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Level 3 Level 3
Invertebrates Invertebrates

How Fast Are Neurons?

Have you ever wondered how fast signals travel in your nervous system? In this experiment, you’ll explore conduction velocity—the speed at which spikes travel down axons—using an earthworm as your model organism.

Neuron Speed Illustration

What Will You Learn?

  • How to measure the speed of neural signals (conduction velocity).
  • How to set up a dual-channel recording system for axons.
  • How conduction velocity varies between organisms and conditions.

Background

The nervous system is fast, but not instantaneous. But how fast can neurons send spikes? Faster than a bike? A car? a plane? To measure speed, we need to track both the time a spike takes and the distance it travels.

Procedure

In this experiment, we’ll use earthworms, which have long bodies and just three large axons—perfect for measuring conduction velocity. By recording spikes with two electrodes at different points along the worm, we can calculate how quickly signals are traveling.

Procedure

Ice does not work to anesthetize an earthworm. So you need to use alcohol. Grab a healthy night crawler and place it in a glass with 10% ethanol solution for 3–4 minutes.

Do not. keep the worm in for too long. Unlike the ice water, the alcohol can kill the earthworm if left in for too long.

Place the earthworm on your recording base: balsa wood, cork, or styrofoam will work. You will insert the three pin electrodes from your SpikerBox along the centerline of the worm. Spread out the two recording pins to have roughly the same distance between them, and arrange them so they are channel 1, channel 2, then the ground pin. Measure the distance between Pin 1 and Pin 2 (it about 2.6cm in the illustrations below.

 Use a plastic probe (like a coffee stirrer) to tap the posterior (back) end of the worm. This should illicit a single spike that travels down the center axon of the earthworm. You should be able to see the same spike on both channels.

Results & Analysis

Examine your recordings: spikes will appear first on channel 1 and later on channel 2. Measure the time difference between the spikes on both channels and calculate the conduction velocity using the formula:

Speed = Distance / Time

What did you observe? Does the speed vary between taps? Between worms? Record your findings and compare results across trials!