The fight-or-flight response is designed to prepare us for danger, but what really happens, when the adrenaline kicks in?

On a bright sunny morning, you are walking down the street, minding your own business, when suddenly you come face-to-face with a hungry lion. Your heart starts pounding; your mind fires to attention.  It’s the biological equivalent of revving an engine: From one moment to the next, your muscles are energized. Lights and sounds are sharper. Your memory is crystal clear. And if you were to get scratched, you wouldn’t feel pain. In that moment, you’re Superhuman.

We have all heard stories (some true, many embellished) about ordinary people performing extraordinary feats in the heat of the moment: panicked mothers lifting cars off their trapped babies, campers fighting off bears to save their loved ones. What’s going on?

Fight or flight

You may feel that emotions just get in the way, but you would be wrong. Our emotions evolved as a way to send us powerful signals that are not easy to ignore. And that can be a good thing. Without fear, for example, that lion would be downright dangerous.

The American physiologist Walter B. Cannon coined the term fight-or-flight back in 1915 to describe an animal’s ability to mobilize an emergency response with a “violent display of energy” in his ground-breaking book Bodily Changes in Pain, Hunger, Fear and Rage. 

The main way your brain is able to communicate with the rest if your body is to send messages through the billions of neurons that branch down your spine and out to your limbs. Conscious decisions, like lifting your arm or writing an email, are performed by the voluntary nervous system.

But there are also largely unconscious decisions like blushing or digesting that are covered by the autonomic nervous system. It branches to two main tracks: “rest and digest” (the parasympathetic nervous system) and “fight-or-flight” (the sympathetic nervous system).

fight or flight
The term “fight or flight” was coined by psychologist Walter B. Cannon in 1915 and describes a “violent display of energy” which an animal mobilizes as an emergency response. Animals are only human too, right? // © Shutterstock

 

As every first-year medical student learns, the sympathetic nervous system mediates the 4Fs of behavior — flight, fight, fright and f… well, sex. Nerves involved in fight-or-flight branch out to nearly every organ, blood vessel and sweat gland in your body.  It reacts to what your body perceives as emergencies by releasing several neurotransmitters, most famously adrenaline (also known as epinephrine to Americans).

The name thus remains a source of serious trans–Atlantic confusion. Both words mean “on top of the kidneys,” it’s just that the Americans chose a Greek root and the British a Latin one. Also no one really wants to call it dihydroxyphenol methylaminoethanol.

As the name implies, your adrenal glands are indeed nestled right above your kidneys, weighing only a few grams each. They are responsible (among other things) for most of the adrenaline that is circulating in the body.

Adrenaline is able to work within seconds. It increases blood flow and oxygen supply to your muscles. It causes your heart to work harder, dilates your pupils and increases your blood sugar. At the same time, your body changes its priorities. Long-term high-energy projects like growth, reproduction and monitoring your immune system are put on hold. Pain perception is blunted (if you are injured, you still need to be able to run away) and certain aspects of memory improve (remembering a good hiding place nearby can be quite useful).

Its fast-acting effect on blood vessels is one of the reasons that an adrenaline shot is such an effective drug for anaphylaxis, a life-threatening, rapid onset allergic reaction. Adrenaline can quickly constrict blood vessels to increase blood pressure, improve breathing by relaxing the smooth muscle in the lungs, and reduce swelling.

Despite what you may have learned from Pulp Fiction, adrenaline is normally injected into the veins, not the heart to counteract a heroin overdose. And doctors are more likely to use a drug called “naloxone,” which today can be given as a nasal spray.

From lions to in-laws

Unless currently on safari, most of us are more likely to face a job interview or our future in-laws than a lion.

This is important, because while our fight-or-flight response is designed to prepare us for very real dangers, it often overreacts. Think of it as a smoke alarm that doesn’t know the difference between a burning pizza or a house fire. Only one is really dangerous, but the result is the same: a wailing alarm that is hard to ignore.

In Why zebras don’t get ulcers, Robert Sapolsky describes how sustained psychological stress kicks in our fight-or-flight responses far too often and can indirectly be making us sick.

For most animals, stress is a clear, short-term crisis, as in our lion example. Sustained psychological stress, evolutionarily speaking, is relatively new for humans. We might worry for months or years on end about work, relationships or debt. The problem is that whether we are being chased by a lion or going on a job interview the physiological reactions are the same. Our stress response still triggers our muscles to work like crazy to save our skin.

Austrian-Canadian endocrinologist Hans Selye, first identified the negative effects of stress response on health in the 1930s when his laboratory rats developed consistent symptoms – peptic ulcers, enlarged adrenal glands and a worn-down immune system – from exposure to long-term stress. It was a classic story of learning from error: The rats were stressed out because Selye accidently kept dropping them and then needed to chase them around the lab.

So responding with an adrenaline rush in the face of a hungry lion is fine, but reacting every time someone gets on your nerves could be increasing your risk for cardiovascular disease.

Harnessing your inner superhero

Triggering your fight-or-flight response too often may make you sick, but for adrenaline junkies out there, you can still stimulate safe levels of adrenaline with regular exercise. Go for a quick run or a swim and you will be kicking your adrenaline blood levels into gear.

And for a moment you might also feel just a bit superhuman.