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| Question | Answer |
| Role of CSF | provides mechanical cushioning of brain |
| Where is CSF | subarachnoid space + around brain and spinal cord |
| Composition of CSF | Sodium (more than in plasma) Potassium (less than in plasma) Chloride (more than in plasma) Glucose (c.70% of plasma levels) Protein (v little) pH (7.3 - blood = 7.4) |
| Characteristics of normal CSF | clear, colourless few WBCs no RBCs v. little protein glucose |
| Total vol of CSF in subarachnoid space in ventricles | 140ml 117ml 23ml |
| why do blood and csf have different compositions | transporters promote entry of some substances while restricting entry of others from blood |
| normal pressure of csf | 10mmHg |
| flow of csf | lateral ventricles -> foramen of Monroe -> 3rd ventricle -> aqueduct of sylvius -> 4th ventricle -> foramen of magendie + foramina of luschka |
| Formation of CSF | In choroid plexus by ependymal cells |
| No. of choroid plexuses + structure | 4 2 cells thick - endothelial + ependyma connected by tight junctions = seals off capillary wall |
| Role of Blood-CSF barrier | restricts free movement of substances from blood -> CSF |
| Permeability to hydrophilic/lipophobic | low permeability transport tightly regulated - depends on presence of specific transporters in walls of ependyma |
| Permeability to lipophilic/hydrophobic | free unrestricted movement |
| Formation of Brain Interstitial Ffuid (ISF) | Formed by plasma at cerebral capillary wall Drains into CSF via subarachnoid space |
| Formation of blood brain barrier | formed by walls of cerebral capillaries + transporters + astrocytes |
| Structure of BBB | Single layer of flattened endothelial cells connected by tight junctions Surrounded by basement membrane + astrocytes |
| Role of BBB | Restricts movement of substances from blood -> brain ISF |
| Neurooncology of BBB | BBB absent in blood vessels associated with tumours = can use drugs that can't cross BBB to target these |
| Pressure of ICP | 10mmHg |
| Dangers of increased ICP | cerebral vessels compressed = - cerebral blood flow = cerebral ischaemia |
| Symptoms of + ICP | Initial = headache, restlessness Worsens = neural dysfunction (confusion, drowsiness) + Papilloedema If continued = Cushing's reflex |
| Cushing's reflex | occurs when considerable loss of cerebral perfusion = brain is severely hypocapnic + hypoxic |
| Hypercapnia | stimulates vasormotor sensor in medulla = peripheral vasoconstriction + arterial BP improve cerebral perfusion + firing in baroreceptors + activity of cardio-inhibitory centre Reflex bradycardia |
| Causes of + ICP | Brain haemorrhage Brain tumour Head injury/trauma |
| Contrecoup injury | when brain is driven against skull following a severe blow to opposite side of skull |
| Depressed skull fracture | when skull is fractured and bone is driven into brain tissue |
| Hydrocephalus | + CSF volume due to obstruction of CSF flow = enlargement of ventricles = brain flattened against skull = brain damage |
| People affected by hydrocephalus | Infants - stenosis/inflammation of aqueduct of sylvius Adults - obstruction of Aqueduct of sylvius (obstruction of 4th ventricle outflow) |
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