Myelin

Your brain doesn't finish building its myelin highways until you're around 25 years old, with the prefrontal cortex—responsible for decision-making and impulse control—being the last area completed. This explains why teenagers can be brilliant yet impulsive: they literally have incomplete neural wiring. The process is so energy-intensive that it consumes about 20% of your body's total caloric intake during peak development periods.

Myelin increases nerve signal speed by up to 100 times, transforming sluggish 2 mph transmissions into lightning-fast 200 mph bursts. Without it, simple reflexes like pulling your hand from a hot stove would take seconds instead of milliseconds. Evolution essentially invented biological broadband 500 million years ago, giving vertebrates a massive competitive advantage over their slower-processing invertebrate cousins.

In multiple sclerosis, your immune system mistakes myelin for an invader and systematically destroys it, creating communication breakdowns throughout the nervous system. What makes this particularly cruel is that myelin repair becomes increasingly difficult with age—the same oligodendrocytes that built your neural superhighways in youth struggle to rebuild them decades later. It's like having construction crews that forget how to fix the roads they once built perfectly.

The white appearance of myelin-rich brain regions isn't just cosmetic—it represents nearly half your brain's volume and contains more neural connections than gray matter. Recent research reveals that white matter continues adapting throughout life, changing dramatically when you learn new skills like playing piano or speaking a language. Einstein's brain actually had unusually thick myelin in areas associated with mathematical processing.

Individual oligodendrocytes in your brain can extend up to 40 tentacle-like processes, each wrapping around different nerve fibers like biological gift-wrappers working multiple assembly lines simultaneously. A single oligodendrocyte can myelinate dozens of axons, while in the peripheral nervous system, each Schwann cell devotedly wraps just one nerve fiber. It's the difference between a multitasking octopus and a dedicated one-on-one personal trainer.

Your brain produces new myelin most actively during deep sleep, particularly during childhood and adolescence when neural development peaks. Sleep deprivation during critical developmental periods can permanently impair myelination, potentially affecting cognitive function for life. This reveals why teenagers naturally stay up late and sleep in—their brains are literally rewiring themselves during those extended sleep cycles, building the neural infrastructure they'll use as adults.