What fluid surrounds the brain and spinal cord?

The fluid that surrounds the brain and spinal cord is cerebrospinal fluid, commonly abbreviated CSF. It is a clear, colorless fluid that circulates through the brain’s ventricles and the subarachnoid space around the brain and spinal cord.

CSF provides buoyancy and acts as a protective cushion, reducing the effective weight of the brain and helping absorb shocks inside the skull. It also helps maintain the chemical environment of nervous tissue, transport certain substances, and remove waste through drainage pathways.

Most CSF is produced by the choroid plexuses inside the brain’s ventricles. It flows through connected cavities, exits into the subarachnoid space, and is eventually reabsorbed into venous circulation through arachnoid granulations and related drainage routes.

Ancient physicians, including Hippocrates, described fluid around the brain, but modern understanding developed much later. A lumbar puncture, often called a spinal tap, samples CSF near the lower spine to help investigate infections, bleeding, inflammation, and pressure abnormalities. CSF is not the same as plasma, lymph, or synovial fluid.