The Nervous System

OK so lets dive into the nervous system and take a look at how it works.  The nervous system has evolved and adapted to be able to manage and send information back and forth between the brain, the muscles, glands and organ systems.  Much of that information consists of interpreting outside stimuli. managing threats, completing voluntary tasks involving the muscles and regulating the complex interchange of hormones and organ homeostasis.  The nervous system is comprised of:

  • The Central Nervous system (CNS) is comprised of the brain and the spinal cord.
  • The Peripheral Nervous System (PNS) consists of all the nerves that branch out from the spine and brain and reach to our muscles and organs.

The Peripheral Nervous System can be divided up into two parts as well.

  • The Somatic Nervous System is responsible for our voluntary actions that cause the movement of our skeletal muscles.  Think of taking a pot off the stove.  We send conscious signals via the Somatic Nervous System to cause that action to happen.
  • The Autonomic Nervous System controls all our involuntary actions that regulate system such as heart rate, respiration and digestion.

We are going to focus closely on the autonomic nervous system which consists of fibers that send and receive regulatory signals.   The autonomic nervous system consists of two parts- the sympathetic and parasympathetic nervous systems.


Sympathetic Nervous System


The Sympathetic Nervous System  is associated with “Fight, Flight or Freeze”.  This is the main response to trauma or ongoing reaction to severe stressors.  With severe stress, the hypothalamus sends signals to the pituitary gland that then signals the adrenals to secrete stress hormones to respond to the threat.  The adrenals release cortisol and adrenaline in response to the threat.  This is known as the HPA (Hypothalamus-Pituitary-Adrenal) axis.

Cortisol causes blood sugar to be broken down from fat cells in a process known as gluconeogenesis.  This sugar is then circulated in the blood stream

to provide energy for either fight or flight.  Adrenaline is released that then causes an increased heart rate and blood pressure to rise so that blood is circulated more quickly to the visceral muscles.  Pupils are dilated, while saliva and gastric juice production is reduced radically.  Gut motility also stops as the body sees no need to digest when all systems are directed towards dealing with a threat.

Sympathetic nervous system responses are key for reacting to a significant threat. Evolutionarily this was important for protecting against a predator such as a wolf, jaguar or bear.  But if the perception of a threat persists for long periods, the sympathetic nervous system stays heightened for too long or too often.  The body starts to produce stress hormones that persists and leave the individual in a chronically elevated heightened state.  Nowadays we are dealing with multiple sets of stressors that can leave one stuck in a heightened sympathetic state.  In childhood that could be an angry abusive or alcoholic parent.   Oppression, poverty, and the stress of modernity could also have ongoing taxing effects on the nervous system- leaving us perpetually in a sympathetic dominant state.


The Parasympathetic Nervous System


The yin to the yang of the sympathetic nervous system is the parasympathetic reponse.  The parasympathetic nervous system is associated with the rest and digest (or feed and breed) portion of the nervous system.  This means that while the sympathetic portion of the nervous system is geared towards to responding towards threats and stressors, the parasympathetic is the counterbalancing portion of the nervous system that helps us to stay calm and relaxed.  Think of the S in sympathetic standing for Stress and the P in parasympathetic standing for Peace.

When the parasympathetic is dominant, heart rate slows, blood pressure reduces, pupils no longer dialte, saliva and gastric disgestive juices flow freely in preparation for eating meals.  The sexual organs allow for the free flow of blood through them to allow for intercourse.


Heart Rate Variability 


One of the key aspects of seeing how stress impacts us, one can look at one measure known as heart rate variability. This is literally the speed and rhythm of the heart rate.  Though intuitively we wold think that heart rate becomes more steady and regular when we are calm, it is just the opposite.  A healthy heart rate actually has small fluctuations in rhythm that is known as heart rate variability.  Though actual stutters and murmurs signal an unhealthy heart, small fluctuations, or variability, signal a healthy response to stress.   These fluctuations might mean your heart rate is changing subtly with heart beat intervals like this  1 second…1.08 seconds…..95 seconds…1.03 seconds…1..09 seconds…etc.  Increased variability signifies an adaptable heart and a healthy response to stress.  Those who are overwhelmed with stress or are highly attuned to it due to past trauma may have a much more even heart rate that signifies rigidity and more challenge in adapting to stress.  In essence, variability and fluidity are hallmarks of a healthy adaptive physiology.  For more about this fascinating topic please read my article Healing the Heart:  Exploring Heart Rate Variability and Trauma.


Polyvagal Theory


So even though I got through describing the autonomic nervous system as a binary, its not.  Fascinating research done by Dr. Stephen Porges point to a more complex nervous system.  let’s take a look.   The parasympathetic nervous system is mediated in part by the vagus nerve, the longest nerve in the body that stretches from the cranium down through the  back of the throat down to the main organs, the gut and reproductive system.  Because it touches most of the internal systems, it acts as a key mediator between the nervous system and the rest of the body.  The vagus sends chemical messengers to help shift us to a parasympathetic state and is key for the body to keep relaxed, heal and being able to digest and engage sexually.  There is even research that shows that certain bacterial strains send messages from the gut to the nervous system via the vagus.  In essence certain bacterial strains help us feel calm and relaxed.

Now Dr. Porges noted that the vagus has both a more primitive (dorsal) and more evolutionary new (ventral) portion.  The dorsal portion of the vagus is associated with the freeze response.  We already mentioned that the sympathetic nervous system is involved with responding to heavy stressors and threats.  It induces us to either fight or flee.  But if that threat is unmanageable then it may induce us to freeze (fight, flight or freeze).  Imagine a father who is abusive and angry and a child who can neither fight their dad or escape from him.  The threat may appear so overwhelming that the child freezes and dissociates.  We have all seen that when a deer freezes in the headlights or a lizard freezes when it knows it has been seen.  This is a primitive response that saves us from the full emotional and physical impact of that threat.  But if that trauma was very severe, or was ongoing for long periods, the likelihood of shifting into a freezes dissociative state becomes more easy in later life, even if the stressor or trigger appears pretty small.

But lets go a little further and bring in some polyvagal theory.  Imagine you are a small child crying out to your parents because you are hungry, cold, lonely or tired.  In a healthy household, a parent then comes running and soothes the child by holding them, cooing and looking at them in the eyes to reassure them.  In essence the parent is overriding the primitive response to stress through fight flight or freeze.  This overriding happens as the parent signals sensors in the face and the eyes to signal the ventral vagus to calm us down.  If a parent models this soothing behavior regularly, it becomes easier for the child to soothe himself as he gets older.  But if a parent neglects the cries of the child, or worse- comes in with anger and rage- the child does not learn how to override the sympathetic to calm themselves down via the vagus.  At a later age, that circuit becomes stuck towards a fight, flight or freeze state.

What Porges realized as that as mammals evolved, they developed this ventral portion of the vagus that could override a sympathetic nervous system to a perceived threat.  And we do this via connecting to other mammals of our same species.  For example, imagine being in a crowded movie theater.  Someone starts yelling and acting out intensely. Initially one may become frightened but if the individual looks around and sees people looking and talking about the situation calmly (“Oh he’s just drunk and he’s heading out the door anyway”) then the individual can override their sympathetic nervous system and sooth themselves via the ventral vagus.  So polyvagal theory teaches us that mammals can override primitive binary responses to threat by interacting with other mammals to self-soothe.  If we are taught this from an early age via healthy attachments, it becomes increasingly easy to do at a later age.  But if we are not taught to soothe our nervous system via parental healthy contact, then we can get stuck in patterns of trauma that persist.   For a much more in depth look at polyvagal theory, please read this my article Polyvagal Theory, Herbalism, Resiliency and Healing.


Herbalism and the Nervous System


Our goal as herbalists working with people who have an easily triggered sympathetic nervous system or those who are dealing with a great deal of stress, is to help teach the individual to shift from a sympathetic to parasympathetic dominant state.   And plants can do this in a number of ways.  From forest bathing, to smelling aromatic plants, to taking in relaxing nervines, or strengthening health gut bacteria that induce calm states, plants work in multiple ways to help shift us to a parasympathetic state.  When we encourage this change regularly, we are essentially teaching the nervous system to stay in a more relaxed parasympathetic dominant state.

One of the ways of describing this way of healing is to increase “vagal tone”.  Vagal tone means how well one can activate the vagus to induce a calm parasympathetic state.

Here are a few ways herbs can strengthen parasympathetic dominance:

Bitters:  Bitter herbs have a direct effect on the receptors in the mouth and digestive tract which then signal the vagus nerve to calm the nervous system.  In other words

Isabel with Oregon Grape

bitter plants are grounding by nature.

Some examples-

Nervine bitters:  Hops, chamomile, vervain, betony

Digestive bitters:  Yarrow, angelica, dandelion, burdock, Oregon grape.



Nervine Relaxants:  These herbs directly relax the body often by enervating the GABA receptors (the same ones that are targeted by benzodiazepines such as valium and xanax)

Examples:  Lemon balm, chamomile, kava, motherwort, passionflower

Burning a mugwort bundle


Aromatics:  These are herbs rich in volatile terpenes and phenols that can be taken in through inhalation, teas and tincture.  Aromatic herbs improve parasympathetic dominance via several pathways: through vagal stimulation, limbic stimulation leading to release of serotonin and dopamine, and GABA receptor stimulation.  

Examples:  lavender, douglas fir, rosemary, holy basil, hyssop, mugwort, oregano




Prebiotic Rich herbs:  These are herbs that help strengthen healthy populations of bacteria which then stimulate the vagus to induce calm.  In essence they provide food (prebiotics) for the bacteria so that they can grow and multiply.

Examples:  Prebiotic rich herbs include dandelion, burdock and elecampane root (inulin), seaweeds, medicinal mushrooms.



Outside of herbal approaches there are myriad ways to stimulate the vagus.  Here are a few:

Throat gargling

Deep Breathing




Tai qi/qi gong




The nervous system is a highly complex branched system consisting of the brain, the spinal cord and millions of bundled nerve fibers that extend throughout the body and send messages back and forth to respond to threats and regulate hormonal signaling and organ homeostasis.   Vagal toning exercises as well as certain herbal therapies can help improve resiliency and our ability to manage stressors.

Follow me on Instagram

Leave a Reply

Your email address will not be published. Required fields are marked *