The human brain is composed of approximately 75% water. This water content is fundamental to its ability to perform all functions, from processing thoughts and memories to controlling physical movements. Maintaining the right balance of fluid within the brain is important for its operation and neurological health.
The Fluids Inside Your Skull
The “water” within the brain exists in different forms. A portion is found within the brain cells themselves, known as intracellular fluid, contained within neurons and glial cells, where it participates in cellular processes. Beyond the cells, the brain is surrounded and permeated by two other fluid types: cerebrospinal fluid (CSF) and interstitial fluid (ISF).
Cerebrospinal fluid is a clear liquid that acts as a cushion around the brain and spinal cord. It fills the spaces within the brain’s ventricles and the subarachnoid space surrounding the brain’s surface. The brain floats within this bath of CSF, which reduces its weight and prevents it from being crushed by its own mass.
Interstitial fluid occupies the spaces between the brain cells. This fluid environment is where neurons exchange nutrients, waste products, and chemical signals. While CSF is a more macroscopic fluid surrounding the brain, ISF is the fluid medium directly interacting with individual brain cells.
The Critical Roles of Brain Fluid
These fluids support neurological function. Cerebrospinal fluid provides buoyancy, allowing the brain to float and reducing its weight from about 1,400 grams to 50 grams. This buoyancy protects the brain by minimizing pressure on its delicate structures and acting as a shock absorber against sudden movements or minor impacts.
Fluid circulation also plays a role in waste removal from the brain. During sleep, a system known as the glymphatic system becomes more active, using CSF and ISF to flush out metabolic waste products. This system clears harmful substances, including proteins associated with neurodegenerative conditions, maintaining a healthy brain environment.
These fluids also serve as a transport system within the brain. They facilitate the delivery of nutrients, hormones, and other chemical messengers to brain regions. This constant circulation ensures that brain cells receive compounds for their metabolic activities and that communication pathways remain efficient.
When Fluid Builds Up
An imbalance where too much fluid accumulates in the brain can lead to a medical condition known as hydrocephalus. Often referred to colloquially as “water on the brain,” hydrocephalus involves a buildup of cerebrospinal fluid within the brain’s ventricles. This accumulation can occur due to a blockage in the CSF’s flow pathways, an overproduction of the fluid, or problems with its absorption back into the bloodstream.
As CSF accumulates, it exerts pressure on the surrounding brain tissue, damaging neural structures. This condition can affect individuals of all ages, from infants born with congenital forms to adults who develop it due to injury, infection, or other medical issues. The increased pressure can lead to a range of symptoms, and medical intervention is required to manage the fluid buildup and pressure on the brain.
The Effects of Dehydration on the Brain
Just as too much fluid can be problematic, dehydration also negatively impacts the brain. Even mild dehydration can cause brain tissue to shrink slightly, leading to cognitive effects. This shrinkage can disrupt normal brain function and contribute to uncomfortable symptoms.
Common signs of dehydration affecting the brain include headaches, a feeling of “brain fog,” and difficulty concentrating on tasks. People may also experience reduced alertness and changes in mood, such as irritability or fatigue. These symptoms underscore the importance of hydration for cognitive performance and general well-being.