The Ventricular System & Circulation of CSF Flashcards
Ventricles:
- are
- derived from
- purpose
- small cavity/chamber
- derived from the expansion and
folding of the neural plate - to produce and distribute CSF
Ventricles Embryology:
The neural tube is formed as it
detaches from the epiblast = neurulation
The neural crest cells seal the remaining space at the cranial and caudal ends are called the neuropores
If the pores do not seal causes congenital abnormalities
What cells develop into the PNS?
What cells develop into the CNS?
- neural crest cells detach and create
the PNS - the neural tube creates the CNS
Formation of Brain Vesicles:
neural tube starts to expand into three balloons at the top (prosencephalon, mesencephalon and rhombencephalon)
the three balloons then develop into 5 different components, which then fold in on themselves to create the brain
the rest of the tube forms the spinal cord
Brain Flexures:
the five different components fold in on themselves: in the brain we have the cerebral hemispheres on top, then the midbrain and then the cerebellum
forms different flexures: midbrain flexures, pontine flexure
(hollow cavity)
Lateral ventricles are next to which parts of the brain
telencephalon and prosencephalon
Aquaduct is
the ventricular system near midbrain
Central Canal:
hole in the middle of the spinal cord
Foramen of Monroe are
2 holes that divide the lateral ventricles
INTERVENTRICULAR
Foramen of Magendie and Foramen of Luschka
foramina connect the interventricular system so that CSF can leave the sealed structure
The Ventricular Pathway:
The Ventricular Pathway:
Dandy-Walker Malformation:
- developmental problem with
ventricular system resulting in an
expanded fourth ventricle
Dandy-Walker Malformation:
What cells line ventricles?
Choroid cells = specialised ependymal cells
Ependymal cells = specialised glial cells
Choroid Cells:
- function
to produce cerebrospinal fluid (CSF)
Where does the majority of choroid cells lie?
The lateral ventricles
What allows contact of CSF with brain cells?
leaky lining?
***Choroid plexus:
network of choroid cells with capillaries
Draw choroid plexus:
Label diagram on addendum A
Choroid plexus
one confluent tube system
Formation of CSF:
insert diagrams
First diagram blue = ventricles
green = ependymal cells
Second diagram shows fenestrated capillaries allowing substances to seep out into the extracellular space
in order for molecules to move from outside of capillaries and into CSf they have to pass through the choroid cells
they can not pass between the choroid cells because the choroid cells have tight junctions
Channels in choroid cells allow substances to pass into CSF.
Choroid cells also contain carbonic anhydrase which breaks down water into CO2 and H2
creates an acid, which can act as a buffer
What is the composition of CSF determined by?
the channels the choroid cells possess
Drugs that impact the kidneys can impact the brain
because channels found in cells lining kidney are same/similar to those found in choroidal cells
CSF Production Cellular Level:
Water is broken down into bicarb which is pushed over by opposite flow of Na+ and K+
Creates fluid
Drugs that inhibit carbonic anyhydrase results in
alteration of CSF production (slows down)
CSF:
- is
- looks
- how much produced a day?
- means
- normal CSF pressure
- function
- specialised version of blood
- clear and colourless
- 500ml per day, only need 150ml
- rate of production = rate of
reabsorption (high turnover results
in efficient waste disposal) - 5-18cmH2O
- offers mechanical and chemical
protection
CSF vs Plasma table
The Blood Brain Barrier:
- function
- formed by
- areas that lack BBB
- hence
- protects the brain from rapid shifts
in electrolytes and metabolities - formed by tight junctions
- choroid plexus and circumventricular
organs (like pineal gland) lack a BBB - circumventricular organs are directly
exposed to blood solutes ->
neuroendocrine control
Blood Brain Barrier:
capillaries inside the brain are unfenestrated
three different aspects:
- thick basement membrane
- tight junctions between cells
- astroctyes are a different glial cells
which seal off the capillary hence
offer a protective mechanism to the
brain and are involved in cell
signalling
CSF Circulation:
CSF circulates in the ventricular system
three hollow tubes that allow CSF to travel into meningeal layers
between the pia mater and arachnoid mater hence in the sub-arachnoid space
fluid bathes brain in the sub-arachnoid space
***arachnoid granulations are outpouchings from the arachnoid layer into the dural layers, allowing waste products to travel into the venous system via the dural venous sinus
- The CSF passes
from the lateral
ventricles to the
third ventricle
through the
interventricular
foramen (of Monro). - From the third
ventricle, the CSF
flows through the
cerebral aqueduct
(of Sylvius) to the
fourth ventricle. - From the fourth
ventricle, some CSF
flows through a
narrow passage
called the obex and
enters the central
canal of the spinal
cord. However, the
majority of CSF
passes through the
apertures of the
fourth ventricle; the
median aperture (of
Magendie) and two
lateral apertures (of
Luschka). Via these
openings, the CSF
enters the cisterna
magna and
cerebellopontine
cisterns,
respectively. - From there, the CSF
flows through the
subarachnoid space
of the brain and
spinal cord. - It is finally
reabsorbed into the
dural venous
sinuses through
arachnoid
granulations.
CSF Cisterns and the Venous System:
CSF Cistern:
- pools of CSF in larger spaces
- eg pre-pontine cistern
CSF Venous System: end-point:
All dural venous sinuses drain into the sigmoid sinuses which drain into the internal jugular vein, which combines with the subclavian veins to form the brachiocephalic veins which combine to form the superior vena cava at T4/5
Glymphatic System
Arteries in the brain dive down into the brain, penetrating arteries creates a space between the tissue and and the vessels
move from periarterial to the perivenous space and then into venous sinuses
**occurs through channels called aquaporin 4 channels and through force/connective flow
Problems with CSF Circulation:
- higher pressure:
- blockage of flow (stenosis,
thrombosis)
- overproduction (choroid plexus
papilloma)
- reduced reabsorption (neoplasm) - lower pressure:
- leak (trauma/spina tap) causing
brain sag
Hydrocephalus:
insert diagram
- fluid on the brain
- two types:
- communicating (no problem with
the hydrocephalus) - non-communicating = blockage
- communicating (no problem with
Hydrocephaly on CT:
- fluid expands, squashes brain
because brain is sealed - in child head is still moldable as it is
growing, lateral ventricles will
expand, makes the skull expand =
make sure head circumference is
correct
Treatment of Hydrocephaly:
- drugs that inhibit carbonic
anhydrase (not very fast) - surgical intervention = put a tube in
ventricles to remove some fluid, add
tube down into peritoneum =
ventriculo-peritoneal shunt
Lumbar Puncture:
- diagnostic tool
- into cauda equina (around L3/4/5)
CSF Analysis:
Environment of the brain and spinal cord is protected by CSF both mechanically and chemically.
bouyancy
nutrients
