What happens when the nervous system detects a threat?

When our body detects a threat, it sends a signal to the brain. The brain quickly sends a response back to the body. This response is immediate and involuntary. It happens before our logical, thinking brain even has the time to process whether this threat is real. 

Despite thinking of ourselves as civilized and evolved, humans are at our core still animals. We have evolved over millions of years to avert danger, conserve energy, and reproduce. It’s how our species survived. Every involuntary thing that our autonomic nervous system does is with the goal of keeping us safe and secure. 

Every involuntary thing that our autonomic nervous system does is with the goal of keeping us safe and secure.

So when you recognize that your body has shifted into a threat response, there is no shame in getting activated or “triggered”. The key is how we learn how to recognize those stress responses in the moment, and work with our unique nervous system to manage our behaviors and reactions to stress in a healthy way. 

What is the difference between sympathetic and parasympathetic nervous system states? 

The autonomic nervous system (ANS) has two dominant states: one that is deactivated, and one that is activated. 

• the parasympathetic nervous system is the deactivated state, sometimes called “rest and digest” (but also includes the “freeze or collapse” responses) and

• the sympathetic nervous system is the activated state, sometimes called “fight or flight” (although there are other stress responses including “fawn” and “attach”)

Your autonomic nervous system has two different states: one that is deactivated (parasympathetic), and one that is activated (sympathetic). 

When you are in a parasympathetic state of safety and relaxation, or “rest and digest” your body and brain are functioning optimally. Your heart rate and blood pressure are normal, your breathing is deep and relaxed, your digestion is improved, your muscles are loose and flexible.  Your pre-frontal cortex is firing away, allowing you to tap into your rational, creative, and social higher cognitive functions. It’s characterized by being open, curious, creative, and socially connected.

When you are shifted quickly into “fight or flight”, a sympathetic activated state of sensing danger, your body and brain change to repel or avert the threat.  Your heart rate and blood pressure rises dramatically, your breathing is quick and shallow, blood  moves to your muscles and extremities. Your body releases stress hormones including adrenaline, cortisol and norepinephrine. Your prefrontal cortex can shut down or be tampered, limiting your ability to access language, problem-solving, and social connection.

However, if the activated “fight or flight” response is not going to allow you to escape the danger or fight off your attacker, then your body will shift back into a parasympathetic state. Rather than being relaxed, it will continue to exhibit signs of stress under threat. This is what we call the the “freeze or collapse” response. 

What is Polyvagal theory?

Polyvagal theory was developed by Stephen Porges in the 1990s. He describes how the parasympathetic nervous system is actually comprised of two branches of the vagal nerve (hence the name “poly”, meaning multiple or many): 

• the first is “ventral vagal”, sometimes called “rest and digest”, which was described above, and

• the other is “dorsal vagal” which is characterized by an immobilized “freeze or collapse” response. 

This is also a deactivated state, but unlike the “ventral vagal” state of relaxation and connection, it is a “dorsal vagal” state of immobility, paralysis, and fear. In this state, your heart rate drops below normal, breathing is shallow and slow, blood moves away from your extremities and collects at the core, around the heart and lungs. Your metabolism and digestion, however, remain slow or stagnant. Your body releases chemicals designed to manage and dull pain, including endorphins and natural opiates. This is because the body has accepted that fighting off or avoiding the threat is no longer possible. It is preparing for impact and trying to mitigate the inevitable damage. 

No matter what your stress response is, your digestion tract slows down, your body releases stress hormones and neurotransmitters, and your pre-frontal cortex is hampered, priming you to be more instinctual and reactive rather than being thoughtful and responsive. This is a “knee jerk” reaction to your perceived threat.

No matter what your stress response is, your digestion tract slows down, your body releases stress hormones and neurotransmitters, and your pre-frontal cortex is hampered, priming you to be more instinctual and reactive rather than being thoughtful and responsive. 

Remember that these responses are instantaneous and involuntary! There is no need to beat yourself up over having this natural, normal reaction. They key is not to try to always stay in a calm “rest and digest” state, but rather to become aware of the constantly shifting and evolving states that are in play within our nervous systems, and how they might create impulses and behaviors. In time, we can learn to befriend our nervous system and work with it, rather than seeing it as an adversary, trying to suppress it, or work against it.

In time, we can learn to befriend our nervous system and work with it, rather than seeing it as an adversary, trying to suppress it, or work against it.

Let’s summarize:

In the previous post, we’ve covered how the Nervous System includes the brain, spinal cord, and all the nerves throughout and within your body. I’ve explained the difference between the Somatic Nervous System, which is voluntary and controls muscle movement and sense of touch, and the Autonomic Nervous System, which is mainly involuntary and controls basic internal bodily functions like heart rate, digestion, and sleep. 

In this post, we got to dive into the parasympathetic and sympathetic nervous systems, both a part of the Autonomic Nervous System, and the different branches of the parasympathetic nervous system according to Polyvagal theory as developed by Stephen Porges. It’s important to remember that the parasympathetic nervous system include both deactivated states “rest and digest” as well as the “freeze or collapse” response.

It’s important to remember that the parasympathetic nervous system include both deactivated state of “rest and digest” as well as the “freeze or collapse” response to stress.

In the next blog, I’ll go further into what characterizes each of these states, what feelings or symptoms may accompany them. And believe it or not, there are actually more threat responses that we haven’t even covered yet! They include the “fawn” and “attach” responses. These are states that have to do specifically within social context and settings.  I’ll cover those in the next blog, too.