Production and circulation of cerebrospinal fluid with respect to the subarachnoid space of the optic nerve.

The function of cerebrospinal fluid (CSF) is to protect the brain and optic nerve from mechanical damage, provide nutrition for axons/neurons, and remove of toxic metabilites. CSF is produced mainly by the choroid plexus epithelium and ependymal cells of the ventricles and flows into interconnecting chambers; namely, the cisterns and the subarachnoid spaces. Based on studies of CSF circulation and direction of flow using radioisotopes and other tracers injected into the CSF, it is thought that there is a bulk circulation of fluid from the sites of production in the third, fourth, and lateral ventricles to the arachnoid villi and probably to the lymphatic capillaries in the cranial dura mater. The mechanism by which CSF is propelled is incompletely understood, but probably is influenced by the release of newly produced CSF, ventricular pulsations, and the pulse pressure of the vascular choroid plexus. This mechanism would account for the steady CSF pressure. In addition to the steady CSF pressure, overlapping pressure spikes occur during trunk inclination, coughing and other valsalva.