A commonly-used term for subarachnoid channelsCerebrospinal fluid forms, for the most part, within the ventricles of the brain. From there it flows out, at the base of the brain, and on over the surface of the brain, then to be re- absorbed back into the bloodstream, mainly into the superior sagittal sinus. Some also flows into the spinal canal. The ventricles and other courses along which the cerebrospinal fluid flows, inside the head and the spinal canal, make up the subarachnoid channels. The term subarachnoid space is commonly used, arguably in error as it implies that these channels are empty, whereas they are, in life, “flooded” with cerebrospinal fluid., reflecting the fact that, in dissection room preparations, the volume between the duraThis is the outer, most prominent and the toughest of the three different membranes that invest the brain and spinal cord. It also forms the lining of the cranial cavity and the spinal canal. Looked at as a whole, the dura can be envisaged as a balloon with a long sausage skin hanging below it. Within the dura the brain and spinal cord are bathed in cerebrospinal fluid. and the brain or spinal cordThe main nerve trunk running down the spinal canal and connecting the individual’s mind and consciousness to the rest of his or her body. It is about the size of a person’s little finger, in diameter. It cannot repair itself if damaged. is empty. In life, this volume is filled with cerebrospinal fluidThis clear, water-like fluid forms, for the most part, within the brain, more specifically inside the ventricles of the brain. Blood flows through structures inside the ventricles, called the choroid plexuses, and clear fluid is produced as a result, passing into the ventricle. This process is akin to blood flowing through the kidneys and urine being produced as a result. An important difference is that, unlike urine, the cerebrospinal fluid is not passed out of the body periodically. Instead, the fluid is re-absorbed back into the blood stream, mostly via the arachnoid granulations, into the cerebral venous sinuses. In the course of a 24-hour period, most healthy adults will produce about 500mls (or a pint) of cerebrospinal fluid, although at....