Definition
The *myelin sheath* is a fatty insulating layer that surrounds the axons of many neurons. It's formed by specialized cells (Schwann cells or oligodendrocytes) that wrap around the nerve fiber. It's like the plastic coating around electrical wires 🛡️, preventing signal loss and speeding up transmission. The *myelin sheath* ensures efficient communication within the nervous system. Without it, neural signals would travel much slower.