Your brain is home to an extraordinary network of nerve fibres that allows different regions of the nervous system to communicate. Many of these fibres are wrapped in a fatty substance called myelin, which acts like insulation and helps electrical signals travel rapidly along nerve cells.
Some popular estimates place the combined length of myelinated nerve fibres in a young adult brain at around 160,000 kilometres. That is roughly four times the circumference of Earth. The exact total depends on how nerve fibres are measured and which structures are included, so the figure should be treated as an estimate rather than a universal measurement.
This microscopic communication network helps your brain coordinate movement, process sensory information, form memories and support thought. Myelin is especially important because it allows signals to travel efficiently, helping different parts of the brain and body work together.
When myelin is damaged, nerve signalling can become disrupted. Conditions such as multiple sclerosis demonstrate just how important healthy myelin is for normal nervous system function.