Select the best answer or answers from the choices given: Cerebrospinal fluid is formed by (a) arachnoid granulations, (b) dura mater, (c) choroid plexuses, (d) all of these.
The Correct Answer and Explanation is :
The correct answer is: (c) choroid plexuses.
Explanation:
Cerebrospinal fluid (CSF) is a clear, colorless liquid that surrounds and cushions the brain and spinal cord, providing both mechanical protection and a stable environment for neuronal activity. The production of CSF is primarily carried out by the choroid plexuses located within the ventricles of the brain.
Formation of CSF:
- Choroid Plexuses: The choroid plexuses are specialized structures in the walls of the brain’s ventricles (primarily the lateral, third, and fourth ventricles). They consist of a network of capillaries enveloped by ependymal cells. These ependymal cells play a critical role in selectively filtering blood plasma to produce CSF.
- Mechanism: The process involves filtration, secretion, and active transport mechanisms. Blood plasma passes through the capillaries of the choroid plexuses, and the ependymal cells modify the composition to form CSF, ensuring it is free of large proteins and other blood components.
Why not the other options?
- Arachnoid Granulations (a): These structures are involved in the reabsorption of CSF into the venous system, not its formation. They are projections of the arachnoid mater into the dural venous sinuses, where they act as one-way valves to allow CSF to drain into the bloodstream.
- Dura Mater (b): The dura mater is one of the three meningeal layers protecting the brain and spinal cord. It does not play a role in the formation of CSF; its role is structural protection and support.
- All of these (d): This is incorrect because only the choroid plexuses are responsible for CSF formation.
Thus, (c) choroid plexuses is the best answer. The CSF formed circulates through the ventricles and subarachnoid space before being reabsorbed by arachnoid granulations, maintaining a dynamic balance.