New York University neuroscientist Charles Nicholson explains:
It’s now known that every cell in the brain is separated from its neighbor by a fluid-filled extracellular space (ECS), which forms sheets and tunnels, as shown on page 26 in a computer reconstruction of the ECS in a rat’s brain. That interstitial fluid is predominantly an aqueous solution of sodium chloride with small concentrations of many other essential substances, such as potassium, calcium, and several amino acids and peptides. The ECS also hosts a sparse extracellular matrix of larger molecules. The space between cells is exceedingly narrow—much of it only tens of nanometers wide—and thus one of the most difficult domains of the brain to study in the living state. But without the ECS, electrical signals wouldn’t pass between neurons, metabolic substances and chemical signals wouldn’t disseminate, and drugs wouldn’t reach their targets. The long journey to finally observe and understand the ECS was made possible by innovations in the analysis of molecular diffusion.Charles Nicholson, “The secret world in the gaps between brain cells” at Physics Today (May 26, 2022)
The paper is open access.
And it all just sorta happened. Didn’t that account work better when the brain was a grey mush?