 250 miles per hour. That's the speed of the fastest cars in the world. It's also the speed at which messages travel from our brain to the rest of the body, telling our legs to walk or our hand to grab a drink when we're thirsty. That's incredibly fast and it's necessary in order to allow us to interact with and respond to the world around us. These messages travel in the form of electricity down specific paths made up of long chains of cells called neurons. The neuron is a very unusual type of cell in the body because it has very long extensions. The neuron has a cell body which contains a nucleus, surrounded by cell membrane extensions or processes called dendrites, which act like antenna to receive signals from other neurons. The neuron then extends a single very long process called an axon that ends in the axon terminal. Some axons can be very long, one meter in case of some neurons in your leg. The electrical signal travels from the cell body down the axon to the terminal. The terminal is then triggered to release a chemical signal that travels from that neuron to another one. This starts an electrical current in that second neuron. And so electrical signals pass from one neuron to another to another, allowing a thought that starts in your brain to travel to a muscle in your foot. Since axons are the long distance wires in this communication circuit, fast transmission of the electrical signal down the axon is crucial for us to chase down a flyaway umbrella or jump out of the way of a falling rock. To enable this rapid transport of a message along the axon, our bodies rely on myelin. Although observed as part of the nervous system as early as 1717, myelin was first named as such by Rudolf Wirko, a German physician, writer, and politician in 1854. Scientists theorized a few years later that myelin was providing the axon with insulation, which, as in a wire, allowed the electrical signal to move fast, with minimal signal loss, as it traveled down the neuron. This idea proved to be correct. Now, we know much more about myelin. It is a fatty substance that covers the axon in long sections. The fatty myelin is actually long extensions of cell membranes made by supporting cells called glia that wrap around the axons in concentric circles. In the central nervous system, meaning the brain and spinal cord, the glial cells that wrap their membranes around axons are called oligodendrocytes. And in the peripheral nervous system, in the nerves that travel throughout the body, they are called Schwann cells. The myelin wrapping is separated by very short, unmyelinated gaps that were spotted by French physician Louis-Antoine Ranvier. They were then named after him as the nodes of Ranvier. The electrical signal jumps between these nodes, traveling down the neuron. Without the nodes, transport would be at least 15 times slower. Not enough for us vertebrate humans. However, some animals, such as the squid and octopus, have developed creative ways to enable fast message transport without using myelin. These creatures have axons with a much larger diameter, which reduces the resistance the signal experiences in a thinner axon, allowing the signal to still move quickly through the animal's body and allow them to escape from predators. In humans, if the nerve cells become demyelinated, the transmission of the electrical message can be slowed from the normal 250 miles per hour to 100 miles per hour. Multiple sclerosis, or MS, is a disease caused by loss of myelin. The oligodendrocytes that form the myelin are lost. In MS, message transport and delivery are slower in the spinal cord, brain, and eyes. Patients develop symptoms such as fatigue and trouble with vision, and in the long run can suffer brain damage. While there is no cure yet for multiple sclerosis, many scientists around the world are working to try and understand the underlying cause of MS and other disorders involving myelin. Treatments that preserve or replace the myelin-producing cells could transform the lives of the millions of people currently living with MS in the United States.