The ventricular system Flashcards
What is the ventricular system?
Series of CSF-filled interconnected spaces
Continuous with the subarachnoid space and central canal
How do the ventricles develop?
From the lumen of the neural tube
Lumen expands at cranial end
Ventricles associated with each part of the brain
Name the ventricles
Lateral ventricles Third ventricle Cerebral aqueduct Fourth ventricle Central canal
Describe the lateral ventricles
Two ventricles - very large
One for each cerebral hemisphere
Body, anterior, posterior and inferior horn corresponding to lobes of the hemispheres
What separates the lateral ventricles?
Septum pellucidum
What is a T1 weighted MRI
Fluid appears black
Good for structure
What is a T2 weighted MRI
Fluid appears white
Good for fluid
What sits in the roof of the lateral ventricle?
Corpus callosum
What sits in the lateral wall of the lateral ventricles?
Caudate nucleus
What sits in the floor of the inferior horn?
Hippocampus
How do the lateral ventricles communicate with the third ventricle?
Through the interventricular foramen (also called foramen monro)
Where is the third ventricle located?
Slit like cleft between thalami
What forms the roof of the third ventricle?
Fornix
How do the third and fourth ventricles communicate?
Through cerebral aqueduct (aqueduct of sylvius)
What is the fourth ventricle surrounded by?
Hindbrain
Cerebellum posterior
Pons and medulla anterior
Cerebellar peduncles lateral
Describe the shape of the fourth ventricle
Rhomboid shape
What is the fourth ventricle continuous with?
Continuous with the central canal of the spinal cord and subarachnoid space
Name the three foramen which exit into the subarachnoid space
- Two Foramen of Luschka (lateral)
- One Foramen of Magendie (middle)
What do the 3 foramina communicate with?
Cisterna Magna
What produces CSF?
Choroid plexus
What does the choroid plexus do?
Filters blood from branches of internal carotid and basilar arteries
Where is the choroid plexus found?
Throughout the ventricles
What is the structure of the choroid plexus?
Capillary network surrounded by cuboidal epithelium
Tight junctions between epithelial cells - prevents macromolecules from entering CSF- forms blood brain barrier. Permeable to water and CO2
What happens during CSF production?
Blood filtered through fenestrated capillaries
Components transported through cuboidal epithelium into ventricles
Describe the cuboidal epithelium
Specialized ependyma
Villi increase surface area
Active transport of CSF
Bidirectional
What proportion of CSF is produced in the ventricles?
60%
Why do the ionic compositions of plasma and CSF differ?
Regulation by active transport
Ideal for physiological functioning of neurons
What is the main major difference between CSF and plasma?
Hardly any protein
Describe CSF circulatory pathway
Lateral ventricles
Third ventricle
Fourth ventricle
Cisterna magna (subarachnoid space)
Down doral spinal subarachnoid space and up ventral spinal subarachnoid space
Over cerebral hemispheres into arachnoid granulations
or over cerebellum/cerebral hemispheres
Where is the subarachnoid space found?
Lies between pia and arachnoid
Follows contours of the brain
How is the subarachnoid space functionally important?
In contact with brain parenchyma
- Transfer of micronutrients into brain
- Removal of metabolites
What are the arachnoid granulations?
Herniations of the arachnoid membrane through dura mater into venous sinuses
Mainly within the superior sagittal and transverse sinuses
How is CSF absorbed?
CSF pressure must exceed that in venous sinuses
If venous pressure exceeds CSF pressure the tips of villi close off and prevents reflux of blood into the subarachnoid space
Arachnoid villi act as one-way valves
How much CSF is produced each day?
500 ml
What is the total volume in the system?
90-140 ml constantly moving and excess is absorbed by arachnoid granulations
What are the main functions of CSF?
Hydraulic buffer to cushion brain against trauma
vehicle for removal of metabolites form CNS
Stable ionic environment for neuronal function (communicates with brain interstitial fluid via pia)
Transport of neurotransmitters and chemicals
What colour is normal CSF?
Normally clear sterile fluid
What colour is CSF in disease?
Discoloured in pathological states
Yellow (xanthochromia) - subarachnoid haemorrhage - lysis of red cells and haemoglobin release (converted to bilirubin)
Cloudy - Multiple sclerosis - protein content (gamma globulin) increase or in bacterial meningitis - leukocytes are increased, indicative of infection
How is CSF sampled?
Taken by lumbar puncture at lumbar cistern - No spinal cord L3/4 in adults or L3/5 in children
What is hydrocephalus?
Dilation of brain ventricles due to blocked CSF circulation, impaired absorption or over secretion
Increased intracranial pressure
Pressure on surrounding tissues affects neurological function
Can be congenital or acquired
What are the symptoms of hydrocephalus?
Headache, vomiting, visual disturbances, papilledema, seizures, altered cognition, balance and coordination problems
What is non communicating hydrocephalus?
Blockage within the ventricular system due to tumour, cyst, stenosis
CSF does not circulate over surface of the brain
Surgery: Inset shunt to reduce intracranial pressure
What is dandy walker syndrome?
Congenital malformation of the cerebellum
Obstruction in the 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 the arachnoid villi. Movement of CSF into venous sinus impaired
Eg. Impaired absorption following subarachnoid haemorrhage, trauma or bacterial meningitis
