How does your body respond to stress? In this experiment, we explore how the autonomic nervous system regulates heart rate in “stressful” situations—like submerging your hand in ice-cold water!
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 use an ice-water bath (the "Ice Water Test"), to determine if this is a "fight or flight" or a "rest and digest" response.
Safety first: skip this test if you have a heart condition, high blood pressure, Raynaud’s or a history of fainting. Keep your hand in the ice water for up to 1–2 minutes, or take it out sooner if it hurts.
Materials:
Setup:
Procedure:
How does your heart rate change? Was it dramatic? Does it vary between trials or individuals? Discuss how these findings align with either sympathetic vs. parasympathetic control.
Draw the pathway from cold and pain receptors in the skin of your hand, up your spinal cord to your brainstem, and back out along the autonomic nerves to your heart. Label where your EKG electrodes recorded.
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: a cold stressor changes the heart's rate.
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 on the skin is sensed and sent to the brain, which changes the heart rate.
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 cold and pain receptors in the skin to the brainstem and back out to the heart: the autonomic nervous system linking brain and heart.
HS-LS1-3 Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.
Measure heart rate before, during and after an ice-water dip and watch it settle once the cold ends; baroreflex feedback helps limit the change, though this lab does not measure it directly.
2 Developing and Using Models
Draw the pathway from cold and pain receptors in your hand to your brainstem and back out to your heart.
3 Planning and Carrying Out Investigations
Record EKG before, during and after an ice-water hand dip, two or three trials.
4 Analyzing and Interpreting Data
Compare heart rates across trials and people.
5 Using Mathematics and Computational Thinking
Average the heart rate over repeated trials.
6 Constructing Explanations and Designing Solutions
Decide from your data whether the response fits sympathetic or parasympathetic control.
Cause and Effect
The cold stressor changes heart rate.
Stability and Change
Heart rate settles back after the stressor ends.
LS1.A Structure and Function
Feedback mechanisms keep internal conditions within limits.
LS1.D Information Processing
Sensory input from the skin drives an automatic response.
Backyard Brains mapping using the book's method. Not in the book.
Our hearts beat continuously to power our circulatory system, and if we listen closely, we can actually see and hear the electrical impulses that drive each contraction.
Discover the natural reflex in humans and mammals triggered by water immersion.
