Which Part of the Brain Activates the Stress Response

Which Part of the Brain Activates the Stress Response

Which Part of the Brain Activates the Stress Response

Which part of the brain activates the stress response

We all react differently to different situations. Have you wondered how the human body identifies a stress situation and how it needs to react to the stress?

Our body acts and reacts based on the instructions given by our brain. So, it is not surprising to know that our responses to stress are also activated in the brain. Which part of the brain takes care of this? Keep reading to know more about this:

When do you feel stressed?

Some situations that are bound to create stress in all people are some life-changing situations such as the death of a family member, permanent loss of a job, permanent disability in an accident, moving to a new location, being diagnosed with a serious ailment and the like.

The responses to these stress situations are classified broadly into two types – fight or flight.

How do you know you are stressed?

As soon as you are faced with a situation that doesn’t fall under your comfort zone, you feel stressed. The brain starts processing the information to identify if the situation is something that you need to feel stressed about or not. It is also intelligent enough to compare previous situations to assess how you reacted to a similar situation in the past.

When the situation is indeed recognized as stressful, you will automatically feel certain biological reactions such as increased breathing, a rapid increase in your heartbeat, reduced appetite, increased anxiety or a sense of fear, etc. Here is how certain parts of the brain activate these stress responses.

The Brain & its role on the activation of the stress response

The stress response of humans is classified into two important types – short term & long term. Different parts of the brain control different stress responses.

While the long-term stress response is activated by the Hypothalamic Pituitary Adrenal (HPA) System, the short-term stress response is activated by the Sympathomedullary Pathway (SAM).

How does the HPA work?

Regardless of the type of stress response that is activated, two important parts of the human system play an important role in this process. They are the pituitary gland and the adrenal medulla.  Here, let us see how these work in the HPA system.

The hypothalamus is present at the base of the brain. When a situation is identified as stressful, this sends signals to the hypothalamic-pituitary axis. How is stress identified and how is the HPA axis activated? This is because of a part known as the amygdala.

The amygdala is located right in the middle of the brain and it is as small as the size of a kidney bean. The stressors are identified accurately by the amygdala. The power of this small kidney bean-sized structure is such that it can identify all kinds of stressors with perfection.

When the amygdala identifies something like an emotional stressor, your brain will automatically trigger some emotions such as fear, sadness, anxiety, depression, etc. When the amygdala identifies something like a biological stressor, you will feel stress because of something that happened in your body – like an injury.

Does that mean that the amygdala’s powers are enough to activate the HPA axis? Definitely, not! Though the amygdala identifies the stressors perfectly, it is important to know what kind of reaction it should bring out in a person.

This will ensure that you don’t get unnecessarily stressed or worried about a situation that is not too serious. This is where the prefrontal cortex comes into the picture.

Located in the front region of the brain, the prefrontal cortex helps to control our reactions towards the stressors. It sends the necessary signals to the brain after analyzing the intensity of the situation.

When a stressor is picked up the amygdala, the prefrontal cortex quickly assesses it to know how serious the situation is, before sending signals to the brain to activate the HPA axis.

This will propel the pituitary gland to produce the adrenocorticotropic hormone. Never underestimate the power of the pituitary gland. It is a very small size, almost the size of a pea, but it plays a great role in the stress response system of the human body.

As the pituitary gland secretes this hormone, the corticosteroid hormone starts to get produced by the adrenalin glands that are located on top of the kidneys. It is this hormone that helps you to manage long-term stressors perfectly by helping your body to produce a steady supply of blood sugar.

The corticosteroid hormone, also known as cortisol, is a stress hormone that stimulates the other parts of the stress response system. It is a hormone that plays the role of a messenger perfectly.

It sends the necessary information to the brain so that the brain can make an informed decision as to how you should react in a stressful situation. The cortisol hormone ensures there is an ample amount of blood sugar in the body.

High levels of blood sugar help you stay energized and improve your ability to withstand long-term stressors with ease & confidence.  This hormone gives power to your muscles and increases your breathing rapidly for you to absorb more oxygen than before.

How does SAM work?

The Sympathomedullary Pathway (SAM) is the one that activates the short-term stress responses. Here, when the brain identifies a situation as stressful, its base part, the hypothalamus goes on to stimulate the adrenal medulla, which is one of the important parts of the autonomic nervous system, or the ANS, as it is commonly known.

When a short-term stress response of fight or flight is activated, the adrenal medulla starts secreting the adrenalin hormone. When this hormone is produced in abundance, it will lead to certain biological changes in you such as increased heartbeats, increased sweating, reduced appetite, reduced digestion, etc.

Once the brain identifies that the stressful situation is over, the adrenalin hormones are back in control again. Therefore, the functionalities of the sympathetic nervous system are subdued, making you normal again.

 Other parts where the stress response system has an effect on

Now that you have understood the way the brain activates the stress response system and the parts that are responsible for the same, let us take a look at how this affects the other systems of the human body.

The Cardiovascular System

When you experience a stressful situation, you need to fight it or flee from it. While the course of your action would be decided by the brain, you also need some other systems to help you in the process. The main system that will get impacted by the functionalities of the stress response system is the cardiovascular system.

It is this system that is responsible for circulating blood and oxygen all over the body. The adrenalin and cortisol hormones that are secreted during the stress response system are responsible for the increased flow of blood and rapid breathing that you experience in a stressful situation.

The cardiovascular system comprises the heart and the lungs. Therefore, any change in the stress response system has a direct impact on the cardiovascular system. It is only because of this impact that you are able to feel a sudden improvement in your energy levels when you experience a stressful situation.

The Digestive System

One of the main symptoms of stress is reduced digestion. When faced with a stressful situation, your brain sends signals to the digestive system in such a way that your energy levels are preserved as much as possible.

Digestion is a process that requires a lot of energy as the food substances need to be broken down into small substances. During stress levels, your body’s digestion powers come down drastically, because the energy is needed for other reasons.

The cortisol hormone, which is activated during stress, is also responsible for the increased production of glucose in the blood. This is another reason why your body doesn’t digest foods well. When the stress levels are short-lived, this will not create any harm.

On the contrary, when the stress levels continue for a long time, it can lead to digestive problems such as Irritable Bowel Syndrome in the long run.

The Immunity System

When faced with a stressful situation, the brain sends signals to the other parts of your body, thereby making you prepared to fight or flee.

This sudden boost of energy & strength is also because of the increased sugar levels in the body. You have to take care that you manage your stress levels. If you experience chronic stress for a long time, this can weaken your immune system and cause serious ailments in you.


It is important that you know to regulate stress levels well. Your brain is designed well to activate the right stress responses at the right time. However, it is up to you to take certain steps to ensure that you keep stress at bay always.

Meditation, rest, relaxation and prioritizing your work are some of the ways in which you can reduce stress levels to a considerable extent.

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