The Ventricular System

Question 1

what is the ventricular system

Answer 1

a series of CSF-filled interconnected spaces

continuous with subarachnoid space and central canal

Question 2

how do the ventricles develop?

Answer 2

neuroectoderm forms the neural tube the lumen of the neural tube becomes the ventricles and spinal canal
ependymal layer lines the ventricles and central canal

Question 3

which ventricle is associated with which brain area?

Answer 3

lateral ventricles - telencephalon
third ventricle - diencephalon
fourth ventricle - metencephalon
+cerebral aqueduct - mesencephalon

Question 4

what are the lateral ventricles?

Answer 4

two, very large 
one for each cerebral hemisphere 
horns/body correspond to to lobes of the hemisphere:
anterior horn: frontal lobe
body: parietal lobe
posterior horn: occipital lobe 
inferior horn: temporal lobe

Question 5

what are the borders of the lateral ventricles?

Answer 5

septum pellucidum separates ventricles
corpus callosum sits in roof
caudate nucleus sits in lateral wall
hippocampus sits in floor of inferior horn

Question 6

what is the interventricular foramen?

Answer 6

foramen of Monro

lateral ventricle communicate with the third ventricle through this

Question 7

what is the third ventricle?

Answer 7

slit-like clef between thalami

roof formed by fornix

Question 8

what is the cerebral aqueduct?

Answer 8

aqueduct of Sylvius
third ventricle communicates with the fourth ventricle through this
surrounded by midbrain

Question 9

what is the fourth ventricle?

Answer 9

rhomboid shape 
surrounded by hindbrain
cerebellum is posterior 
pons and medulla are anterior 
cerebellar peduncles are lateral 
continuous with central canal of spinal cord and subarachnoid space

Question 10

how does the fourth ventricle communicate with the subarachnoid space?

Answer 10

2 foramen of Luschka (lateral)
1 foramen of Magendie (middle)
into cisterna magna

Question 11

what is the choroid plexus?

Answer 11

present throughout ventricles
produces CSF
filters blood from branches of internal carotid and basilar arteries

Question 12

what is the structure of the choroid plexus?

Answer 12

simple - capillary network surrounded by cuboidal epithelium
tight junctions between epithelial cells

Question 13

what happens during CSF production?

Answer 13

blood is filtered through fenestrated capillaries
components are transported through the cuboidal epithelium into ventricles
tight junctions prevent macromolecules from entering CSF (forms blood-brain barrier)
permeable to water and CO2

Question 14

characteristics of he cuboidal epithelium

Answer 14

specialised ependyma
villi present to increase surface area
active transport of CSF components
bidirectional (uptake of metabolites into circulatory system)

Question 15

main differences between CSF and plasma concentration

Answer 15

lower [K+]
lower [Ca2+]
higher [Mg2+]
higher [Cl-]
lower glucose concentration 
much lower protein concentration

Question 16

how is CSF circulated?

Answer 16

passes from lateral ventricles through interventricular foramen to third ventricle
passes to fourth ventricle through cerebral aqueduct
enters cisterna magna through Luschka and Magende foramina
then passes over cerebellar/cerebral hemispheres or down dorsal spinal subarachnoid space and up ventral spinal subarachnoid space

Question 17

what is subarachnoid space?

Answer 17

lies between pia and arachnoid layers of meninges
follows contours of brain (gyru/sulci)
functionally important - ensures CSF is in contact with brain parenchyma
(transfer of micronutrients and removal of metabolites)

Question 18

what are arachnoid granulations?

Answer 18

herniations of arachnoid membrane (villi) through dura mater into venous sinuses
mainly within superior sagittal and transverse sinuses

Question 19

how is CSF absorbed?

Answer 19

arachnoic villi act as one-way valves
CSF pressure must exceed venous sinus pressure (tips close off to prevent blood reflux into subarachnoid space is venous pressure exceeds CSF)

Question 20

what is the volume of CSF?

Answer 20

500ml produced per day
total volume in system = 90-140ml
continuously moving, excess removed by arachnoid granulations

Question 21

what are the main functions of CSF?

Answer 21

hydraulic buffer to cushion brain against trauma
vehicle for removal of metabolites
stable ionic environment for neuronal function
transport of neurotransmitters and chemicals

Question 22

when is CSF yellow?

Answer 22

=xanthocromia
e.g. subarachnoid haemorrhage
lysis of red blood cells, haemoglobin is release and converted to bilirubin

Question 23

when is CSF cloudy?

Answer 23

e.g. mutliple sclerosis
protein content (gamma globulin) increase
e.g. bacterial meningitis
leukocytes are increased, indicative of infection

Question 24

how is CSF sampled?

Answer 24

taken my lumbar puncture
at lumbar cistern (no spinal cord present)
L3/4 in adults, L4/5 in children

Question 25

what is hydrocephalus?

Answer 25

dilation of brain ventricles
increased intercranial pressure
pressure on surrounding tissues affects neurological function

Question 26

what can cause hydrocephalus?

Answer 26

blocked CSF circulation, impaired absorption or over secretion
can be acquired or congenital

Question 27

symptoms of hydrocephalus

Answer 27

headache
vomiting
visual disturbances
papilledema (swelling of optic disc)
seizures 
altered cognition 
balance and coordination problems

Question 28

what is non-communicating hydrocephalus?

Answer 28

blockage within ventricular system
CSF does not circulate over surface of brain
ventricles are dilated
surgery: insert shunt to reduce intercranial pressure

Question 29

what can cause non-communicating hydrocephalus?

Answer 29

tumour, cyst, stenosis

Question 30

what is Dandy-Walker Syndrome?

Answer 30

congenital malformation of cerebellum
obstruction within foramina of fourth ventricle - symmetrical dilation of lateral, third and fourth ventricles
in infancy, child’s head may become enlarged

Question 31

what is communicating hydrocephalus?

Answer 31

obstruction in arachnoid villi

movement of CSF into venous sinuses is impeded

Question 32

what can cause communicating hydrocephalus?

Answer 32

impaired absorption following subarachnoid haemorrhage, trauma or bacterial meningitis