Cerebrospinal Fluid (CSF) PDF

CEREBROSPINAL FLUID MD224 Professor Karen Doyle Neurophysiology [email protected] Recommended reading: A-20 – A-31 in Neuroscience 6/e, Purves et al Cerebrospinal fluid Transcellular fluid Highly regulated Blood brain barrier Body fluid compartments Blood brain barrier Ma...

CEREBROSPINAL FLUID MD224 Professor Karen Doyle Neurophysiology [email protected] Recommended reading: A-20 – A-31 in Neuroscience 6/e, Purves et al Cerebrospinal fluid Transcellular fluid Highly regulated Blood brain barrier Body fluid compartments Blood brain barrier Macroglia Movement of substances across capillary membrane into brain • Passive diffusion – directly proportional to lipid solubility and inversely proportional to size • Facilitated diffusion • Active transport • Vesicular transfer • Transcytosis • Endocytosis and exocytosis • Paracellular aqueous transfer Abbott NJ et al. (2006) Astrocyte–endothelial interactions at the blood–brain barrier Nat. Rev. Neuro. 7: 41–53 doi:10.1038/nrn1824 • Endothelial cells of capillary • Endfeet of astrocytes induce tight junctions Cerebrospinal fluid • A‘sink’ of extracellular fluid filtered from blood that supplies and drains the interstitium • 140 - 150 ml • Ventricles (~25ml), spinal cord central canal (~30ml), sub-arachnoid space (majority of vol) • Systolic pulsations of arterial system cause compression of ventricles and subarachnoid space creating movement • Rate of production: 550 ml/ day (0.35ml/min) • Reabsorbed through arachnoid villi into veins via venous sinuses • Turns over 3.7 times/ day Blood vessel to Interstitial space transfer Choroid plexi Abbott NJ et al. (2006) Astrocyte–endothelial interactions at the blood–brain barrier Nat. Rev. Neuro. 7: 41–53 doi:10.1038/nrn1824 Cerebrospinal fluid • 50-70% produced by choroid plexi • Considerable proportion also produced by blood vessel to interstitial space transfer – facilitates rapid delivery of oxygen and nutrients to a local area Cerebrospinal Fluid as a buoyancy aid and a cushion • Buoyancy • • • • Brain weighs 1400g in air CSF fills subarachnoid space and acts as a float Effective weight of brain floating in CSF is 50g Permits attachments to support brain – Blood vessels, nerve roots, fine fibrous arachnoid trabeculae • Protective function • CSF in subarachnoid space also cushions against injury Intracranial pressure (ICP) • Within skull: Brain, blood, CSF • Direct ICP recording: icv, subarachnoid or subdural • CSF pressure is often a guide of ICP • 120-180 mmCSF or 9-14 mmHg • Lumbar puncture procedure • ICP can be significantly raised through obstruction of venous system, intracranial mass, brain oedema http://www.hopkinsmedicine.org/healthlibrary/test procedures/neurological/lumbar_puncture_lp_92,P07666/ Analysis of CSF • L3-4 interspace Pressure 120-180 mmCSF (9-14 mmHg) Colour clear RBCs none WBCs 0-6mm3 Protein 15-45 mg/100 ml Glucose 50-75 mg/100 ml Low: dehydration, blockage High: tumour, abscess, cyst, hydrocephalus Cloudy: ↑cell count, infection Yellow: RBCs Traumatic tap, subarachnoid haemorrhage Meningitis, parasitic infections, MS, neurosyphilis Many disorders Low: meningitis High: diabetes CSF composition • Composition of extracellular fluid in CNS is highly regulated by bbb • Circumventricular organs: exception – outside blood brain barrier – Sites of physiological and endocrine feedback systems within the brain – Rapid venous drainage from these sites, which allows maintenance of integrity of blood brain barrier