Myelin Your Manners

What am I looking at?

This is an electron microscopy image of the severed end of a nerve in the spinal root of a rat. You can see the myelin sheaths (1) around the circumference of each of the axons in the nerve. The interior of the axons, called axoplasm (2), can be seen in the middle of each axon.

Biology in the background

An axon is the part of a neuron that sends a signal to other cells. Axons extend from the cell body to contact other cells, generally forming synapses between the two cells. These axons can be very long. In fact, in humans, there is a neuron that originates at the bottom of your spine and sends an axon all the way down your leg to the tip of your toe. To send a signal this distance in a timely manner, neurons use electricity, which can travel much faster than chemical signals. The electrical impulses that neurons use are called action potentials. They are generated where the axon meets the cell body, they travel down the axon, and then they trigger the release of neurotransmitters at the synapse.

To make these electrical signals travel even faster, sections of the outer surface of many axons are coated with a layer of lipids (fats) called myelin. Myelin acts as an electrical insulator, allowing the signal to hop between unmyelinated sections of the axon until it reaches the end.

Axons in the spine of a rat can vary in size but on average are around 1 micrometer across, or roughly 75 times smaller than the width of a human hair.

Technique  

This image was created using scanning electron microscopy.