19 - Blood Brain Barrier and CSF Flashcards
What are the 3 layers of the cerebral meninges?
Dura - attached to skull, hard
Arachnoid - trabecular meshwork , spiders web
Pia - thin tight membrane, attached to bl of brain
Where are blood vessels found in the meninges?
Dura and arachnoid
Where are veins found in the meninges?
Inner layers of the dura and crossing the dura-arachnoid interface
What are the 3 types of cerebral haemorrhage?
- Epidural haemorrhage: Bleeding outside the dura, arterial, no symptoms then mins/hours later severe headache as haematoma compresses brain
- Subdural haemorrhage: Bleeding between dura and arachnoid, bridging veins, slow onset of symptoms (24h), blood spread all over brain surface
- Subarachnoid hemorrhage: Bleeding in arachnoid space, ruptured aneurysm, arterial symptoms, sudden severe thunderclap headache. Form of stroke
What is the difference between a epidural and subdural bleed?
- Epidural bleed: Usually arterial, rapidly increases in size, lens shaped in MRI, acute skull trauma,
- Subdural bleed: Veins bridging dura and arachnoid, more spread out MRI, road accident which moves brain relative to skull, venous bleed so slower, symptoms may show up in minutes but can be delayed as much as 2 wks
What is the falx?
A sheet of dura which extends to divide the hemispheres
What are the tentoria?
Pair of transverse sheets of dura which extend below the base of the occipital cerebrum
They divide the cerebrum above from the cerebellum below
What is the gap between the two tentorii called?
Tentorial incisure
What is in the cerebral ventricles?
Cerebrospinal fluid
What is cerebrospinal fluid formed by?
Choroid plexus - a meshwork of capillaries covered by ependymal cells
What does choroid plexus do?
Produce a protein-free filtrate from blood
What rate is cerebrospinal fluid produced at?
500ml/day
What does healthy CSF contain?
Very little protein No cells (not pH buffered like blood)
How much CSF does the brain hold? Where is it drained into?
135-150ml
Drained into the blood through arachnoid granulations in the superior sagittal sinus
How much plasma proteins are there in CSF? How is this measured?
0.3 - 1.0% plasma proteins
Measured by lumbar puncture
What is the pressure of CSF?
4.4 - 7.3 mmHg (0.6 - 0.9kPa)
What is the flow of CSF?
Lateral ventricles - third ventricle - fourth ventricle - cisterna magna - subarachnoid space - absorbed in the arachnoid granulations - joins venous blood in sagittal sinus
What are arachnoid granulations?
Penetrate the dura at the top of the brain - enable CSF to drain into the superior sagittal sinus
Where is CSF found?
Subarachnoid space below the outer layer of arachnoid
What is hydrocephalus?
Accumulation of CSF in the ventricular system
Obstruction of normal CSF circulation due to blockage in cerebral aqueduct
Repaired by shunt
Detected by a translucent shunt as no brain matter to block light
What are the 2 types of cell in brain tissue? Which are most prevalent?
Neurones and Glia
Glia is most prevalent (80%)
Why are most tumours of the brain gliomas?
Neurons cannot divide (undergo mitosis)
What causes epilepsy?
Often caused by malfunction in glial cells
What are the 2 main types of glial cell and their functions?
Astrocytes - star shaped - maintain pH - secrete growth factors - form scar
Oligodendrocytes - schwann cells of the CNS
What are astrocyte end feet?
End of processes of astrocytes, function is not clear
Most of the free surface of neuronal dendrites and cell bodies - as well as axonal surfaces - covered with apposed astrocytic end feet
Every blood vessel in the CNS is jacketed by a layer of end feet that separate it from the neural tissue.
They form a continuous wall around the capillary
What is the tight junction system?
Barrier between blood and extracellular space of the brain
Tight junctions between endothelial cells lining cerebral capillaries
What is the Blood Brain Barrier?
Combination of astrocyte endfeet and endothelial cell tight junction
What can and cannot pass through the Blood Brain Barrier?
Cannot pass - macromolecules from entering or leaving CSF
Can - Due to special transport mechanisms, AA. lipid-soluble molecules - unaided so opiates (heroin) can cross the BBB and rapidly reach brain cells
What is the clinical significance of the BBB?
Prevents drugs such as antibiotics from reaching the brain
Meningitis - allows penicillin to enter brain
