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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.

Devices and Accessories4Related Experiments2

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.

Draw the pathway from your motor cortex through your spinal cord to the small muscles between your knuckles, and label where your electrodes recorded.

NGSS alignment

Performance expectations

  • MS-LS1-3 Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.

    Nerve and small hand-muscle subsystems interact to produce precise movement.

  • HS-LS1-2 Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

    Draw the pathway from motor cortex to the small hand muscles: brain and muscles as one system for precise movement.

Science and engineering practices

  • 2 Developing and Using Models

    Draw the pathway from your motor cortex to the small muscles between your knuckles and label where you recorded.

  • 3 Planning and Carrying Out Investigations

    Record EMG from the back of the hand during finger movements and small contractions.

  • 4 Analyzing and Interpreting Data

    Compare traces for up-down and side-to-side movements.

Crosscutting concepts

  • Structure and Function

    Different muscles serve different movement directions.

  • Patterns

    Each movement direction has its own EMG pattern.

Disciplinary core ideas

  • LS1.A Structure and Function

    Firing rate and motor-unit recruitment grade force.

  • LS1.D Information Processing

    Motor commands control strength and precision.

Backyard Brains mapping using the book's method. Not in the book.