The Stress Response and Anxiety Symptoms
Medically reviewed by Rae Harwood, M.A., B.N., EdD (Counselling Psychology)
Last updated June 13, 2019
The body is an incredible machine comprised of cells, tissues, and organs all working together to sustain life.
To keep the body functioning normally throughout our lifetime, the body uses its eleven organ systems (integumentary, muscular, skeletal, nervous, circulatory, lymphatic, respiratory, endocrine, urinary/excretory, reproductive, and digestive) to check and balance itself in an effort to maintain a relatively constant and stable state of internal balance (equilibrium). This process is called Homeostasis: a process that living things use to actively maintain stable conditions necessary for survival.
These systems work together to control body temperature, blood pressure, heart rate, respiration, PH balance, CO2 balance, and so on. These systems manage the body automatically in spite of the ever-changing internal and external conditions.
As long as we live a healthy lifestyle, such as eating a healthy diet, keeping stress to a minimum, getting regular exercise, and getting sufficient rest and good sleep, the body does a good job of maintaining itself, for the most part, all by itself.
The Nervous System
The nervous system is the body’s central command and communications network. It manages homeostasis by controlling and regulating all of the systems throughout the body. The nervous system is made up of an intricate network of fibers that connects every part of the body to the brain.
Every muscle we move and every tissue in the body is controlled or monitored by the nervous system. The nervous system not only keeps us informed about the world outside and inside of us but it also allows us to react to it. It’s also at the core of our thoughts, feelings, and actions, and is the mechanism responsible for our senses (sight, smell, touch, hearing, and taste).
“The nervous system is essential to sensory perception, the perception of pain and pleasure, the control of movements and the regulation of body functions.” It truly is the body’s most important network.
Nerve cells, called “neurons,” are the basic functional unit of the nervous system. They are specialized cells that have an electrochemical makeup (the combination of electricity and chemicals), which makes them unique in the body.
Neurons are responsible for picking up signals in one part of the body and sending them to another where they are relayed to other neurons or to bring about some specific action. They accomplish this task by sending and receiving “nerve impulse” (electric signal) information via the electrochemical process.
There are over 100 billion cells in the body’s nervous system (which includes the brain).
The nervous system consists of two main components that work together:
- the central nervous system (CNS), which includes the brain and spinal cord; and
- the peripheral nervous system (PNS), which links the CNS to all the nervous tissue in other parts of the body, such as the body's organs, muscles, glands, and receptors.
The peripheral nervous system (PNS) also consists of two components:
- the somatic nervous system (somatic PNS), which is under our direct control; and
- the autonomic nervous system (ANS), which is under involuntary unconscious control.
Somatic Nervous System (Voluntary)
The somatic nervous system has a dual role. It first collects information about the outside world from sensory organs (eyes, ears, nose, etc.) and transmits it to the CNS. Second, it sends signals from the CNS to the skeletal muscles, which initiate movement (such as directing the action of the arms, legs, head, and trunk). We can voluntarily use these nerves to do such things as raising an arm or moving a leg.
Autonomic Nervous System (Involuntary)
“The ANS innervates three types of tissue: glands, smooth muscle, and cardiac muscle. As such, almost every part of the body is a target of the ANS,…”
The hypothalamus, which is considered the command center of the brain, controls the entire autonomic system. The hypothalamus receives information about any variations in, for instance, the body’s chemical makeup, and adjusts the autonomic system to bring the body back to the right balance. Involuntary means we can't intentionally control these nerves; they respond automatically to internal messages as well as external messages as interpreted by our thoughts and emotions.
The ANS is the nervous system we want to focus on since it holds the keys to understanding how anxiety and stress affect the body.
Autonomic Nervous System is made up of three main components:
- The Enteric Nervous System (ENS)
- The Sympathetic Nervous System (SNS)
- The Parasympathetic Nervous System (PNS)
The enteric nervous system (ENS) is the nervous system that monitors and controls the gastrointestinal tract. It is often referred to as the “little brain” because of its unique neural system embedded in the lining of the esophagus, stomach, intestines, pancreas, and gallbladder.
With the number of neurons comparable to the number of neurons in the spinal cord, the ENS controls intestinal motility, fluid transport, blood flow, and nutrient handling. It is the only part of the peripheral nervous system that contains extensive neural circuits capable of local, autonomous function.
For this purpose, we are going to focus on the SNS and PNS solely.
The sympathetic nervous system (SNS) responds more directly to ‘stressed’ thoughts and moods, such as anger, anxiety, worry, frustration, fear, excitement, competition, and sorrow. It produces a stress response to these thoughts and moods.
The parasympathetic nervous system (PNS) responds more directly to “calming” thoughts and moods, such as peace, contentment, confidence, security, and harmony. It helps to calm and relax the body by producing a rest response to these thoughts and moods.
When both the sympathetic and parasympathetic systems are given the opportunity to function normally, they work in opposition to each other to keep the body in balance. When one is active, the other is subdued.
The SNS stimulates the body whereas the PNS calms and relaxes the body.
- The sympathetic nervous system is responsible for stimulating the body.
- The parasympathetic nervous system is responsible for calming and relaxing the body.
- The SNS and PNS work in opposition to each other. When one is active the other is subdued.
The stress response and the General Adaptation Syndrome (GAS)
To enhance our ability to survive and enjoy a long life, the body has a special survival mechanism that engages when we believe we could be in danger. Walter Bradford Cannon, an early 20th-century American physiologist, professor and chairman of the Department of Physiology at Harvard Medical School, called this system the “fight or flight response”. It’s also often referred to as the stress response, the emergency response or the fight, flight, or freeze response (because some people freeze like a “deer caught in headlights” when they feel overly stressed or afraid).
We can think of the stress response as an emergency mechanism the body mobilizes to give us an extra edge or “super-strength” when dangerous situations occur.
Sometimes people have said they felt like they had “superhuman” strength when they were in danger. For example: the ability to lift the full weight of a car because someone was trapped underneath. Or, having the ability to run well beyond a person’s capability in order to get help for someone in trouble. Such feats were made possible by the body’s automatic emergency response system and the hormones it naturally produces when danger is perceived.
In the days when humans had to protect themselves against vicious beasts on a daily basis, this “emergency system” came in handy. Even though the beasts we face today may be different (pressure on the job rather than a Saber-toothed tiger chasing us), the emergency system still responds the same way.
Dr. Hans Selye, a 20th-century Vienna-born scientist well-known for his work on stress and the author of, “The Stress Of Life,” identified three specific stages of the stress response. He called these stages the “General Adaptation Syndrome” (GAS). They are:
- Alarm stage - Sensing danger triggers the stress response. The stress response causes the secretion of stress hormones into the bloodstream where they travel to targeted spots in the body to bring about specific physiological, psychological, and emotional changes that enhance the body’s ability to deal with a threat – to fight or flee.
- Resistance stage – The stress response changes are engaged to give the body an extra “boost” in energy and resources to deal with a threat.
- Exhaustion stage – After the threat has passed, the stress response ends, and the stress hormones are used up or expelled, the body enters a recovery phase where it recovers from the stress response changes and rebuilds its energy stores for next time a stress response is needed.
For simplicity sake, the three stages of an emergency response can be illustrated as:
Notice that when an emergency alarm is triggered, stress hormones flood the bloodstream and instantly cause the many changes that give the body the resources to either fight or flee. As we are fighting or fleeing, the body uses up the emergency resources until the danger has passed. Once the danger has passed, the body comes off of high alert, the SNS gears down, and the body recovers and returns to normal physiology.
Stress hormones affect the body in many ways because they are SUPPOSED to equip the body for emergency action – to either fight or flee.
It’s the thought that counts
Because there is a tight mind/body connection, the moment we “truly believe” we could be in danger, the body produces a stress response as if we are in actual danger. That’s because the brain interprets our thoughts as reality.
The body responds to what we think.
So, the moment you think you could be in danger, your body will produce a stress response whether you are in actual danger or not.
This is why worry – imagining something harmful might happen – can cause stress responses. Again, your body responds to what your mind thinks.
Many anxious people experience stress responses because of something they imagined. In fact, many anxiety (panic) attacks are started because of a thought that frightened them, which triggered a high degree stress response.
For more information about anxiety attacks and how to stop them, see our “Anxiety Attack Symptoms” section.
The Stress Response – How it works
The moment we believe we could be in danger, the stress response activates body-wide changes by stimulating the sympathetic nervous system and suppressing the parasympathetic nervous system. This stimulation and suppression combination rallies the body for emergency action.
Two-phase Stress Response
To accommodate different degrees and lengths of threats, the stress response has two phases.
Phase One - Sympathetic Adrenomedullar System (SAM)
Sympathetic Adrenomedullar System (SAM) provides an immediate physiological, psychological, and emotional adaptation that results in a short-lasting response, such as an increase in alertness, danger surveillance, vigilance, and risk assessment that enables strategic decision-making about the threat.
This initial response to danger is fast but not accurate, meaning the burst of adrenaline is designed to get us out of danger immediately. Once out of danger, then we can think about the threat and decide more appropriate ways of managing it.
For example, the moment we sense danger, the amygdala (often referred to as the fear center of the brain because of its primary role in managing fear) signals the hypothalamus (remember, it’s the “command center” of the brain). The hypothalamus mildly stimulates the sympathetic nervous system, which in turn causes the medulla part of the adrenal glands to release adrenaline and noradrenaline (which are stimulants) into the bloodstream.
Adrenaline (epinephrine) and noradrenaline (norepinephrine) produce a mild form of stimulation with a relatively short duration (a few minutes or so). Like other hormones, their effects are targeted in that they only affect certain parts of the body that have adrenaline and noradrenaline receptor sites, and their effects only last for so long. Overall, these hormones are limited in what they can do and how long they can do it.
For example, adrenaline and noradrenaline stimulate the sympathetic nervous system, which in turn:
- Increases heart rate (noradrenaline increase heart contractions).
- Increases blood pressure.
- Increases oxygen in the lungs by opening the small airways in the lungs.
- Shunts blood from non-vital organs and digestive system to muscles, the brain, and vital organs.
- Dilates pupils.
- Increases sensory perception (senses become heightened).
- Increases blood sugar and fats by releasing them from storage sites in the body.
- Increases the body’s metabolism.
These changes quickly gear the body up for immediate action.
If the threat was only momentary, the stress response would end and the body would enter the exhaustion/recovery phase.
Phase Two – Hypothalamic Pituitary Adrenal axis (HPA)
If the danger is perceived as more threatening or persists for more than a few minutes or so, the amygdala signals the hypothalamus. The hypothalamus releases corticotropin-releasing hormone (CRH). This hormone stimulates the pituitary gland, which causes it to release adrenocorticotropic hormone (ACTH). ACTH stimulates the adrenal cortex, which releases cortisol, the body’s most powerful stress hormone, into the bloodstream.
Cortisol has a more dramatic effect on the body and its effects are longer-lasting. Cortisol elicits a more significant response because its effects are broader and more potent than those of adrenaline and noradrenaline.
Because of how stress hormones stimulate the sympathetic nervous system, which runs throughout the body, the stress response can cause many body-wide changes, including:
Overall stress response body-wide changes:
- Heightens senses (sight, sound, smell, taste, and touch).
- The nervous system goes on high alert.
- The sympathetic nervous system suspends all nonessential bodily functions and increases activity in the areas of the body that are needed to fight or flee.
- Suppresses the immune system and pain response - to help reduce pain and swelling.
- Increases metabolism – so that we have the energy we need to fight or flee.
- Reduces insulin sensitivity.
- Suppresses the production of testosterone.
- Suppresses the growth system – a nonessential system when in danger.
- Increases blood clotting activity - to prevent unstoppable bleeding.
- Interferes with the onset and sustainability of the Sleep mechanism - so that we don’t fall asleep when fighting or fleeing.
Specific stress response body-wide changes:
- Increases activity in the amygdala and hippocampus, and suppresses prefrontal cortex - which heightens fear and memory storage, and reduces executive functions, such as rationalization.
- Increases a sense of danger – caused by the brain function changes above.
- Increases urgency to escape - caused by the brain function changes above.
- Dilates pupils – to take in enhanced visual information.
- Narrows peripheral vision (tunnel vision) - so we can focus on the threat without peripheral distractions.
- Inhibits the lacrimal gland - responsible for tear production and salivation, which helps increase visual perception and reduces digestion.
- Reduces hearing - so that the brain isn’t distracted and overwhelmed by extraneous auditory data.
- Tightens the body's muscles - to make them more resistant to damage, to protect the underlying structures, and to increase reaction time.
- Increases perspiration - to eliminate the body's water through the skin rather than through the kidneys (stopping to urinate when in a dangerous situation may impede or prevent escape).
- Causes goosebumps – Piloerector muscles cause shivers, “goosebumps,” and hair standing on end - to help maintain body temperature (constricted blood vessels and diverted blood cause the surface of the body to cool).
- Increases respiration - breathing increases (shallow and faster breathing) taking in more oxygen and eliminating the body's increased waste products, which are being produced by the increased metabolism.
- Elevates heart rate - to pump the required oxygen and blood sugar-rich blood to the necessary body parts so that the body is ready to take action.
- Increases blood pressure - by contracting the muscular layer in the walls of the arteries to shunt blood away from and to parts of the body more vital to survival, and rushes blood to the muscles.
- Quickly converts the body's storage of sugar (glycogen) and fats into usable energy - for the immediate production of energy at the cellular level.
- Increases blood sugar, oxygen, and blood flow to the brain.
- Inhibits digestion - the body only has so much blood so it shunts blood away from the digestive system and to the skeletal muscles so more of the body’s resources can be used for fighting or fleeing (the body can’t run both large systems at the same time so it diverts blood away from the digestive system to the more important system required for survival). Digestive system inhibition also decreases motility in the digestive tract and increases hydrochloric acid in the stomach to speed food through the digestive system.
- Tightens abdomen muscles - causing an urgency to urinate or void bowels to quickly eliminate any remaining food or waste from the body so that you don’t have to urinate or defecate while fighting or fleeing.
- Pancreas decreases insulin secretion – so that the body’s energy isn’t reduced.
- Kidneys increase renin secretion - a hormone that regulates blood pressure and other physiological functions, such as cell growth and electrolyte balance.
- Relaxes gallbladder.
- Contracts Sphincter muscles.
- Relaxes the bladder - so we don't accidently urinate when we are fighting or fleeing.
- Suppresses sexual arousal.
Even though there are many body-wide stress response changes, they happen quickly – within the blink of an eye. Below is an image that summarizes the stress response and all of the body-wide changes it brings about.
The stress response reaction is proportional to the degree of perceived threat
The degree of stress response alarm is directly proportional to the degree of perceived threat. For instance, believing you are only in minor danger will produce a low degree stress response and resulting physiological, psychological, and emotional changes whereas believing you are in grave danger will produce a high degree stress response and its resulting body-wide changes.
Moreover, the degree of stress response will determine the length of recovery after the stress response has ended. For example, a low degree stress response can be recovered from relatively quickly, such as within a few moments to a few minutes or so. However, a high degree stress response will have a much longer recovery window.
Series of stress responses
Prolonged threats aren’t managed by one big, long stress response. A prolonged threat causes a series of stress responses until the threat has passed. Each stress response in the series will be directly proportional to the degree of threat perceived as the danger unfolds.
For example, every time you think you could be in danger, or think you are still in danger, your body produces a stress response and one that is proportional to degree of danger you believe you are still in. This series of stress responses only stops when you believe the threat has passed and you are no longer in danger.
Rather than one big, long stress response, prolonged threats and stressors produce a series of stress responses.
Once you believe the danger has passed, the length of recovery time is not only proportional to the degree of stress response but also to the length of the series of stress responses. For instance, if a series of low degree stress responses occurred in response to a minor threat over a 15-minute period, recovery might take a few to several minutes. However, if a series of high degree stress responses occurred in response to a major threat over several hours, recovery might take several minutes to an hour or more.
- Stress responses cause many body-wide changes and affect many systems, organs, and glands.
- These changes occur rapidly, within milliseconds of a stress alarm.
- The degree of stress response is proportional to the degree of perceived threat.
- Rather than one big stress response, stress responses occur in a series, and one that is proportional to the length of perceived threat.
- Recovery from the effects of the stress response, or series of stress responses, is proportional to the number and length of stress responses.
- The body needs time to recover from the effects of the stress response so that it can rest and rebuild its energy stores.
When you consider all of the above stress response changes and the degrees to which they occur, it’s little wonder the stress response has a profound effect on the body. It’s also little wonder why the body needs sufficient time to recover from these changes before it can return to normal homeostasis.
If you are interested in more in-depth information about the stress response, we explain it in more detail in the Recovery Support area of our website.
When stress responses occur rarely, the body has sufficient time to recover and rebuild for the next stressful event. But when stress responses occur too frequently, the body doesn’t have sufficient time to recover. Consequently, it can enter into a state of stress-response hyperstimulation since stress hormones are stimulants. See our article “hyperstimulation” for more information about what happens when the body becomes hyperstimulated and how it relates to anxiety symptoms and recovery.
There are no “freebies”
We generally feel the effects of a major stress response as its changes are significant. That’s often not the case with minor stress responses, as their changes can be almost negligible. But, there aren’t any freebies meaning that the body experiences a stress response every time we think we are in danger.
Even though we may not notice the effects of a stress response, the body undergoes stress response changes every time we perceive a threat.
Becoming afraid of the stress response and how it feels
Since the stress response can produce a profound effect on the body, many anxious people become afraid of the sensations associated with the stress response and its physiological, psychological, and emotional changes. For instance:
- An increase in amygdala (fear center) activity and a decrease in cortex (the rationalization area of the brain) activity can make it seem as if the stress response is sinister in itself. Many anxious people become afraid of the feelings of a high degree stress response because of the strong feelings of fear and danger that accompany it. Some people associate these strong feelings with danger itself, and therefore, become afraid of the very response that is designed to protect them.
- An increase in heart rate can also scare people into thinking there is something wrong with their heart when it’s only responding to the stress response the way it is supposed to.
- A stress response can also cause “skipped” heartbeats due to the sudden stimulation of the heart. Some people fear that skipped heartbeats could mean heart trouble when, again, the heart is only responding to the sudden stimulation caused by the stress response.
And so on.
Becoming afraid of the stress response and its many changes is a common catalyst leading to the development of a struggle with anxiety disorder. Recovery Support members can read more about this in chapters 3, 5, 6, and 7.
If you are interested in more information about each anxiety symptoms and its cause, see our “Anxiety disorder signs and symptoms” section.
Can the stress response cause anxiety?
Anxiety is caused by behavior. So, no, stress responses don’t cause anxiety. But they can make threats seem more serious. And, those who are anxious about the stress response and its many changes can become afraid of it or worry about it, both of which create anxiety.
While the stress response doesn’t cause anxiety, being anxious or worried about the stress response does.
You don’t have to be afraid of the stress response, its changes, and how it feels
Even though the stress response can bring about some powerful changes, we don’t have to be afraid of them or how they feel. The stress response is the body’s survival mechanism. It is your friend when in real danger.
Rather than viewing the stress response and its changes as being “bad,” “harmful,” or “dangerous,” you can think of the stress response as being your ally when in dangerous situations and circumstances.
Also consider that many people go to great lengths to create the strong feelings of the stress response, such as skydivers, race car drivers, and other thrill seekers. Those strong feelings of thrill are caused by the very same stress response. The only difference is the attitude about how it feels.
Moreover, cortisol, the body’s most powerful stress hormone, is also our ally when we need energy, especially sustained energy, such as to complete a long task or important project.
Adrenaline “junkies” love the feel of the stress response, and so do those who are passionate about the work they do. Both require a boost of sustained energy.
Also, many people drink caffeinated beverages to keep themselves energized, alert, and clear-headed. The “caffeine buzz” is created by stress hormones - caffeine causes the body to secrete stress hormones into the bloodstream, which is the reason we feel stimulated when we ingest caffeine.
Therefore, we can view the stress response, its changes, and how they feel as our friend and ally rather than something we need to dread. Changing a negative attitude into a positive attitude about the stress response and how it feels can make a significant difference, especially when overcoming anxiety disorder and its symptoms.
The combination of good self-help information and working with an experienced anxiety disorder therapist is the most effective way to address anxiety disorder and its many symptoms. Until the core causes of anxiety are addressed - the underlying factors that motivate apprehensive behavior - a struggle with anxiety disorder can return again and again. Identifying and successfully addressing anxiety's underlying factors is the best way to overcome problematic anxiety.
- For a comprehensive understanding of: Anxiety Disorders Symptoms & Signs, Types, Causes, Diagnosis, and Treatment.
- Anxiety and panic attacks symptoms can be powerful experiences. Find out what they are and how to stop them.
- How to stop an anxiety attack and panic.
- Free online anxiety tests to screen for anxiety. Two minute tests with instant results. Such as:
- Anxiety 101 is a summarized description of anxiety, anxiety disorder, and how to overcome it.
1. Cannon, WB. Organization for physiological homeostasis. Physiol Rev. 1929a;9:399–431.
2. Modell, Harold, et al. “A physiologist's view of homeostasis.” Advances in Physiology Education, Dec. 2015.
3. Weston, Trevor. Know Your Body: The Atlas of Anatomy. "The Nervous System." Berkeley, CA: Ulysses, 1999. N. pag. Print.
4. Bear,Connors, Paradiso (2016). Neuroscience: Exploring the brain - Fourth Edition. Neuroscience: Past, Present, and Future (pp. 13). New York, NY: Wolters Kluwer
5. "THE BRAIN FROM TOP TO BOTTOM." THE BRAIN FROM TOP TO BOTTOM. N.p., n.d. Web. 12 May 2016.
6. ”Central Nervous System.” PubMed Health. N.p., n.d. Web. 12 May 2016.
7. Bear, Connors, Paradiso (2016). Neuroscience: Exploring the brain - Fourth Edition. The Structure of the Nervous System (pp. 179-262). New York, NY: Wolters Kluwer
8. Bear, Connors, Paradiso (2016). Neuroscience: Exploring the brain - Fourth Edition. Chemical Control of the Brain and Behavior (pp. 521-249). New York, NY: Wolters Kluwer
9. Michael Rubin, "Overview of the Peripheral Nervous System." Cornell Medical College, July 2018.
10. Bear, Connors, Paradiso (2016). Neuroscience: Exploring the brain - Fourth Edition. Chemical Control of the Brain and Behavior (p. 533). New York, NY: Wolters Kluwer
11. Biran, Jakob, et al. "Role of developmental factors in hypothalamic function." Frontiers in Neuroanatomy, 21 Apr. 2015.
12. BC Campus. “The Pituitary Gland and Hypothalamus.” Anatomy and Physiology, Rice University, 6 Mar. 2013.
13. Bear, Connors, Paradiso (2016). Neuroscience: Exploring the brain - Fourth Edition. Chemical Control of the Brain and Behavior (pp. 535-536). New York, NY: Wolters Kluwer
14. Feiffer, Ronald. Neurology and Clinical Neuroscience. Neurology Of Gastroenterology And Hepatology, Mosby, 2007, (pp. 1511-1524)
15. McCorry, Laurie Kelly. “Physiology of the Autonomic Nervous System.” American Journal of Pharmaceutical Education, 15, Aug. 2007.
16. Selye, H. Endocrine reactions during stress. Anesthesia & Analgesia. 1956;35:182–193. [PubMed]
17. "Understanding the Stress Response - Harvard Health." Harvard Health. N.p., n.d. Web. 23 May 2016.
18. "Stress." University of Maryland Medical Center. N.p., n.d. Web. 16 May 2016.
19. Selye, H. (1956). The stress of life. New York, NY, US: McGraw-Hill.
20. Godoy, Livea, et al. "A Comprehensive Overview on Stress Neurobiology: Basic Concepts and Clinical Implications." Frontiers In Behavioral Neuroscience, 3, July 2018.
21. Persson, Pontus. “Renin: origin, secretion and synthesis.” The Journal of Physiology, 1 Nov. 2003.
22. Lucassen, Paul J., et al. “Neuropathology of stress.” NCBI PubMed, 8 Dec. 2013.
23. Justice, Nicholas J., et al. “Posttraumatic Stress Disorder-Like Induction Elevates β-Amyloid Levels, Which Directly Activates Corticotropin-Releasing Factor Neurons to Exacerbate Stress Responses.” Journal of Neuroscience, Society for Neuroscience, 11 Feb. 2015.
24. Arnsten, Amy, "Stress signalling pathways that impair prefrontal cortex structure and function." Nature Reviews Neuroscience, June 2009.
25. Romeo, Russell. "The Teenage Brain: The Stress Response and the Adolescent Brain." Current Directory of Psychological Science, Apr. 2013.
26. Diabetes Education Online. "Blood Sugar & Stress." 2019.
anxietycentre.com: Information, support, and coaching/counseling/therapy for problematic anxiety and its sensations and symptoms, including the stress response.