CNS: Revision Flashcards
What are the neuroglia?
Non-neuronal and non excitable support cells
3 kinds of the macroglial cells?
Oligodendrocytes (wrap around axons and form myelin sheathes)
Astrocytes (metabolic buffers, detoxifiers, insulation, repair and scarring)
Empendymal cells (CSF production)
What are the microglia of the CNS?
Fixed macrophage system within the CNS
What is on outside of brain, grey or white matter?
Grey matter
Name the layers of the meninges
Dura mater Arachnoid mater Subarachnoid space Arachnoid mater Pia mater
Regulatory centres in the brainstem? (7)
Vomiting Swallowing Respiratory Urinary bladder control Pneumotaxic Cardiac acceleration Cardiac slowing
What produces CSF?
Choroid plexus of the lateral third and fourth ventricles
Where does CSF travel to
Exits ventricular system through the foramina of Luschka and Magendie, into the subarachnoid space.
From here, descends into spine or ascends to bath the brain
What drains the CSF?
Superior sagittal sinus
Normal volume of CSF?
120ml, changed 3-5 times a day
What is the most common form of acute hydrocephalus?
Obstructive hydrocephalus, where there is obstruction to flow of CSF
What may cause obstructive hydrocephalus? (4)
Previous meningitis
Tumours of the posterior fossa or the brainstem (blocks the fourth ventricle)
Tumours of the third ventricle eg colloid cysts, are a well known cause and can lead to sudden death
Congenital causes eg CHirari malformation
What is a Chiari malformation?
Defect in the posterior fossa or cerebellum causes blockage of CSF flow at the foramen magnum
What is hydrocephalus ex Vacuo?
A COMPENSATORY increase in CSF seen in certain dementia. There is ventricular enlargement due to loss of brain parenchyma.
Gross changes to the brain with hydrocephaly?
Dilation of the ventricles
Corresponding decrease in white matter
Normal intracranial contents attributing to pressure?
Brain- 70%
CSF 15%
Blood 15 %
Causes of raised ICP (4)
Mass effect:
- Tumours
- Abscess
- Infarction
- Haemorrhage
Clinical features of raised ICP (8)
Dizziness
Headache
Vomiting
Confusion
Focal neurological signs (paralysis, hemianopia, dysphasia)
Papilloedema
Seizure
Decreased consciousness
Four stages of raised ICP
- SPATIAL COMPENSATION by reduction in blood flow or brain
- ICP rises as COMPENSATION IS EXHAUSTED: Systemic arterial pressure may correspondingly increase
- ICP rises rapidly as cerebral perfusion decreases
- CEREBRAL VASOMOTOR PARALYSIS where ICP=SAP and cuts off blood supply
What is the 4th stage of rasied ICP?
Cerebral vasomotor paralysis as ICP=SAP and cuts off blood supply
If the lesion causes ICP to raise at a high rate, how does this affect mortality compared to slower rate?
No set pressure where death occurs
Higher rate will exhaust compensatory mechanisms quicker
How does a raised ICP affect the brain grossly? (4)
Flattening of gyral pattern
Compression of ventricle on same side as lesion
Lateral shift of midline structures if the lesion is unilateral
Internal hernation
What is a subfalcine herniation?
When cingulate gyrus herniates under Falx Cerebri
What is an uncal hernation? What nerve is compressed?
Brain herniates through the tentorial incisura
Compresses CNIII
Posterior artery compression
Haemorrhage in midbrain and pons
What artery is compressed in uncal herniation?
Posterior cerbral
What is a tonsillar herniation?
Cerebellar tonsils herniate down the foramen magnum leading to brainstem compression
What is vasogenic oedema?
A type of cerebral oedema where the integrity of the normal BBB is disrupted.
Can be local (eg due to abcess, tumour, infarct) or generalised (sepsis)
What is cytotoxic oedema?
A type of cerebral oedema where the is an increase in INTRACELLULAR fluid secondary to hypoxia or ischaemia
What is interstitial oedema?
A type of cerebral oedema that is due to increased water content within the peri-ventricular tissues
Occurs in acute hydrocephalus
Treatment for cerebral oedema
Steroids for inflammation or tumour
Surgery for haemorrhage
