Science Mumbo Jumbo part I

* This is a long post on the science behind the claims I have made recently about methods for preventing and healing from chronic stress. If you like science, read on! If not, I won’t be offended if you pass on this one.

Does it ever seem like pop psychology advice is not particularly helpful? Like maybe it’s just smoke and mirrors and not-so-scientific wishful thinking? Consider these self-help book titles: “4 Steps to self-actualization and becoming the best version of you.” “My journey into life’s perfection.” “Stop beating yourself up and leave insecurity behind.” “A guide to the consciousness of man’s self in a transitioning time.” Transitioning… what? Sounds like a bunch of psychobabble to me.

If you’re anything like me, then you are skeptical of the mental and physical health claims made by TV personalities or written in books and blogs (like this one!). Who are these people, anyway? Do they have anything to gain by convincing me, like selling a product or promoting an agenda? No, if you’re careful, then you want to see the proof behind the claims.

As a scientist, I have access to research articles written by qualified, unbiased psychologists and neurobiologists (you have access too if you know where to find them and how to read them). These articles have been vetted through anonymous peer reviewers and meticulous editors. I can attest to the fact that it is remarkably difficult to get research published in these professional journals; only the very best work passes muster and makes it to publication.

I’ve spent the past several months investigating different stress prevention and recovery methods by poring through the psychology research journals. Here is an explanation of some of the more useful findings.

  1. How does the human brain process stress? And why does it sometimes make us physically sick?

It all begins with the limbic system, sometimes called the emotional brain. It is largely involved in processing memory and emotion information it receives from other parts of the central nervous system. The limbic system is composed primarily of two parts of the brain called the amygdala and the hippocampus. The amygdala processes external information related to danger and coordinates a fear response. The hippocampus, on the other hand, is mainly responsible for forming and retrieving both long- and short-term memories, important in interpreting future situations. Together, their job is (in part) to stimulate the hypothalamus, which links the central nervous system with the rest of the body via hormones and electrical impulses.

The HPA axis, responsible for the stress response, is located just above the brain stem.

The HPA axis, responsible for the stress response, is located just above the brain stem.

The amygdala and the hippocampus process data from the current situation in light of emotions, feelings, and memories. In the case of a potentially stressful situation, its job is to decide the level of a threat. It’s important to point out here that the limbic system cannot distinguish perceived threat from actual threat. Thus, our perception of a situation, including our emotional sensitivity and the way we remember past events, plays a huge part in determining whether our brains initiate a full-body response to a situation. In other words, our feelings and memories directly impact how stress affects us.

If the limbic system is convinced that a threat is real and needs a response from the sympathetic nervous system (think fight-or-flight), it stimulates a cascade of events beginning with the hypothalamus. Remember, the purpose of the hypothalamus is to connect the brain to the body (and other parts of the central nervous system). It communicates to the body via autonomic nerves (the involuntary nervous system) and hormones (the endocrine system). The endocrine system is a complex set of organs and glands throughout the body that create hormones (body signaling molecules) telling the body what the brain wants done. Thus, the hypothalamus connects our mental self to our physical self via neurotransmitters (nerve signaling molecules) and hormones.

The hypothalamus has a strong influence over the involuntary functioning of our abdominal organs, especially the circulatory and digestive systems. The same brain structure, then, that is involved in interpreting stressors (from the limbic system) also has sway over our heart and gut functions. When the lines cross in the hypothalamus and our emotions have a physical effect on our heart and gut health, we call it a psychosomatic illness.

Limbic --> hypothalamus -->  pituitary --> adrenal --> body

Limbic –> hypothalamus –> pituitary –> adrenal –> body

How exactly does the hypothalamus accomplish this amazing feat? You guessed it, more hormones. The hypothalamus secretes, among other things, a signaling molecule called corticotropin-releasing hormone (CRH). In the short term, CRH itself causes suppressed appetite, increased anxiety, and increased mental focus. CRH is also responsible for decreasing movement of food (motility) in the stomach and small intestine (loss of appetite, butterflies in the stomach, possible vomiting) while increasing motility in the large intestine (diarrhea, gas, bloating). It also plays a very important role in the symptoms of stress and anxiety by stimulating what’s known as the hypothalamus-pituitary-adrenal (HPA) axis. By the action of one hormone, CRH, two endocrine glands (pituitary and adrenal) are now activated. But what do they do?

This quickly growing pool of CRH causes the pituitary gland to secrete adrenocorticotropic hormone (ACTH), which stimulates the adrenal gland to produce cortisol.

Still with me?

When we are not under noteworthy stress, cortisol levels follow a circadian rhythm, peaking in the early morning hours (waking up can be stressful!) and decreasing throughout the day to its lowest point at bedtime. (For proper cortisol functioning, it is important to have a regular cycle of sleep and wake times). It is also produced during exercise. In both of these circumstances, it is helpful for managing the minor stressors we encounter every day.

Cortisol has far-reaching effects on the mind and body during stress. Its purpose is believed to be preparation for fight-or-flight, survival in the face of real danger. In the short term, cortisol increases blood sugar as well as the metabolism of fat, protein, and carbs, all likely in an effort to have ready stores of energy on hand for the fight (or the flight). Cortisol is also immunosuppressive, leaving us more susceptible to infection during times of extended or repeated stress. And gastric acids are increased by cortisol, possibly accounting for the common connection between stress and heartburn. Importantly, cortisol also alters cardiac and gastrointestinal functions, which we will come back to.

In addition to cortisol, the adrenal gland also secretes its namesake, adrenaline, more commonly referred to as epinephrine. But rather than responding to ATCH, epinephrine is produced in response to neurotransmitters from the sympathetic nervous system.

Epinephrine has a partner called norepinephrine. I’ll lump them together here for simplicity, referring to them both as epinephrine. Produced by the adrenal gland in response to direct nerve impulses from the hypothalamus and other brain regions, epinephrine is very important in the stress response. It stimulates the liver to release glucose into the blood stream, decreases hunger and digestive activity, dilates the bronchioles of the lungs, and increases our heart rate and blood pressure (all presumably to improve transport of glucose and oxygen to muscle cells).

Cortisol and epinephrine are essential to the fight-or-flight response.

Cortisol and epinephrine are essential to the fight-or-flight response.

Epinephrine further stimulates the sympathetic nervous system, a part of the brain and spinal cord that is intended to provide a rapid, short-term response to threatening situations. Mental alertness and arousal and generation of chemical energy are the hallmarks of the sympathetic response. Blood flow to the gastrointestinal tract is also decreased, leading to malnutrition and weight loss if the response is not reversed (i.e., if the stress is chronic).

If we are in a place of emotional sensitivity (chronic stress, depression, fear, loss of a loved one, etc.), epinephrine is a primary cause of anxiety. If the parasympathetic nervous system, whose job it is to reverse the sympathetic response, is not allowed to restore homeostasis, epinephrine can cause headaches, body tremors, and even panic attacks.

What exactly are the parasympathetic and sympathetic nervous systems? These two systems reside in different parts of the central nervous system and control our involuntary, or autonomic, processes. The parasympathetic nervous system maintains energy use as low as possible, keeping you calm and your various involuntary functions moving smoothly. The sympathetic nervous system, by contrast, tries to ramp up all of our activities. Most of our abdominal organs have dual innervation, meaning that they are connected to both parasympathetic and sympathetic nerves. The result is generally a dynamic antagonism where neither dominates and we are kept calm and low-energy but ready to jump into action if necessary.

Our response to psychological stress can be identical to our response to a life-threatening situation.

Our response to psychological stress can be identical to our response to a life-threatening situation.

The parasympathetic nervous system exists in the central nervous system at the brain and the lower spinal cord. It mainly uses a neurotransmitter called acetylcholine to keep digestion, defecation (pooping), and diuresis (peeing) on track. It also keeps your breathing slow and your overall disposition calm.

The sympathetic nervous system, which exists in the middle of the spinal cord, responds to nerve impulses from the hypothalamus in the brain to send epinephrine directly to specific organs to ramp things up (epinephrine can be produced by both the adrenal gland and sympathetic nerves). It can increase blood glucose levels by communicating with the liver, cause muscles to tense up leading to shaking and twitching, and increase the metabolic rate of target cells.

One final piece is the vagus nerve, a predominantly parasympathetic structure that runs between the brain and organs in the chest and gut (heart, lungs, and digestive organs). Signaling traffic in the vagus nerve is two-way, receiving data from the chest and gut and sending data back to it from the brain. It is believed that signals from the vagus nerve reach the brain and alter everything from digestive processes and heart and breathing rates to emotions and decision-making. In fact, the gut has an entire nervous system of its own called the enteric nervous system.

It turns out that the digestive tract is controlled by both the central nervous system and a separate, gigantic nervous system called the enteric nervous system. The ENS has over 100 million neurons, more than the spinal cord. It controls gut motility (movement of food and feces through the tract) and secretion of mucus and other digestive liquids. The central nervous system, for its part, sends sympathetic and parasympathetic signals to the gut. The parasympathetic signals increase motility and secretion while the sympathetic nerves decrease these activities.

When stress causes constipation, it is the sympathetic nerves bringing movement to a halt. But more commonly, stress causes too much liquid and too much movement in the intestines. This is believed to be due to the parasympathetic system overcompensating for the sympathetic’s flight-or-flight response.


About Dave Cummings

Dave Cummings is a husband, father of three, college professor, biologist, and urban outdoorsman. Most importantly, he is a Christ follower.
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6 Responses to Science Mumbo Jumbo part I

  1. Vickie Rowlett says:

    Good info. Reminded me of some of the material talked about in classes I took this summer. Thanks Dave!

  2. paherrington says:

    Well done professor! …written in a way that the non-scientific nervous system could understand it. I’ve never heard it explained this clearly. I’d love to explore more about how exercise connects with stress release (and how it might help mitigate migraine headaches!)

    • Thanks Phil. Understandable was my goal. I’ve got another one coming, explaining what’s known about exercise and a couple other “interventions”. I’ll see what I can dig up on migraines (I get them too).

  3. Loren E says:

    Great info, Dave!

    Let me clarify and connect some dots.

    “1. How does the human brain process stress? And why does it sometimes make us physically sick?”

    So how do you define stress? Is stress simply anything that makes our body react like this?

    From what you are saying, it seems that our individual reaction is key; if someone reacts physically to mild events, it’s still something we call stress. And conversely if someone doesn’t react physically to a severe event, then we’d say they didn’t have stress.

    The reason I’m asking is that it points towards a remedy. On the one hand, if stress is the event or circumstance itself; the solution might be to get rid of these sort of events. But if stress is our response, the answer might be to learn to react better so these events are no longer stressful. I could quit my job for a less stressful job, or I can learn to cope with a work environment that could be stressful if I let it be.

    • That’s an important clarification, Loren. Technically, a stressor is anything that challenges the status quo, our equilibrium. Stress, then, is our physical and mental reaction to a stressor. Not all stress is bad. Stress challenges us to grow, to learn, and to be creative. Good stress is called eustress (like Euhus, but with stress). Bad stress is called distress. We learn from and grow from eustress. It brings out the best in us. Distress, on the other hand, leads to anxiety (what we often call being stressed out) or depression. Distress is stress that we cannot learn or grow from. You are absolutely right that our response to stressors and stress is key to our mental health. Chronic stress (work, home, budget, etc.), poor diet, lack of exercise, or a generally negative outlook on life can result in distress as our response to stressors. We can learn, as you said, to process stressors in a way that does not lead to a distress reaction but instead a eustress (or at least stress-neutral) response. We are not victims in our response – we have many options for how we respond to the inevitable challenges of life.

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