**2. Cerebrospinal fluid: dynamics and function**

Adult CSF volume is estimated to be 150 ml with a distribution of 125 ml within the subarachnoid spaces and 25 ml within the ventricles. This difference in the volume of CSF between the two compartments is important to understand the function of the CSF in a unique perspective.

The CSF secretion varies between individuals, usually ranging between 400 and 600 ml per day in an adult. The constant secretion of CSF contributes to a four to five times turnover per 24-h period. This turnover is of immense importance in exploring the functions of the CSF which have not yet been understood quite well. While the CSF has been considered as a source of nutrition and waste removal and a mechanically buoyant substance, cushioning the brain, the newer insights of the glymphatic pathways have demonstrated a critical role of CSF flow as a physiological buffer for brain functioning.

With a closely regulated composition, the CSF is valuable in analyzing cerebral pathologies. Alterations in the regulation of localized temperatures, malformation of proteins, and impeding clearance of pathologic proteins are the pathophysiological mechanisms for onset and progress of most neurodegenerative disorders as well as secondary brain damage in the setting of trauma. It is, however, interesting to analyze how the impairment of CSF inflow or outflow through the glymphatic system might lead to the cascade of these degenerative and traumatic pathologies.
