Why must glial cells support neurons? Neurons are specialized cells that receive and send signals to other cells through fragile and thin cellular extensions called axons. These axons extend over distances long and short to reach their target, ultimately connecting neurons with other nerve tissue, muscle tissue, or sensory organs (Figure 1A). For example, some motor neurons in the spinal cord have axons that exceed 1 m in length, connecting the spine to the lower limb muscles. These axons transmit signals to the target muscle in the form of electric impulses called action potentials. However, the axons alone are not enough to produce rapid conduction of the electric current necessary for this signal to be sent. Glial cells are the key element for supporting the messages neurons send and receive all over the body. Much like the insulation around the wires in electrical systems, glial cells form a membraneous sheath surrounding axons called myelin, thereby insulating the axon. This myelination, as it is called, can greatly increase the speed of signals transmitted between neurons (known as action potentials). Indeed, the evolution of myelin allowed vertebrates to achieve efficient nervous systems despite their large body…