Meninges and CSF Dr. K. Sivapalan

Meninges Dura mater, arachnoid mater and pia mater. Dura- single and tough layer of fibrous tissue fused with inner periosteum except in few areas. Arachnoid- fibrocellular tissue. Outer most cells are bonded to each other by tight junctions. Subarachnoid space- arachnoid trabeculae cross the space to reach the pia. [CSF] Pia- invests the nervous tissue closely lining the outer surface. It and the sub-pial space follow into the tissue with blood vessols. Meningies and CSF

Choroid Plexuses Choroid plexus is found in the 4 ventricles. Meningies and CSF

CSF and ECF in Brain CSF volume is about 150 ml, production is 550 ml/day, 50-70 % secreted by choroid plexus and the rest by vessels in the walls of the ventricles. The composition is the same as the ECF in the brain which is 15 % of the brain volume. The pia is freely permiable to CSF and there is free communication and diffusion of substances between the CSF and the ECF. Meningies and CSF

Circulation of CSF CSF enters the third ventricle through the inter ventricular foramen. It descends to the fourth ventricle through the aqueduct. It enters the subarachnoid space through median and lateral apertures in the roof of the fourth ventricle. Flow in the central canal of the spinal cord is negligible Some CSF descends through foramen magnum reaching the lumbar cistern in 12 hours. Small amount is absorbed into the spinal veins but most returns to subarachnoid space in cranium. It ascends further through the tentorial notch and around the cerebrum. Finally it is absorbed into the venous sinuses. Meningies and CSF

Function of the CSF The weight of brain in air is 1400 g but in the “water bath” of CSF, it is 50 g. The brain is attached and held in position by arachnoid trabaculae, blood vessels and nerve roots. Weight reduction by CSF helps the flimsy attachments to hold the brain. Removal of CSF can cause sever pain because the brain hangs on the vessols. The brain is protected from the trauma of head injuries by the CSF and meninges. Meningies and CSF

Abnormalities of CSF When circulation is blocked CSF pressure increases proximal to the obstruction. Block of foramina in the fourth ventricle or failure of absorption results in hydrocephalus. Abnormalities in composition signifies the type of disease of the meninges. Entricle results in internal hydrocephalus Meningies and CSF