CNS Module

CSF is a clear, colorless fluid that surrounds the brain and spinal cord, providing protection and support. Approximately 70% of CSF is produced by the choroid plexuses, which are specialized structures located within the ventricles of the brain. The choroid plexuses are formed by folds of the pia mater, a delicate membrane that covers the brain and spinal cord, and are highly vascularized, containing fenestrated capillaries that allow for the filtration of blood plasma. The remaining 30% of CSF is produced through filtration from brain capillaries.

The CSF circulates through the ventricular system and the subarachnoid space, which surrounds the brain and spinal cord. The circulation pathway can be summarized as follows:

1. Lateral Ventricles: CSF is primarily produced in the lateral ventricles, the largest ventricles in the brain.

2. Interventricular Foramina (of Monro): From the lateral ventricles, CSF flows through the interventricular foramina into the third ventricle.

3. Third Ventricle: A small amount of CSF is produced in the third ventricle, which is located in the diencephalon, a region of the brain above the brainstem.

4. Cerebral Aqueduct (of Sylvius): CSF then flows through the cerebral aqueduct, a narrow channel in the midbrain, into the fourth ventricle.

5. Fourth Ventricle: A small amount of CSF is also produced in the fourth ventricle, which is located between the brainstem and the cerebellum.

6. Subarachnoid Space: From the fourth ventricle, the majority of CSF flows through three openings – the foramen of Magendie (a single median opening) and the foramina of Luschka (two lateral openings) – into the subarachnoid space.

• A small amount of CSF also flows downward into the central canal of the spinal cord.

7. Cranial Venous Sinuses: CSF is ultimately drained from the subarachnoid space into the cranial venous sinuses, primarily the superior sagittal sinus, through arachnoid villi (finger-like projections of the arachnoid membrane). These villi act as one-way valves, allowing CSF to flow into the venous system but preventing blood from flowing back into the subarachnoid space.

• Arachnoid granulations are formed by the coalescence of arachnoid villi and project into the superior sagittal sinus, providing a larger surface area for CSF drainage.