A clear fluid called cerebrospinal fluid (CSF) is found in the cavities of the CNS. CSF is found in the ventricles of the brain (para 11 -9d), the subarachnoid space (para 11-11b(2)), and the central canal of the spinal cord (para 11 -10b(1)). CSF and its associated structures make up the circulatory system for the CNS.
a. Choroid Plexuses. Choroid plexuses are special collections of arterial capillaries found in the roofs of the third and fourth ventricles of the brain. The choroid plexuses continuously produce CSF from the plasma of the blood.
b. Path of the CSF Flow. Blood flows through the arterial capillaries of the choroid plexuses. As CSF is produced by the choroid plexuses, it flows into all four ventricles. CSF from the lateral ventricles flows into the third ventricle and then through the cerebral aqueduct into the fourth ventricle. By passing through three small holes in the roof of the fourth ventricle, CSF enters the subarachnoid space. From the subarachnoid space, the CSF is transported through the arachnoid villi (granulations) into the venous sinuses. Thus, the CSF is formed from arterial blood and returned to the venous blood.
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