Which nervous system is being activated during a life threatening situation?

Most of us fear the things that are legitimately dangerous in life: driving on an icy road during a winter storm, standing at the edge of a huge cliff, or encountering a predatory animal like a snake or bear in nature. In other words life-threatening events.

introducing the Fight or flight response

How do we know what not to fear?

Most of us fear the things that are legitimately dangerous in life: driving on an icy road during a winter storm, standing at the edge of a huge cliff, or encountering in nature a predatory animal like a snake or a bear. In other words, we tend to be wary of life-threatening events. 

But what about those things that cause us fear but aren’t really dangerous? For example, going to a big social event, giving a presentation to a large group of people, or getting on a plane can trigger the body to produce stress hormones. We need to try our best to ensure that this response is triggered as seldom as possible. 

Our bodies are built to help us handle truly dangerous situations or even life-threatening situations. The response — called fight or flight — that occurs when we are in these situations helps us move faster, better, and stronger. Used sparingly, the physical symptoms, and the response triggered by fight-or-flight won’t hurt us.

Unfortunately, when the response is activated too often, those repeated physical symptoms can hurt us. 

Ahead, we’ll discuss how you can essentially learn to turn that fight-or-flight response off when it doesn’t need to be in use. First, it’s important to know why and how fight-or-flight happens and what triggers the stress hormone production. So, let’s begin there.

What Is Fight Or Flight?

Walter Bradford Cannon, an American physiologist at Harvard in the early 1900s, originally coined the term “fight or flight.” The American Institute of Stress1 defines the fight or flight response as, 

“A physiological response to stress  that occurs in the presence of something that is terrifying, either mentally or physically.”

Once the mind acknowledges the presence of something terrifying, the release of certain hormones is at the heart of activating the fight and flight response. From there, the sympathetic nervous system takes over, causing physical changes in your body that prepare you to either fight or flee. We’ll go over both of these physiological processes further on.

Why Is Fight or Flight Important?

The fight or flight response keeps you safe, just as it did for all of our ancestor's thousands of years ago. When you are faced with serious and imminent danger, it is imperative that your body be able to react quickly and effectively, through this physiological response.

For this reason, the fight or flee response is not something that we consciously control (for the most part). Rather, it is an automatic response that occurs within our brains and bodies essentially without our consent, an acute stress response. Much like the anti-lock braking system on your car that automatically pumps in short bursts when the vehicle encounters a patch of ice on the road.

The Science Of Fight Or Flight

Next, we will break down some of the science behind fight or flight response and what happens to the body, to your hormones, to the nervous system, and to which nervous systems are activated. Also, we'll take a look at how you could get out of the fight or flight response.

What Happens To The Body During A Fight Or Flight Response?

The fight-or-flight response starts in the brain. Before the physical reactions of this process can take place, your brain needs to recognize that there is a clear and present danger. This happens with help from your senses and from there, through a series of hormone releases. 

Your eyes and ears are the first of your senses to notice danger. In this case, let's say the danger is a grizzly bear that you encounter while on a hike in the woods. Your eyes see the bear, and your ears hear it rustling toward you through the bushes. These two senses send signals to your brain. Specifically, they are sent to your brain's emotion processing center,  the amygdala.

Next, the amygdala processes the information received from the eyes and ears. It informs the hypothalamus, a part of your brain that's often called the command center, that there’s immediate danger afoot. Your hypothalamus controls the autonomic nervous system (more on this later). It alerts the autonomic nervous system by way of a system called the HPA Axis.

The HPA Axis

The HPA Axis, or hypothalamic-pituitary-adrenal axis, involves a series of glands that are part of the nervous and endocrine systems, which are involved in fight or flee.

Everything starts with the hypothalamus — remember, this is the command center of the brain. The hormonal process goes like this:

1. The hypothalamus sends a hormone called CRH (corticotropin-releasing hormone) to the pituitary gland, which is also in the brain.

2. This hormone signals to the pituitary gland to secrete a hormone called ACTH (adrenocorticotropic hormone) and to send it to the adrenal glands. 

3. The adrenal glands are located on top of the kidneys. Once these glands receive the ACTH message from the pituitary glands, they are prompted to release another hormone called cortisol, the quintessential stress hormone.

4. At this point, cortisol, along with direct actions carried out by the autonomic nervous system, causes numerous changes within the body — all of which help you handle the situation of, for example, a bear trundling towards you in the woods.

The Autonomic Nervous System

The autonomic nervous system is a functional division of the broader nervous system that each of our bodies possesses. It is made up of two subsystems that oppose each other’s functions - the sympathetic and the parasympathetic nervous systems. The sympathetic nervous system takes on the responsibilities of fight or flight anxiety using the cortisol produced by the adrenal glands. This is termed the cortisol stress response. So the sympathetic nervous system and anxiety go hand in hand.

When discussing the autonomic nervous system, the keyword is autonomic, which means involuntary or unconscious. It’s an important concept to note because it tells us that this particular division of the overall nervous system is autonomous or acts on its own. In other words, you don’t need to tell your autonomic nervous system to do its job — nor can you.

The autonomic nervous system has the power to control three types of cells in the body:

• Gland cells. 

• Cardiac muscle cells. 

• Smooth muscle cells. 

For purposes of explaining fight or flight, let’s take a closer look at the two main subsystems that make up the autonomic2 nervous system: the sympathetic nervous system and the parasympathetic nervous system.

About The Sympathetic And Parasympathetic Nervous Systems

The Sympathetic Nervous System: In Charge of Fight and Flight

The sympathetic nervous system (SNS) handles the fight or flight response. 

This system is located in the middle portion of the spinal cord and surrounding area. From here, it connects to various tissues throughout the body; those that are connected to the three types of cells controlled by the overall autonomic nervous system. Remember those? They are the gland, cardiac muscle, and smooth cells.

The Parasympathetic Nervous System: In Charge of Rest and Digest

The parasympathetic nervous system (PNS) handles what’s referred to as the rest and digest response (more on this below).

In contrast to the central location of the SNS along the spinal cord, the PNS acts via either cranial nerves or the bottom of the spinal cord. From there, it is also connected throughout the body to the various glands, cardiac muscles, and smooth cells, which it can control autonomously. One of the most crucial cranial nerves involved in parasympathetic functions is called the vagus nerve.

How Is The Sympathetic Nervous System Activated?

Going through some kind of physical reaction that triggers the fight or flight anxiety, making your body aware of the danger, the amygdala proceeds by sending signals to the hypothalamus for it to activate the sympathetic nervous system. Relaying these signals through the autonomic nerves to the adrenal glands, triggers them to pump the hormone epinephrine (also known as adrenaline) into the bloodstream. That is how the sympathetic nervous system is activated. Is stress sympathetic or parasympathetic? The answer to that is sympathetic.

Fight or Flight Vs. Rest And Digest

Fight or flight and rest and digest are both systems that can occur at any given time within your body. In fact, they often take turns depending on your situation and state of mind.

Let's take a look at how they work in relation to each other.

You’ll notice that both of these systems control smooth muscles. It’s crucial here not to confuse these muscles with skeletal muscles.

Skeletal muscles are those that you are probably most familiar with. They are attached to your bones and joints. They are what you work out at the gym. They are what contribute to your overall shape.

Skeletal muscles are also voluntary, which means we consciously decide when they move (for the most part). You'll recall that smooth muscles, by contrast, are involuntary. We can't control them. 

This makes sense. After all, smooth muscles aren't connected to our bones or joints. Rather than our organs. Specifically, they are located within the organs of the digestive system. This means they are essentially in control of how food moves through the digestive organs like your stomach and intestines. 

Smooth muscles also surround blood vessels, which means they can dictate where blood flow moves within your body.

Why Is This Important?

Well, it’s important because both the SNS and the PNS have dominion over these smooth muscles (as well as cardiac muscles and glands). Therefore, how these muscles operate on a regular basis will depend on which system (the SNS/fight or flight system or the PNS/rest and digest system) is active.

Example of the Sympathetic Nervous System at Work

Let's say you woke up in the middle of the night after hearing a large crash of glass in your living room. You are on high alert. It's safe to say that your sympathetic nervous system or your fight or flight system is now in charge. 

Although there's no way of knowing that these functions are going on when you are in this state, your sympathetic nervous system is sending all sorts of messages to the cells it controls.

In terms of your heart, the SNS will, for instance, manipulate the smooth muscles around your digestive organs to send blood away from digestion and to other muscles that are more important right now, namely, those skeletal muscles that help you move. Digestion simply isn’t a priority right now. 

At the same time, the SNS manipulates your cardiac muscles (remember, it controls those too) to boost your heart output. This essentially makes your heart pump harder and faster. 

Finally, your SNS sends messages to your gland cells. For example, it will manipulate the sweat glands to produce more sweat, which helps cool you down and keeps you moving when and as you need to in this difficult situation

More Physical Symptoms of Fight or Flight

Other reactions may occur when your fight or flight (SNS) system is active as well. What is a physiological response? Basically a physical reaction to the situation. What are some physiological responses, your SNS can trigger:

Let’s look at another example. 

Example of the Parasympathetic Nervous System at Work

Say you’ve just returned home from a long day at work, during which you had to give a big presentation. It went great. You got an amazing review. Now it’s over, you’re home, and that's when the activation of the parasympathetic nervous system happens.

It’s easy to see that your PNS should be active. You are resting and digesting, conserving and storing energy. There are no threats, and you are in a state of what Walter Bradford Cannon called homeostasis in his book The Wisdom of the Body, published in 1930. Homeostasis3 is the state of equilibrium necessary for survival.

When homeostasis is going on internally in your body, those smooth muscles, cardiac muscles, and glands are still being activated. But remember that they are not being controlled by the fight or flight system (SNS) anymore. Instead, they’re being managed by the rest and digest system (PNS). 

Because of this, resting and digesting are priorities:

• Smooth muscles move more blood to the digestive system and away from skeletal muscles. 

• Cardiac muscles calm down, allowing the heart to pump more slowly and less hard.

• Sweat glands don’t overwork to produce more sweat. 

More Physical Symptoms of Rest and Digest

During times when the parasympathetic nervous system is active, your body works to conserve energy, and many positive things happen. For example, in addition to the changes in your heart, digestive system, and sweat glands outlined above, the following will also occur:

• Breathing slows down.

• Skeletal muscles relax.

• Blood pressure decreases.

• Saliva production increases (to aid in digestion).

Remember the vagus nerve? It modulates many functions of the digestive system, forming what is known as the gut-brain axis. This axis is two-way (i.e., from the brain to the gut and from the gut to the brain and has many health-related implications.

What Hormones Are Released by the Parasympathetic Nervous System?

When it comes to the heart rate in the body, it is controlled by the two branches of the autonomic (involuntary) nervous system. The sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). Hormones released by SNS consist of catecholamines, epinephrine (adrenaline), and norepinephrine which all contribute to an accelerated heart rate. When it comes to the parasympathetic nervous system PNS has the opposite effect of SNS, so instead of increasing the heart rate, it reduces it with the hormone acetylcholine. The parasympathetic nervous system activation is essential for everyone that has gone through the SNS process. 

In addition to the things mentioned above, PNS basically undoes what the SNS has caused. Historically and clinically, acetylcholine (ACH) is arguably the most important neurotransmitter known.

Chronic Stress And Fight or Flight

It’s easy to see that the fight or flight response is essential in some situations. Undoubtedly, your body's ability to manipulate the smooth muscles, cardiac muscles, and glands in order to produce quicker, faster, and stronger reactions when you need them can save your life.

However, it’s also easy to see that if you are unable to perceive truly dangerous situations accurately, you may ignite your fight or flight response more often than is necessary. The point here is that you do not want your fight or flight system to be activated when it doesn't need to be.

Producing excessive sweat is helpful if you need to run away from a bear, but it’s not so great when you’re trying to make a good impression on a first date.

Having your heart pump faster and stronger is helpful if you need to lift a fallen limb off of someone who’s hurt, but it's not productive when you're sitting at your desk trying to finish up a report. Both of these are physiological responses to stress.

Original research by David S. Goldstein in the journal Cellular and Molecular Neurobiology4 states, “If the stress response is excessive or prolonged then any of a variety of clinical disorders can arise.”

In other words, the fight or flight response keeps us alive when activated for a short period of time at the expense of long-term well-being. However, initiating the fight or flight response too often can have serious health ramifications.

The Consequences Of Chronic Stress

Long-term, frequent activation of the fight or flight response is often synonymous with a health phenomenon called chronic stress. 

Chronic stress occurs when, “your stress system stays activated over a long period of time … The constant rush of stress hormones can put a lot of wear and tear on your body, causing it to age more quickly and making it more prone to illness.”

Fortunately, there are ways to handle chronic stress — or the false perception that non-dangerous situations warrant the fight or flight response.

Managing Stress And The Fight Or Flight Response

If you were asked at this point which system (the sympathetic or the parasympathetic) you would want to be more active most of the time, what would you answer?

Undoubtedly, the correct response would be the parasympathetic nervous system. Naturally, since it is this system that gives us that cool, calm, and collected feeling. 

But how can we encourage the parasympathetic nervous system and discourage the sympathetic nervous system when there is no true danger? 

We can do this by cultivating better stress management in our daily life. Here are several strategies to start with:

Long-term “Fight or Flight” Stress Management Strategies

1. Restorative Yoga

Restorative yoga is a physical practice that helps your mind, body, and spirit slow down and relax. If you have considered trying a yogic practice, restorative yoga is a great place to begin and a perfect tool to combat the physiological response to stress. While other types of yoga may be more active and animated, restorative yoga tends to be slower. It often uses props such as bolsters, blankets, and blocks. 

Poses are held for longer and some of the goals are to increase flexibility and strength. But it’s also about calming the mind. Many people say that after taking a restorative yoga class, they felt like they hardly moved at all. Unlike other contemporary yogic practices, these long holds can help you relax more deeply and allow your muscles and joints to restore themselves in amazing ways.

2. Yoga Nidra

Yoga Nidra is an ancient yogic practice that puts practitioners into a state of near-sleep. Through guided meditation by a professional practitioner, users of Yoga Nidra can achieve an extremely peaceful and intense state of relaxation that balances you on the very edge of sleep but not quite into dreamland.

Yoga Nidra can be practiced with an individual guide who can take you through the steps of achieving this mental state. It can also be done alone with help from a recorded guided meditation. Finally, you can take Yoga Nidra classes with a teacher who will lead your entire group.

3. Meditation Practice

Meditation is one of the best ways to improve your stress response, lower overall anxiety in your life, and live more peacefully. It is definitely a way to help yourself reduce the occurrences of fight or flight and to activate your parasympathetic nervous system.

Many people are intimidated by meditation. However, meditation should not be something you fear or worry about accomplishing or doing absolutely correctly. You cannot accomplish meditation. It is a practice that goes on and on and one that you can cultivate as a lifelong activity. One that will provide endless benefits and will help reduce physiological stress. 

While there are certain protocols for different types of meditation and guidelines that you can use as you're just starting out, anyone can decide to become a meditator at any time. You can meditate for hours at a time, but you can also do it for two minutes or ten minutes. 

For the most part, there are two types of meditation: sitting meditation and walking meditation.

Sitting meditation is generally where people start. You can meditate alone, with a partner, or in a group. You can practice it by using your own knowledge about meditation, or you can have a guide or teacher help you along.  It can be silent, or it may be accompanied by audible guidance from a teacher. You may decide to use a meditation cushion, a chair or to sit on the floor or even on the edge of your bed. 

The benefits of meditation are profound and can be seen both scientifically and empirically, with one of the biggest ones being the reduction of physiological stress.

While many people think that the goal of meditation is to sit silently for long periods of time without thinking, without blinking, and without allowing your mind to waiver even for one moment, this couldn't be further from the truth. In actuality, meditation is simply about attempting to concentrate on a chosen focus (such as the breath or a mantra word or phrase) while noticing all of the thoughts, feelings, emotions, sounds, and sensations that come your way —and many of these things will surely come your way!

4. Daily Mindfulness Practice

Mindfulness is the practice of living each moment as it comes and focusing on them fully. In this day and age, many distractions cause us to be unable to concentrate and focus on one activity at a time. 

Mindfulness promotes mono tasking — or doing one thing at a time, slowly, effectively, and mindfully.

To do something mindfully means to pay full attention to it and to embrace everything about it. You can do anything more mindfully — from washing dishes or sweeping the floor, to driving to work or playing with your children. And this doesn’t only go for you. There is also Mindfulness for Kids and Mindfulness For Teens to help them become more mindful in their life.

5. Tai Chi

Many people find that movement helps them concentrate better when it comes to meditation. If sitting meditation tends to be a challenge because of its motionlessness and stillness, you might try tai chi.

Tai chi is also especially good for those who suffer from chronic pain or illnesses and for the elderly, as a way of getting exercise for both the mind and body.

Tai chi is an ancient Chinese practice and was originally a form of self-defense. However, today it is used to reduce stress and promote physical fitness. The practice is often done in a group with a leader. It is described frequently as meditation in motion. By using slow, gentle movements that flow from one to the next, tai chi helps your body stretch and exercise itself while your brain aims to focus on the breath and stay in the moment, watching each flowing movement as you perform them.

Breathing And Fight or Flight

As we encounter a stressful situation, say being chased by a grizzly bear, the sympathetic Fight or Flight response rapidly fires to send signals to the breathing system. To gain more oxygen for skeletal muscles, rapid but shallow breathing takes place. This is helpful when we are trying to get away from a predator, but becomes detrimental when we are chronically stressed. The forward direction is pretty clear - Fight or Flight activates rapid breathing, but what about the reverse direction? Can changes in breathing patterns influence the Fight or Flight response?

To answer this question, we need to think of the body as an integrated system. When we breathe in oxygen and exhale carbon dioxide, the pH of the blood changes. This change in pH is detected by special chemoreceptors. These send electrical signals to the autonomic nervous system, altering their functions. Since this system controls blood pressure, heart rate, and hormonal response, these physiological states will be altered as well.

In a study conducted by Alder et al., decreased muscle sympathetic activation is shown to be responsible for the reduction in blood pressure following the practice of slow breathing techniques. As the worthy opponent of SNS, PNS also plays a crucial role in breathing-induced changes. In addition to being part of the gut-brain axis, Kromenacker et al. discovered that the vagus nerve is key in mediating the beneficial physiological changes, such as reduced blood pressure and heart rate, that follow guided breathing exercises.

• Fight or flight -> shorter, more rapid, and shallower breathing. 

  • Helpful when trying to get away from a predator, but not helpful when chronically stressed

  • What about changing the breathing pattern to influence SNS?

• Body as an integrated system. 

  • breathing -> change in pH of the blood -> change in muscle sympathetic activity (SNS)/vagal activation (PNS) -> change in blood pressure/heart rate/etc.

SNS

• Device-guided slow breathing reduces blood pressure and sympathetic activity in young normotensive individuals of both sexes 

• slow breathing appears to be effective in young healthy normotensive individuals of both sexes and may be an ideal preventative therapy against future hypertension

• In both females and males, slow breathing reduced muscle sympathetic nerve activity and sensitized the cardiovagal efferent arm of the baroreflex.

• Interaction between the retrotrapezoid nucleus and the parafacial respiratory group to regulate active expiration and sympathetic activity in rats

• retrotrapezoid nucleus (RTN) contains chemosensitive cells that distribute CO2-dependent excitatory drive to the respiratory network, facilitating the function of the respiratory central pattern generator (rCPG) and increases sympathetic activity

PNS

• Role of the vagus nerve

• Vagal Mediation of Low-Frequency Heart Rate Variability During Slow Yogic Breathing

• changes in heart rate by slow-paced breathing are almost entirely vagally mediated, showing that slow-paced breathing is an effective tool for cardiac vagal activation

• Effect of selective vagal nerve stimulation on blood pressure, heart rate, and respiratory rate in rats under metoprolol medication 

• selective vagal nerve stimulation (sVNS) has been shown to reduce blood pressure without major side effects in rats

Fight Or Flight: Frequently Asked Questions

Can You Stop The Fight or Flight Response?

In a way. You'll remember that the fight or flight response is automatic. In other words, you can't actively control it the way you can control how your hands move or what you say.

On the other hand, you can trigger relaxation responses within yourself, which can help you overcome your stress response in times of immense tension. Naturally, you wouldn't want to do this if you were actually experiencing a danger. But if you're in a situation that doesn't warrant fight or flight freeze but still may be stressful, you can try relaxing with some of the techniques listed above. 

Additionally, when you don't have much time, deep breathing exercises and progressive muscle relaxation are particularly helpful in reducing the physiological stressors

Can Emotions Alone Trigger Fight or Flight?

Yes. In fact, this is a common issue for many people, and it is often referred to as panic attack disorder. 

With this disorder, racing thoughts or emotions (or sometimes, an initial triggering event followed by racing thoughts and emotions) can cause extreme physical reactions. These are essentially the same as those in fight or fright situations, such as a racing heart and quickened breathing.

How Long Does Fight or Flight Last?

The time can vary. Fight or flight begins right away. That's what it's meant to do: occur extremely quickly so that you can efficiently decide whether to stay or go when faced with danger. 

However, the situation will dictate how long the fight or flight hormones remain activated. Generally speaking, the adrenaline that has flooded your body during fight or flight freeze may remain for some time after the initial rush. That means it can take a while to come down from this automatic response and for the physiological stressors to subside.

Is Too Much Adrenaline Dangerous For You?

To be under some stress is normal and sometimes even good for you. But prolonged exposure to stress and the triggering of the stress hormone adrenaline can have harmful effects on your body. The prolonged epinephrine effects can result in higher blood pressure, increased risk of heart attack and stroke. To ensure your body doesn't produce too much adrenaline, you should make sure you reduce the amount of stress you put yourself under, as much as possible. The last thing you want is your body's physiological response to prolonged epinephrine effects as it could end up being lethal.

Don’t Live Your Life In “Fight or Flight” Mode

There’s no need to live your life in fight or flight mode. While it is sometimes a necessary function that offers immense benefits in times of danger, it is not a sustainable way to live on a regular basis.

For this reason, better stress management becomes absolutely essential. The approaches outlined above will provide you with a strong foundation to begin working actively against the recurrence of fight or fright when it’s not needed. The benefits of these approaches promote optimal physical and mental health in the face of regular stressors and the daily ups and downs of daily life.

What part of the nervous system responds to threats?

Which part of the nervous system is activated when a threatening situation is resolved?

Which part of the nervous system is activated when a person is in danger?

What nervous system is activated when frightened?