10. CSF, BBB, ICP Flashcards
How much CSF is found in the sub-arachnoid space?
117ml
How much CSF is found in the ventricles?
23 ml
What are the functions of CSF?
Cushioning
Chemical stability
Allows brain to exist in neutral buoyancy
Where is CSF produced?
Choroid plexus
Around blood vessels and along ventricular walls
What is the structure of the choroid plexus?
2 cells thick: endothelial cells of capillary wall and ependema
Tight junctions in ependyma
What are the functions of the tight junctions in the ependyma?
Seals capillary walls to prevent unwanted substances entering CSF
Impermeable to water-soluble solutes, permeable to lipid soluble (these can dissolve in the cell membranes)
Dependable on transporters for water soluble
What is the difference in composition between the CSF and plasma?
In CSF:
more Na+ and Cl-
Less K+ and glucose
no protein
What forms the blood-CSF barrier?
Choroid plexus
Other brain capillaries
Transporters
What vertebral level is a lumbar puncture needle inserted into?
L3/4 or L4/5
What colour is CSF normally?
Colourless
What colour is CSF in a sub-arachnoid haemorrhage?
Yellow
What is the difference in a CSF sample from a patient with meningitis?
Increased WBCs
What is the difference in a CSF sample from a patient with multiple sclerosis?
Associated antibodies present
What is normal CSF/intercranial pressure?
10 mmHg
What is hydrocephalus?
Abnormal accumulation of CSF due to excessive production, obstruction in circulation or faulty reabsorption
Ventricles enlarge and brain is flattened against the skull
What conditions are associated with hydrocephalus?
Mental disability
Tunnel vision
Convulsive episodes
What are common causes of infantile hydrocephalus?
Stenosis or inflammation of aqueduct of sylvius
Spina bifida
What are common causes of adult hydrocephalus?
Obstruction of aqueduct
Obstruction of outflow from 4th ventricle
What is a contracoup injury?
Brain is driven against the opposite side of the skull to where a blow hits
What is a depressed skull fracture?
Bone is driven into brain tissue
What is the blood brain barrier made up of?
Walls of cerebral capillaries
Transporters
Astrocytes
How do brain capillaries differ to peripheral capillaries?
Lower permeability to water and impermeable to solutes due to BBB
In what case is the BBB often absent?
In blood vessels associated with tumours
Plasma proteins will enter ICF of brain tumours
What is the Monroe-Kellie doctrine?
Brain, brain fluid, blood and CSF are all incompressible
ICP is directly related to the volume of these contents
What are the symptoms of increased intercranial pressure?
Headache, nausea, restlessness
Neural dysfunction
Papilloedema
Cushing’s reflex
What is papilloedema?
Swelling of the optic disc
What triggers Cushing’s reflex?
Brain is severely hypercapnic and hypoxic
Triggers vasomotor centre in medulla
Give the steps of Cushing’s reflex?
- Peripheral vasoconstriction (reroute blood to brain)
- Results in increased BP (increase cerebral perfusion)
- Increased firing of baroreceptors
- Increased activity of cardio-inhibitory centre
Reflex bradycardia
