Experiment: Autonomic Nervous System

Human

Grade 6+

Autonomic Nervous System

How does your body respond to stress? In this experiment, we explore how the sympathetic and parasympathetic divisions of the nervous system regulate heart rate when placed in "stressful" situations—like submerging your hand or face in cold water!

What Will You Learn?

How the autonomic nervous system (sympathetic and parasympathetic) regulates heart rate.
How to record and analyze EKG signals using a Human SpikerBox.
How cold-water immersion (hand and face) can induce different physiological responses.

Background

Our nervous system isn’t just in our heads—it runs throughout the entire body. This extensive network allows the brain to coordinate far-flung bodily functions. Think of times when you’ve felt anxious or stressed: you may experience a racing heart, sweating, and that “butterflies in your stomach” feeling. The body prepares you for action!

Now think of how you feel after a huge holiday meal—tired and relaxed, almost lulled into a restful state. Your body and brain interact continuously, modulating responses to keep everything running smoothly.

In this experiment, we’ll create brief, safe stressors to observe how the body’s autonomic nervous system responds. We’ll first use an ice-water bath (the "Ice Water Test"), then examine the "Diving Reflex" by submerging the face. Both tasks trigger measurable changes in heart rate, illustrating how the sympathetic ("fight or flight") and parasympathetic ("rest and digest") systems balance one another.

Sympathetic vs. Parasympathetic

Experiment 1: Ice-Water Hand Submersion

Materials:
• A large container (bucket/bowl)
• Ice cubes + cold water (roughly a 3:4 ice-to-water ratio)
• Human SpikerBox and EKG electrode patches
• Towel for drying off

Setup:
1. Fill the container 3/4 full with ice, then add cold water until the mixture is near 0° C (32° F).
2. Place EKG patches on each upper forearm near the elbow and a ground patch on the back of one hand. Connect alligator clips from the SpikerBox: red leads to the upper forearm patches, black lead(s) to the ground patch.
3. Launch your recording software (SpikeRecorder), verify the SpikerBox is recognized, and note your resting heart rate.

Submerge your hand. Carefully place your hand in the ice water (keeping the electrode patches and SpikerBox dry above the forearm).
Record heart rate. Keep your hand immersed until it becomes quite uncomfortable. Then remove your hand and immediately note your heart rate.
Rest and repeat. Warm your hand back up, let your heart rate settle, and then repeat 2–3 times, logging the data to get an average.

You should see an increase in heart rate, reflecting the body’s sympathetic response to sudden cold stress. How dramatic is the change? Does it vary between trials or individuals?

Experiment 2: Diving Reflex (Face Submersion)

Materials:
• A container large enough for your face
• Cool or moderately cold water (NOT ice water)
• Human SpikerBox and electrode patches

Setup:
1. Empty the ice water and replace with cool (but not freezing) water.
2. Keep the same EKG electrode placement (upper forearms + ground on the hand).
3. Record a baseline resting heart rate, then hold your breath.

Submerge your face. Gently dip your face into the water. A partner should monitor your heart rate. Remain submerged as long as is comfortable, still holding your breath.
Record the heart rate. Observe the changes as soon as the face contacts cold water, and note if/when heart rate decreases. Then remove your face and breathe normally—does the heart rate rise again?
Repeat. Rest a bit and repeat 2–3 times to get consistent data.

You’re observing the diving reflex. Many mammals (e.g., seals, whales) rely on this reflex to slow heart rate, preserve oxygen, and ensure blood flow to vital organs. Even humans retain this protective response!

Results & Analysis

Compare your average heart rate before, during, and after each cold-water test. Do you see a clear increase in heart rate in the ice-water hand test? Did the diving reflex trial produce a decrease in heart rate? Discuss how these findings align with sympathetic vs. parasympathetic control.

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