The autonomic nervous system (ANS) is also called the involuntary nervous system. It regulates important bodily functions such as heart rate, blood pressure, sweating, temperature, pupil dilation, and digestion. The system allows us to react and adjust these functions without consciously thinking about them.
The ANS is further divided into two components: The sympathetic and parasympathetic nervous systems. These two systems work in conjunction to provide input to your body at all times, acting to decrease or increase activities.
In a healthy system, when it’s time to act or there is a perceived threat, the sympathetic will dominate, when there are no threats, the parasympathetic dominates.
SYMPATHETIC NERVOUS SYSTEM: FIGHT OR FLIGHT
The ANS directs your body’s rapid and involuntary response to strain, such as danger, disease, and exercise. It sends messages to organs, muscles, and glands to increase heart rate, dilate the bronchial tubes to your lungs, increase perspiration, and cause pupil dilation.
This “fight or flight” response is an evolutionary survival mechanism, enabling humans and other mammals to react quickly to life-threatening situations such as an oncoming car or a buffalo speeding towards them. But your body may also react during non life threatening stress too, like traffic jams, making a presentation at work, or family arguments.
While your body is busy responding to stressors, the SNS inhibits non-vital functions such as digestion and salivation to stop energy from going to those organs and focus it on saving your life or nailing that presentation.
The SNS does not calm you down after it’s wound you up though, that role is performed by the parasympathetic system.
PARASYMPATHETIC NERVOUS SYSTEM: REST AND DIGEST
The parasympathetic nervous system (PSNS) works in opposition to the sympathetic system, controlling the body’s ability to relax. It mainly function to downregulate the body using the vagus nerve, which sends impulses from the brain to the body and back. The PSNS works to tell your brain what’s happening within your body, instead of your brain telling your body what to do. It usually activates when you are feeling relaxed or in a mundane situation.
The PSNS slows your heart and respiratory rates, narrows pupils, and increases digestion. It’s called the “rest and digest” or “feed and breed” system as it conserves the body’s natural activities until after a stressful situation has passed. Once the danger is over, the PSNS returns the body to homeostasis.
AUTONOMIC NERVOUS SYSTEM AND HEART RATE VARIABILITY
Heart Rate Variability (HRV) is a measure of how the SNS and PSNS affect your heart beat. When your nervous system is balanced, your heart is constantly being told to beat slower by your parasympathetic system, and to beat faster by your sympathetic system. These mixed messages result in a constant state of variation in your heart rate. HRV is the variance in time between beats.
For example, if your heart beat is 60 bpm, the time between beats is likely not exactly 1 second. It may be 0.9 seconds between two beats and 1.1 seconds between two others.
When you have high heart rate variability, it means that your body is responsive to input from both the SNS and PSNS. This is a sign that your nervous system is balanced, and that your body is capable of performing at its best.
Conversely, a low HRV means that one branch is dominating and sending stronger signals to your heart than the other. This may occur during a race for example, when the SNS is focused on allocating resources to your legs (sympathetic activity) as opposed to digesting food (parasympathetic activity). But it may also occur when you’re tired or sick, leaving fewer resources available for tasks like exercising or giving a work presentation.
Essentially, if one system is dominating, it means the SNS has less ability to take over when it needs to, such as when you’re facing down a bear.
How to restore balance
Once we understand the difference between SNS and PSNS we can actively try to stimulate our PSNS. Here are 7 fixes to restore the balance between your SNS and PSNS.
1. Reduce Stress - Stress is ubiquitous. Good health depends on removing or reducing whatever stressors we can control, and reduce our reactions to those we can’t.
2. Meditation - We can’t remove all external stress. Meditation is the best way to decrease our reactivity to stress we can’t control. It teaches us to ignore triggers. It reduces our breathing, slows our heart, and decreases our blood pressure: all signs of PSNS activation. Meditations reduces lactic acid in our muscles, promoting recovery.
3. Massage - Regular massage has been shown to restore balance between SNS and PSNS. Massage makes us stronger, calmer, and more able to fight infection. By activating the PSNS, massage promotes recovery. It retrains the body to move more readily into PSNS even when we’re stressed.
4. Breathing - Breathing straddles the peripheral nervous system and the autonomic system. It happens automatically but we can also control it. We can hold our breathe for example, but we cannot stop our heart. Slowed breathing is a hallmark of PSNS. But it’s not just a symptom, it’s a signal. Slowing your breathing intentionally tells your SNS than things are okay. This activates the PSNS.
Daily breathing exercises will strengthen your lungs, improve your immune system, and decrease your resting heart rate. Here’s a simple way to activate your PSNS. Inhale for a count of 2. Hold that breathe for a count of 5. Exhale for a count of 7. Repeat.
5. Yoga - Like meditation, yoga will bring you into PSNS, It also bolsters your ability to decrease SNS activation when you are stressed.
Daily or weekly yoga classes, or even a quick yoga video at home, will improve your strength, flexibility and breathing.
6. Nutrition - Can what you eat affect your SNS/PSNS balance? Yes. Avoiding stimulants such as caffeine and sugar will facilitate PSNS. An anti-stress diet brings the right mix of protein, minerals and other nutrients to support PSNS.
7. Exercise - Yes, intense exercise, even the idea of it, stimulates our SNS. But regular aerobic exercise such as light jogging can actually decrease SNS activity and activate our PSNS. The key is moderation and measurement.