Lecture 8 9/5/23 Flashcards
What are the characteristics of normal cerebrospinal fluid?
-clear and colorless
-small amount of protein
-few lymphocytes
-very similar to water
How can disease impact CSF?
increase the amount of protein and/or lymphocytes in the fluid
What are the ventricles in the brain?
-2 lateral
-3rd
-4th
What structure allows the 3rd ventricle to drain into the 4th ventricle?
mesencephalic aqueduct
What is the role of the lateral apertures of the 4th ventricle?
allow CSF to drain into the sub-arachnoid space
If the CSF doesn’t drain from the 4th ventricle into the sub-arachnoid space, where does it go?
central canal of the spinal cord
What is the function of the choroid plexus?
produce CSF
What are the characteristics of CSF production?
-occurs in each ventricle
-by-product of brain metabolism
-constant production
-involves active transport of Na+ (needs energy!)
How does the choroid plexus produce CSF?
-choroid plexus is very vascular
-blood flows into choroid plexus and is filtered
-excess serum fluid becomes CSF
Which enzyme is involved in CSF production?
carbonic anhydrase
How does the CSF flow?
-rostrally to caudally
-from lateral ventricles, to 3rd ventricle, to 4th ventricle and out
What causes the CSF to flow?
pulsation of blood in the choroid plexus with each heart beat
Where is CSF reabsorbed?
in the sub-arachnoid space
What structures allow for reabsorption of CSF?
arachnoid villi
How do arachnoid villi allow for reabsorption of CSF?
-arachnoid villi protrude up into venous sinus
-when pressure increases, villi act as one way valve and allow CSF out into bloodstream
-one way valve prevents blood flow into CNS
What are the functions of CSF?
-cushion the brain
-pressure regulation
-source of nourishment/waste removal
-chemical buffer
What is hydrocephalus?
dilation/enlargement of ventricular system caused by obstruction of CSF flow
Why do toy breeds often present with an “enlarged head?”
-they have a genetic brain malformation causing a CSF flow blockage
-enlarged ventricles prevent skull sutures from closing properly
What are the clinical signs of hydrocephalus?
-behavior changes
-ataxia
-seizures
-altered mentation
-enlarged, dome-shaped skull
-persistent fontanelle/soft spots
What is a ventriculoperitoneal shunt?
-a tube that inserts into the ventricular system and the abdomen to drain CSF
-one-way valve on the tube allows for drainage when pressure is too high
Why can sulci not be seen on MRI in an animal with hydrocephalus?
the pressure from the dilated vesicles presses on the CSF in the sulci and prevents them from being seen on MRI
What is the blood-brain barrier?
selective barrier between systemic circulation and central nervous system
Why does the BBB exist?
there is a lot of stuff in blood that we do not want to allow into the CNS
What are the components of the BBB?
-tight junctions between the cells of the capillary walls
-thick basement membrane surrounding endothelial cells
-layer of foot processes from astrocytes providing extra support
What substances is the BBB highly permeable to?
-water
-CO2
-O2
-most lipid soluble substances
What substances is the BBB slightly permeable to?
electrolytes
What substances are unable to permeate the BBB?
-plasma proteins
-most non-lipid soluble and/or large organic molecules
Why is the permeability of the BBB an issue when treating infections?
the BBB does not let therapeutic levels of some antibiotics enter the CNS
What happens when proteins enter the brain during infection/tumor?
-the proteins pull water with them
-leads to brain swelling
What areas of the brain lack the BBB?
-hypothalamus
-area postrema
-pineal gland
-choroid plexus
Why do some areas of the brain lack the BBB?
in order to monitor what is going on in the blood and respond accordingly
How is CSF collected for testing?
spinal tap
