The Ventricular System Flashcards
what is the ventricular system
a series of CSF-filled interconnected spaces
continuous with subarachnoid space and central canal
how do the ventricles develop?
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
which ventricle is associated with which brain area?
lateral ventricles - telencephalon
third ventricle - diencephalon
fourth ventricle - metencephalon
+cerebral aqueduct - mesencephalon
what are the lateral ventricles?
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
what are the borders of the lateral ventricles?
septum pellucidum separates ventricles
corpus callosum sits in roof
caudate nucleus sits in lateral wall
hippocampus sits in floor of inferior horn
what is the interventricular foramen?
foramen of Monro
lateral ventricle communicate with the third ventricle through this
what is the third ventricle?
slit-like clef between thalami
roof formed by fornix
what is the cerebral aqueduct?
aqueduct of Sylvius
third ventricle communicates with the fourth ventricle through this
surrounded by midbrain
what is the fourth ventricle?
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
how does the fourth ventricle communicate with the subarachnoid space?
2 foramen of Luschka (lateral)
1 foramen of Magendie (middle)
into cisterna magna
what is the choroid plexus?
present throughout ventricles
produces CSF
filters blood from branches of internal carotid and basilar arteries
what is the structure of the choroid plexus?
simple - capillary network surrounded by cuboidal epithelium
tight junctions between epithelial cells
what happens during CSF production?
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
characteristics of he cuboidal epithelium
specialised ependyma
villi present to increase surface area
active transport of CSF components
bidirectional (uptake of metabolites into circulatory system)
main differences between CSF and plasma concentration
lower [K+] lower [Ca2+] higher [Mg2+] higher [Cl-] lower glucose concentration much lower protein concentration
how is CSF circulated?
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
what is subarachnoid space?
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)
what are arachnoid granulations?
herniations of arachnoid membrane (villi) through dura mater into venous sinuses
mainly within superior sagittal and transverse sinuses
how is CSF absorbed?
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)
what is the volume of CSF?
500ml produced per day
total volume in system = 90-140ml
continuously moving, excess removed by arachnoid granulations
what are the main functions of CSF?
hydraulic buffer to cushion brain against trauma
vehicle for removal of metabolites
stable ionic environment for neuronal function
transport of neurotransmitters and chemicals
when is CSF yellow?
=xanthocromia
e.g. subarachnoid haemorrhage
lysis of red blood cells, haemoglobin is release and converted to bilirubin
when is CSF cloudy?
e.g. mutliple sclerosis
protein content (gamma globulin) increase
e.g. bacterial meningitis
leukocytes are increased, indicative of infection
how is CSF sampled?
taken my lumbar puncture
at lumbar cistern (no spinal cord present)
L3/4 in adults, L4/5 in children
what is hydrocephalus?
dilation of brain ventricles
increased intercranial pressure
pressure on surrounding tissues affects neurological function
what can cause hydrocephalus?
blocked CSF circulation, impaired absorption or over secretion
can be acquired or congenital
symptoms of hydrocephalus
headache vomiting visual disturbances papilledema (swelling of optic disc) seizures altered cognition balance and coordination problems
what is non-communicating hydrocephalus?
blockage within ventricular system
CSF does not circulate over surface of brain
ventricles are dilated
surgery: insert shunt to reduce intercranial pressure
what can cause non-communicating hydrocephalus?
tumour, cyst, stenosis
what is Dandy-Walker Syndrome?
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
what is communicating hydrocephalus?
obstruction in arachnoid villi
movement of CSF into venous sinuses is impeded
what can cause communicating hydrocephalus?
impaired absorption following subarachnoid haemorrhage, trauma or bacterial meningitis
