Cerebrospinal fluid plays an important role in cushioning and protecting the brain from major shocks. It also plays an important role in the homeostasis and metabolism of the central nervous system.
CSF Flow- CSF is produced from arterial blood by the choroid plexus of the lateral and fourth ventricles
- CSF flows through the inter ventricular foramina into the third ventricle.
- CSF flows down the cerebral aqueduct into fourth ventricle.
- CSF flows out two lateral apertures and one median aperture.
- CSF fills subarachnoid space and bathes external surface of brain and spinal cord.
- At the arachnoid villi (granulations), CSF is reabsorbed into the venous blood of dural venous sinuses.
- The arachnoid villi acts as a one-way valves between the subarachnoid space and dural sinuses.
- The rate of CSF reabsorption depends on CSF pressure.
Image taken from https://jcmanagement.co/cerebrospinal-fluid/
Blood-Brain Barrier (BBB) - The BBB consists of endothelial cells lining the brain capillaries.
- It serves to restrict and control the movement of substances between the general circulation and brain extracellular fluid.
- It helps regulate the volume and composition of fluid surrounding the brain, thus contributing to homeostasis of the CNS.
- This can be controlled hormonally, or by surrounding cells like astrocytes.
- The BBB Is able to act as a barrier due to:
- tight junctions that restrict movement of substances between endothelial cells
- specific transport proteins that determine which substances can cross the barrier
- In conditions where drugs need to be administered to treat neurological conditions, the drugs need to be designed to bypass the restrictive barrier.
- Pathological conditions associated with the central nervous system may alter BBB function.
The image below shows the difference between normal blood vessels and blood vessels in the brain. Image taken from https://ibleedrainbow.wordpress.com/2016/10/19/blood-brain-barrier-blood-csf-barrier/ |
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