The ventricular system Flashcards
Development of ventricles
Neuroectoderm froms neural tube
Lumen of neural tube becomes ventricles and central canal
Ependymal layer lines ventricles and central canal
Lumen expands at cranial end to form ventricles
There is a ventricle associated with each part of the brain
Lateral ventricles
Two ventricles- very large
One for each cerebral hemisphere
Body, anterior, posterior and inferior horn corresponding to lobes of the hemisphere
Surrounded by telencephalon
Lateral ventricle borders
Septum pellucidum separates lateral ventricles
Corpus callosum sits in roof
Caudate nucleus sits in lateral wall
Hippocampus sits in floor of inferior horn
Interventricular foramen
Lateral ventrciles communicate with the thrd ventricle through the interventricular foramen
Also called foramen of monro
Third ventricle
Slit like cleft between thalami
Fornix forms roof
Cerebral aqueduct
Third ventricle communicates with fourth ventricle through cerebral aqueduct
Also called aqueduct of sylvius
Surrounded by midbrain
Fourth ventricle
Surrounded by hind brain
- cerebellum posterior
- pons and medulla anterior
- cerebellar peduncles lateral
Characteristic rhomboid shape
Continuous with the central canal of the spinal cord and subarachnoid space
Fourth ventricle communication
Three foramen exit into subarachnoid space:
- two foramen of luschka
- one foramen of magendie
Choroid plexus
CSF produced by choroid plexus
Filters blood from branches of internal carotid and basilar arteries
Choroid plexus present throughout ventricles
Structure of the choroid plexus
Very simple
Capillary network surrounded by cuboidal epithelium
During CSF production:
- Blood filtered through fenestrated capillaries
- Components transported through cuboidal epithelium into ventricles
Tight junctions between epithelial cells
Tight junctions between epithelial cells in choroid plexus
Prevent macromolecules from entering CSF
Permeable to water and CO2
Cuboidal epithelium
Specialised ependyma
Villi present to increase surface area
Active transport of CSF components
Bidirectional
CSF composition
Differs in ionic composition compared to plasma
Differences due to regulation by active transport
Very few cells
Ideal for physiological functioning of neurones
CSF circulation
Lateral ventricles -> . (interventricular foramen)
Third ventricles -> (cerebral aqueduct)
Fourth ventricle -> (luschka and magendie foramina)
Cisterna magna (subarachnoid space)
Subarachnoid space
Lies between pia and arachnoid
Subarachnoid space follows contours of brain
Functionally important: CSF in contact with brain parenchyma
- transfer of micronutrients into brain
- removal of metabolites
Arachnoid granulations
Herniations of arachnoid membrane through dura mater into venous sinuses
Mainly within the superior sagittal and transverse sinuses
Absorption of CSF
CSF pressure must exceed that in venous sinuses
- 150mm water in subarachnoid space
- 80mm water in venous sinuses
If venous pressure exceeds CSF pressure
- tips of villi close off
CSF volume
500ml CSF produced per day
Total volume in system = 90-140ml
Continuously moving
Excess absorbed by arachnoid granulations
Main functions of CSF
Hydraulic buffer to cushion brain against trauma
Vehicle for removal of metabolites from CNS
Stable ionic environment for neuronal funciton
Transport of neurotransmitters and chemicals
Colour of CSF in disease
CSF normally clear sterile fluid
Discoloured in some pathological states
- yellow (xanthocromia): e.g. subarachnoid haemorrhage
- cloudy: e.g. multiple sclerosis, bacterial meningitis
CSF sampling
Taken by lumbar puncture
At lumbar cistern
- no spinal cord
Hydrocephalus
Dilation of brain ventricules
Due to blocked CSF circulation, impaired absorption or over secretion
Increased intracranial pressure
Pressure on surrounding tissues affect neurological function
Can be congenital or acquired
Non- communicating hydrocephalus
Blockage within the ventricular system
- due to cyst, tumour, stenosis
CSF does not circular over surface of brain
Insert shunt to reduct intracranial pressure
Dandy- Walker syndrome
Congenital malformation of the cerebellum
Obstruction within foramina of fourth ventricle
In infancy, child’s head may become enlarged
Communicating hydrocephalus
Obstruction in the arachnoid villi
Movement of CSF into venous sinuses is impeded
E.g. impaired absorption following subarachnoid haemorrhage, trauma or bacterial meningitis
