T1 L12 Ventricular system & circulation of CSF Flashcards
What is the ventricular system?
Series of CSF-filled interconnected spaces
Continuous with subarachnoid space & central canal
What forms the neural tube?
Neuroectoderm
What forms the ventricles & central canal?
Lumen of the neural tube
What does the ependymal layer line?
The ventricles & central canal
What does the telencephalon form?
Cerebral hemispheres
What does the diencephalon form?
Thalamus / hypothalamus
What does the mesencephalon form?
Midbrain
What does the metencephalon form?
Pons / cerebellum
What does the myelencephalon form?
Medulla
Where does the anterior horn sit?
In the frontal lobe
What does the inferior horn sit?
Temporal lobe
Where does the posterior horn sit?
Occipital lobe
What separates the lateral ventricles?
Septum pellucidum
Where does the corpus callosum sit?
In the roof of the lateral ventricles
What are the lateral ventricle borders?
Caudate nucleus sits in lateral wall
Hippocampus sits in floor of inferior horn
What is the function of the interventricular foramen?
Way for the lateral ventricles to communicate with the third ventricle
Also called Foramen of Monro
What forms the roof of the third ventricle?
The fornix
Where is the third ventricle?
Sits like cleft between thalami
What is the cerebral aqueduct?
Way for the third ventricles to communicate with the fourth ventricle
Also called aqueduct of Sylvius
What surrounds the cerebral aqueduct?
Surrounded by the midbrain
What is the fourth ventricle surrounded by?
Hindbrain
Posterior - cerebellum
Anterior - pons & medulla
Lateral - cerebellar peduncles
Describe the fourth ventricle communication
3 foramen exit into subarachnoid space:
2 foramen of Luschka (lateral)
1 foramen of Magendie (middle)
Into cisterns magna
What is the function of the choroid plexus?
Produces CSF
Filters blood from branches of internal carotid & basilar arteries
Present throughout ventricles
What is the structure of the choroid plexus?
Very simple
Capillary network surrounded by cuboidal epithelium
What happens during CSF production?
1) Blood filtered through fenestrated capillaries
2) Components transported through cuboidal epithelium into ventricles
What are the functions of the tight junctions between the epithelial cells in the choroid plexus?
Prevent macromolecules from entering CSF
Permeable to water & CO2
Forms blood-CSF barrier
Describe cuboidal epithelium
Specialised ependyma
Villi present to increase surface area
Active transport of CSF components
Bidirectional - uptake of metabolites into circulatory system
What is the composition of CSF?
Differs in ionic composition compared to plasma
Protein is much lower at 0.18
Differences due to regulation by active transport
Very few cells
Ideal for physiological functioning of neurons
Describe the flow of CSF
Lateral ventricles –> inter ventricular foramen –> third ventricle –> cerebral aqueduct –> forth ventricle –> Luschka & Magendie foramina –> cisterns magna –> out ventricles into subarachnoid space
Where is the subarachnoid space?
Between the Pia & arachnoid
Follows contours of brain
What is the functional importance of the subarachnoid space?
CSF in contact with brain parenchyma to allow transfer of micronutrients into the brain & removal of metabolites
What are arachnoid granulations?
Herniations of arachnoid membrane through dura mater into venous sinuses
Mainly within superior sagittal & transverse sinuses
Describe the absorption of CSF
CSF pressure must exceed that in venous sinuses (150mm in subarachnoid, 80mm water in venous sinuses)
If venous pressure exceeds CSF pressure the tips of villi close off to prevent reflux of blood into subarachnoid space
What is the volume of CSF?
500ml produced per day
90-140ml in system
Continuously moving
Excess absorbed by arachnoid granulations
What are the main functions of CSF?
Hydraulic buffer to cushion brain against trauma
Vehicle for removal of metabolites from CNS
Stable ionic environment for neuronal function
Transport of neurotransmitters & chemicals
What can make CSF yellow?
(Xanthocromia)
Subarachnoid haemorrhage - lysis of RBC, haemoglobin release
What can make CSF cloudy?
Multiple sclerosis - protein content increase
Bacterial meningitis - leucocytes are increased
How do you sample CSF?
Lumbar puncture
At lumbar cistern as there is no spinal cord here
L3/L4 in adults
L4/L5 in children
What is hydrocephalus?
Dilation of brain ventricles
Increased intracranial pressure
Congenital or acquired
What can cause hydrocephalus?
Blocked CSF circulation
Impaired absorption
Over secretion
What are the symptoms of hydrocephalus?
Causes pressure on surrounding tissues which affects neurological function Headaches Vomiting Visual disturbance Papilledema Seizures Altered cognition Balance & coordination problems
What is non-communicating hydrocephalus?
Blockage within ventricular system
CSF doesn’t circulate over surface of brain
What can cause a blockage in the ventricular system?
Tumour
Cyst
Stenosis
What surgery is done for non-communicating hydrocephalus?
Insert shunt to reduce intracranial pressure
What is Dandy-Walker syndrome?
Congenital malformation of cerebellum
Obstruction within foramina of fourth ventricle - symmetrical dilation of lateral, third & fourth ventricles
In infancy the child’s head may become enlarged
What is communicating hydrocephalus?
Obstruction in arachnoid villi
Movement of CSF into venous sinuses is impeded
What are some causes of communicating hydrocephalus?
Impaired absorption following subarachnoid haemorrhage
Trauma
Bacterial meningitis
