Physiological Response: Manifestations of the Autonomic Nervous System in Stressful Situations
What Is Stress?
Let’s start by defining stress. Various sources offer similar definitions, generally describing stress as a set of nonspecific adaptive responses of the body to the impact of different adverse factors. However, this definition doesn’t fully capture the essence of the phenomenon. In reality, stress is a reaction to any new stimulus to which we must adapt. This means it’s inseparable from learning and from existence itself. As Canadian physiologist Hans Selye, who discovered the general adaptation syndrome, once said, only death can free us from stress.
In this article, I’ll use the term “stress” to describe a significant, pronounced reaction to a stimulus, which is evident through sensory (perceptible) manifestations in the body. The physiological response allows our bodies to survive: when a stimulus is perceived and evaluated as dangerous, a series of changes occur in how the body functions. Hormones like adrenaline and noradrenaline are released into the bloodstream, triggering immediate physical reactions that strongly stimulate the body. This results in increased muscle strength, faster reaction times, heightened receptor sensitivity, a higher pain threshold, and greater endurance. To keep things simple, I’ll describe the essence of these changes without getting too technical.
The Autonomic Nervous System
Our survival is managed by the autonomic nervous system, also known as the vegetative nervous system. This part of the nervous system regulates the activity of internal organs, blood vessels, and both internal and external secretion glands. In dangerous situations, it works seamlessly, playing a leading role in adaptive responses. The autonomic nervous system (ANS) controls the organs of respiration, circulation, excretion, digestion, reproduction, as well as growth and metabolism. Functionally, the ANS is divided into the sympathetic, parasympathetic, and metasympathetic systems. We’ll focus on the first two.
Sympathetic Nervous System
The sympathetic nervous system is activated in moments of danger and mobilizes the body’s resources. Its activation is extremely rapid. It helps the body adapt to changing environmental conditions by altering the metabolic rate in organs and tissues. What changes occur in the body during high-intensity stress (i.e., danger)? Here’s a list, with most described below:
- Increased heart rate
- Changes in breathing, with faster inhalations and exhalations
- Reduced surface blood circulation (pale skin)
- Higher blood sugar levels
- Slowed digestion
- Weakened intestinal peristalsis
- Constriction of blood vessels in some areas and dilation in muscles
- Stopped saliva production
- Dilated pupils
- Erectile dysfunction
- Faster reflexes
- Tremors
- Increased sweating
- Tunnel vision
- Partial or complete hearing loss
Parasympathetic Nervous System
The parasympathetic nervous system maintains homeostasis, returning the body to normal functioning. It acts much more slowly. Its job is to restore the body’s resources and replenish energy reserves. It has a calming, relaxing effect on most bodily functions. Central nervous system and heart muscle excitability decrease, as do metabolic intensity, blood pressure, heart rate, and body temperature.
A Personal Example
I remember once walking home from the store with my five-year-old daughter. The walk took about 10 minutes, and I was carrying heavy bags. My daughter, playing around, decided to run ahead. She knew the way home and confidently ran forward. At first, I called out to her a few times without success, then quickened my pace to keep her in sight. When she turned the corner of our building, I felt anxiety kick in. My mind raced with thoughts that fueled my fear for my child. My heart started beating faster, my breathing quickened, and my palms got sweaty. I also clearly remember that when I reached our building, my daughter was calmly waiting for me on a bench by the entrance, and I was so relieved that I almost dropped the bags and felt weak all over.
What does this tell us? Our bodies react with sympathetic activation not only in cases of direct danger to ourselves but also when we feel anxiety about a potentially negative future—both for ourselves and our loved ones. This is likely an evolutionary mechanism found in biological beings with a long period of caring for their offspring.
Everyday Examples
You can probably recall a dozen or more situations when your body quickly responded to changing conditions under threat. For example, while driving in a near-accident situation, you might have reacted instantly—braking, accelerating, or turning the wheel. This isn’t just about your skill or experience, but also about the invaluable mechanism evolution has given us.
How the Systems Work Together
The sympathetic and parasympathetic systems work in coordination. When our body is excited by the sympathetic nervous system, the homeostasis “pendulum” swings to one side. The parasympathetic nervous system’s job is to bring it back. As you can imagine, our bodies react quickly to save our lives, but return to their original state much more slowly. That’s why, as verifiers, we can detect lies by observing signs of the autonomic nervous system. By asking someone questions, you can see how their body’s external manifestations change through sensory cues. Here are the channels you should pay attention to:
- Breathing
- Skin
- Salivation
- Voice
- Eyes