CEREBROSPINAL FLUID

(CSF) clear, colourless liquid that fills the ventricles (cavities) of the brain and the spinal cord, surrounds them as well, and acts as a lubricant and a mechanical barrier against shock. The nervous system of the vertebrate embryo consists of a hollow tube with a canal running through its whole length. As the organism develops, the canal becomes narrow in the spinal cord, while widening in the brain and creating the ventricles. CSF is formed primarily in the ventricles, which serve as a network of interconnected holds. The fluid flows down through the brain-stem canal, and leaves the central nervous system by being absorbed into surrounding tissue spaces. CSF has a slightly alkaline chemical composition, similar to blood. It contains no red blood cells, though, and low amounts of protein and lipids in comparison to blood. It is about 99 percent water and freezes at 0.57 C (33 F). There are about 100 to 150 millilitres of cerebrospinal fluid in the normal adult body. The cerebrospinal fluid serves a mostly mechanical function. It bathes the brain and the spinal cord and helps support the brain's weight. It also provides lubrication for the surfaces created between surrounding bones and the brain and spinal cord. When an individual is hit on the head, the fluid acts as a buffer, dulling the blow by distributing its impact. The fluid helps keep pressure within the cranium at a constant level. An increase in the volume of blood or brain tissue results in a corresponding decrease in the fluid. Conversely, if there is a decrease in the volume of matter within the cranium, as occurs in atrophy of the brain, the cerebrospinal fluid compensates with an increase in volume. The fluid also transmits metabolic waste products, antibodies, abnormal chemical substances, and pathological products of disease away from the brain and spinal-cord tissue into the bloodstream. It also carries certain drugs to nervous-system tissue. The exact method of the formation of the cerebrospinal fluid is uncertain. It is believed that, after originating in the ventricles, it is filtered through the nervous-system membranes (ependyma). The formation of the fluid is a continual process, and all of it is replaced every six to eight hours, or three or four times a day. The fluid is eventually absorbed into the veins. It leaves the cerebrospinal spaces in a variety of locations, including spaces around the spinal roots and the cranial nerves. Some of it may be directly absorbed by veins on the brain surface. No specific organ propels the circulation of the fluid. Movement of the fluid is affected by the downward pull of gravity, the continual process of secretion and absorption, blood pulsations in contingent tissue, respiration, pressure from the veins, and head and body movements. Doctors use the cerebrospinal fluid to diagnose a number of body malfunctions and diseases. They gather the fluid by inserting a needle in the lumbar region of the lower back. Various diseases are indicated by a chemical analysis of the fluid, as well as by its appearance. If the fluid, which is clear and colourless in its normal state, is cloudy or opalescent, some form of meningitis (inflammation of the central nervous system lining) is indicated. Blood in the fluid indicates a hemorrhage in the ventricles or the brain.