A Neural Butterfly

What am I looking at?

This is a stained cross section through a human spinal cord under darkfield illumination. The darker portion toward the middle is gray matter – central nervous system cell bodies and unmyelinated axons (1); myelin is a fatty coating on some but not all axons. The lighter portion around the exterior is white matter – mainly fibers covered in myelin that send signals to and receive signals from the peripheral nervous system (2). The hole in the very middle is the central canal containing cerebrospinal fluid (3).

Biology in the background

The spinal cord connects the brain to the rest of the body. It is housed within the spine, which protects the cord’s cells and fibers. The spinal cord relays signals from the brain to the rest of the body and from the body back to the brain.

However, the spinal cord is not just a relay station. Some neuronal information is processed within the spinal cord itself. For example, reflex actions – such as the way the body responds to touching a hot stove or being tapped on the patellar tendon in the knee – are so fast because they don’t need to be communicated to and from the brain. When sensory neurons detect stimuli that cause a reflex reaction, they send signals to interneurons in the spine. The interneurons then pass the signals directly to motor neurons that carry out the reflex – such as pulling your hand away from the hot stove or jerking your foot.

A human spinal cord is about 13 millimeters across, or slightly smaller than a human thumbnail.

Technique

This image was created using a form of light microscopy called darkfield illumination.