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Small Muscle Action Potentials
  • Human
  • Grade 9+

Recording Individual Motor-Unit Action Potentials in Small Muscles

Have you ever wondered how your fingers move so precisely when typing, texting, or playing an instrument? This experiment explores the hidden electrical signals behind these precise movements. Using a SpikerBox, you’ll see firsthand how subtle electrical changes control movement direction, strength, and dexterity—revealing the amazing connection between neurons and muscles.

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About the Experiment

What Will You Learn?

What Will You Learn?

  • How your brain finely tunes muscle force using firing rate and motor unit recruitment.
  • How to record EMG signals from small muscles (like those in your hand) using the Human SpikerBox.
  • How electrode placement reveals distinct patterns of muscle activation.
Background

Background

Muscles contract using two key strategies: increasing firing rate (how fast neurons fire) and recruiting more motor units (adding more muscle fibers). Everyday actions seamlessly blend these. In this experiment, you’ll record EMG signals while performing precise hand movements, giving you a window into how neural signals shape motion. Movements in different directions recruit different muscles — and you'll see this live on your screen!

Procedure

  1. Electrode Preparation:

    Electrode Preparation:

    1. Attach red alligator clips to brass fasteners on the popsicle stick electrode.
    2. Attach the black clip to the ground screw.
    3. Apply conductive gel on the electrode sites.
  2. Electrode Placement:

    Electrode Placement:

    1. Place electrodes on the back of your hand, between knuckles.

  3. System Setup:

    1. Connect the electrode cable to the SpikerBox.
    2. Connect the SpikerBox to your smartphone or computer with the Backyard Brains app.
  4. Record Signals:

    Record Signals:

    1. Move your fingers up and down and side to side.
    2. Observe EMG signals for different movement types.
    3. Try small contractions to isolate single action potentials.
Results & Analysis

Results & Analysis

Compare EMG traces for up-down vs. side-to-side finger movements. Can you distinguish unique patterns?

Small contractions should show smaller spikes, while larger ones increase spike frequency and size. Try adjusting electrode placement for clearer signals. Reflect on how neural firing patterns control movement strength and precision.