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 underwater submersion can induce different physiological responses.
The Diving Response: How Your Heart Reacts to Water
How does your body react to being underwater? In this experiment, we explore how the nervous system responds when you submerge your face in water, triggering a unique physiological reaction!
About the Experiment
Background
Our bodies are constantly responding to the environment, making adjustments to keep us balanced, safe, and functioning efficiently. Some of these responses happen so quickly and automatically that we don’t even realize they’re controlled by our nervous system. Think about times when you’ve felt startled—your heart might race, your breathing quickens, and you feel an instant surge of energy. Other times, like after a big meal, you might feel relaxed, sluggish, and ready to rest. These changes are driven by two key divisions of the autonomic nervous system: one that prepares you for action and another that helps you recover and conserve energy.
In this experiment, we’ll test how your body reacts to being submerged in water. By measuring heart-rate changes, we’ll investigate how the nervous system adapts to different conditions and explore what this tells us about the way our bodies maintain balance in challenging environments.
Experiment
Across the Animal Kingdom
The way your body reacts in this experiment isn’t unique to humans—it’s a trait shared by many mammals! Whether it’s a human, a dolphin, or a seal, the nervous system triggers similar responses when submerged in water. As you observe your own body’s reaction, you’re witnessing a survival mechanism that has evolved across species to help conserve oxygen and adapt to underwater conditions.
Experiment
Diving Reflex (Face Submersion) Experiment
Safety first: skip the face dip if you have a heart condition or have ever fainted. Never hyperventilate (breathe fast and deep) before holding your breath, and come up whenever you need to.
Materials:
- Container large enough for your face
- Cool or moderately cold water (not ice water)
- Human SpikerBox & electrode patches
Setup:
- Fill the container with cool water.
- Place EKG patches on each upper forearm; ground patch on the back of the hand.
- Record a baseline resting heart rate, then hold your breath.
Procedure:
- Submerge your face. Gently dip your face into the water. A partner monitors your heart rate.
- Record heart-rate change. Observe the drop while submerged, then watch it rise once you breathe again.
- Repeat. Rest and run 2–3 trials for consistent data.
Results & Analysis
Compare average heart rates before, during, and after submersion. Did the diving reflex slow the heart? Why is that vital for diving animals? Discuss how your findings align with sympathetic versus parasympathetic control.
Draw the reflex loop: cold receptors in your face, the trigeminal nerve, your brainstem, the vagus nerve and your heart. Label where your EKG electrodes recorded.
Alternatives to Dunking Your Face
Perhaps not everyone wants to submerge their face in water, but we can still activate the same physiological response using other methods. One effective alternative is placing a cold, wet towel on the forehead, cheeks, and under the eyes. This still targets the trigeminal nerve, which plays a key role in signaling the body to adjust its heart rate and circulation in response to cold exposure.
By using cold towels instead of full immersion, we can still observe the body’s natural reaction to water, making it a practical and accessible way to study this reflex in different settings!
NGSS alignment
Performance expectations
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MS-LS1-3 Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.
Nervous and circulatory subsystems interact: cold on the face slows the heart.
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MS-LS1-8 Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories.
Cold water on the face is sensed and sent to the brain, which slows the heart.
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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 reflex loop from cold receptors in the face through the brainstem to the heart: nerves, brain and heart acting together.
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HS-LS1-3 Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.
Compare heart rate before, during and after face submersion: a reflex that conserves oxygen, then lets the heart recover.
Science and engineering practices
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2 Developing and Using Models
Draw the reflex loop from face to heart and label where you recorded.
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3 Planning and Carrying Out Investigations
Record EKG at rest, during face submersion and after, two or three trials.
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4 Analyzing and Interpreting Data
Compare heart rates across the three phases.
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5 Using Mathematics and Computational Thinking
Average heart rate before, during and after.
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6 Constructing Explanations and Designing Solutions
Explain why the slowdown matters for diving animals and whether it fits sympathetic or parasympathetic control.
Crosscutting concepts
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Stability and Change
Heart rate drops, then returns once you breathe again.
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Cause and Effect
Cold water on the face triggers the slowdown.
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Systems and System Models
Face receptors, brainstem and heart form one reflex loop.
Disciplinary core ideas
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LS1.A Structure and Function
Feedback mechanisms adjust heart rate to conditions.
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LS1.D Information Processing
Cold sensed by the face's nerves drives an automatic response.
Backyard Brains mapping using the book's method. Not in the book.
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