight (size)
  2. lipid solubility
  3. ionisation
  4. protein binding
  5. transport mechanism
19
Q

disease processes involving the BBB

A
  • disruption of tight junctions
  • disruption of BM
  • disruption of endothelial-astrocyte interaction
  • altered function of specific transporter
  • new BVs lacking features of BBB
20
Q

how does meningitis affect the BBB

A

inflammatory response causes BBB breakdown

white cells and protein in the CSF

21
Q

how do brain tumours affect the BBB

A
  • abnormal BVs
  • vessels can be ‘leaky’
  • interstitial fluid accumulates (oedema)
22
Q

how is intracranial pressure measured

A
  • lumbar puncture

- intracranial pressure monitoring

23
Q

normal CSF pressure

A

= 65-195mm of CSF (or water)

= 5-15mmHg

24
Q

what are the 3 components of the intracranial contents and there values

A

brain 1300-1500mL
blood 75mL
CSF 75mL

intracranial volume fixed by skull

25
Q

what is the Monro-Kellie doctrine concept

A

if you increase the volume of one intracranial component you must decrease another component.
If not ICP increases

26
Q

compensatory mechanisms if ICP increases

A
  • CSF displaced into SC
  • cerebral veins collapse/compress
  • increase in CSF absorption
  • lumbrosacral dura distensible
27
Q

causes of increased ICP

A

increase in volume of brain tissue
- e.g. tumour or oedema

increase in volume of CSF (hydrocephalus)
- obstruction or decreased absorption

increase in cerebral blood volume
- obstruction of venous outflow or loss of autoregulation

28
Q

cushing’s signs and mechanism

A

cushings triad

  1. arterial hypertension
  2. slow HR
  3. slow RR

mechanism
- reduction in BF to medulla (due to direct distortion)

29
Q

cerebral herniations

A

displacement of brain tissue:

  - from one intracranial compartment to another
  - through foramen magnum into SC

midline shift

can cause compression of:

  • brain
  • cranial nerves
  • BVs
30
Q

transtentorial herniation

A

herniation of medial temporal lobe through tentorial notch

causes compression of midbrain, oculomotor nerve, posterior cerebral artery

31
Q

tonsillar herniation

A

herniation of inferior cerebellum into SC (‘cerebellar tonsils’)

32
Q

what does cerebral perfusion pressure depend on

A

mean arterial pressure and intracranial pressure

CPP = MAP - ICP

33
Q

what does cerebrovascular autoregulation maintain

A

a constant cerebral BF over a wide range of cerebral perfusion pressures

34
Q

what happens when there is a loss of cerebrovascular autoregulation (pressure outside of 60-150mmHg)

A

cerebral BF is proportional to arterial BP

35
Q

what mediates the constriction and dilation of small cerebral arteries

A

vasoactive factors released by neurons

36
Q

factors affecting ICP

A
  • arterial BP
  • increased venous pressure = increased ICP
  • increased intrathoracic P increased venous P
  • posture (lying, increases venous P)
  • increased PaCO2 or decreased PaO2 = increased ICP
  • decreased temp causes decreased ICP
37
Q

why is the BBB important for neurons

A

provides a stable environment in which they can function

neuro (20 decks)

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