MENINGES AND CSF

MENINGES AND CSF

Meninx is the protective covering of the CNS. It is composed of 3 layers:

• Dura mater
  • Parietal layer: covers the brain and the spine
  • Falx cerebri: folds over the midline of the brain
  • Falx cerebelli: folds over the cerebellum
• Arachnoid mater
  • Lies between dura and pia mater
  • Arachnoid villi: project into the venous sinuses to absorb CSF
• Pia mater
  • Lies next to the brain and spinal cord
  • Adheres to the surface of the brain and spinal cord

Cisterns are the sac-like spaces between the meninges, filled with CSF. They are located in the following places:

• Cisterna magna: between cerebellum and medulla oblongata
• Cisterna pontis: between pons and medulla oblongata
• Cisterna ambiens: between cerebrum and cerebellum

Ventricle is a fluid-filled cavity within the brain. There are 4 ventricles:

• Lateral ventricles: 2 ventricles located in the cerebral hemispheres
• Third ventricle: located between the 2 hemispheres
• Fourth ventricle: located between the cerebellum and medulla oblongata

Formation of CSF: CSF is produced by the choroid plexus in the ventricles. It is formed by the filtration of blood in the capillaries of the choroid plexus.

Circulation of CSF: CSF circulates through the ventricles and subarachnoid space. It is absorbed through the arachnoid villi into the venous sinuses.

Functions of CSF:

• Buoyancy of the brain
• Protection against trauma and infection
• Regulation of ion and fluid balance
• Transportation of nutrients and waste products

Applied Anatomy: CSF is produced at the rate of 500ml per day. It takes 4-6 hours to circulate through the ventricles and subarachnoid space. CSF is absorbed into the venous sinuses and is reabsorbed into the blood.

In a normal individual the CSF pressure should be around 50-200 mmH2O. In case of increased intracranial pressure the CSF pressure increases.

In case of blockage of CSF pathway, the CSF pressure increases and the ventricles become distended → hydrocephalus.