This NBC News Learn video explains what fear is, chemically: a series of responses in the brain and body -- including an increase in heart and respiratory rates, blood pressure, and perspiration -- after release into the bloodstream of two hormones, adrenaline and cortisol, that ready the body for "fight or flight" action.
Chemistry of Fear and Fright
BETH NISSEN, reporting:
It’s a great time of year for fear-of ghosts and ghouls, witches and monsters. What is fear, exactly? Put one way, fear is the emotion, the feeling, of being afraid of some danger or threat, real or imagined. Put another way?
CHRIS BRAUN (Neurobiologist, Hunter College City University of NY): Fear really is just our brain’s experience of our body’s chemistry.
NISSEN: Chemistry that is critical to protecting ourselves from harm. Say you’re in the woods and a grizzly bear rears up and roars. Blink-quick, it happens.
BRAUN: The brain recognizes a situation as potentially life threatening, and initiates a response, starts a bodily response.
NISSEN: Primarily, the release, into the bloodstream, of two groups of hormones: adrenaline, also called epinephrine, and cortisol, sometimes called “the stress hormone, ”both produced by the adrenal glands, a pair of organs that sit atop your kidneys. In a fearful situation, levels of both hormones suddenly increase, and as every teen knows, hormones trigger major changes in living things.
BRAUN: Those hormonal changes prepare the body for danger, of any kind. When those changes occur, the body is primed for action.
NISSEN: Action meaning either fight or flight: stay and maybe wrestle the bear, or back away slowly. (Not a good idea to run from bears. They’re faster than you are. Although once you’re out of the bear’s sight, you might want to run). What’s happening here is kind of a chemical SOS: messages sent by molecules of adrenaline and cortisol throughout the body.
BRAUN: The message to the heart is “beat faster.” Increased pulse rate will prepare the body for either fight or flight. The message to the lungs is to expand the bronchiae – to open the passages of the lungs to get more oxygen into the bloodstream. For the arterioles, the small blood vessels in your body, the message is “constrict” to increase blood pressure. Make the vessels smaller so that the pressure of the fluid within them is higher. The message that the stomach reads is to slow down, to stop the motility, to stop putting energy into digestion. Because that energy will need to be used by the muscles. The message to the muscles takes the form of “use your fuel better.” The increase in cortisol and adrenaline in the bloodstream has very dramatic effects on the muscles, and makes the muscles more effective and stronger.
NISSEN: Effective and strong enough to allow superhuman feats of strength.
BRAUN: The more adrenaline you have, the more these effects will be felt.
NISSEN: Even the skin, or rather, cells just below its surface, gets a message: start sweating.
BRAUN: The increased perspiration is to help your body cool itself in preparation, or in expectation, that it’s going to be working hard, either running or fighting.
NISSEN: And of course, the brain gets messages: Focus! Concentrate! But wait, how is it that the same molecule, adrenaline, can simultaneously send a message to the heart to speed up and the stomach to slow down? Why don’t all these different messages get garbled? Here’s why. The adrenaline molecule is what’s called a stereoisomer. It’s always made up of the same kind and number of atoms, in this case, 9 carbon, 13 hydrogen, 1 nitrogen and 3 oxygen, but can have those atoms in slightly different arrangements – say, ‘mirror’ opposite – and still be the same molecule. Think of it as a key, that works in certain ignitions when it’s fit in like this, or like this. Now think of each of the organs and systems in the body as key-operated machine parts, with specific, highly specialized receptors, or ignition systems. The same adrenaline key fits, in chemistry terms, ‘bonds,’ with these different receptors, signaling the start of a specific process. So the engine of the heart revs up, the machinery of the digestive system powers down, and so on with the other fear responses. It’s like having one key that opens your front door, starts your car, and unlocks your bike: same key, different results. What can trigger a fear response? Almost any of our senses: sight, sound, feel. Or what we think we’re about to see or feel. There’s much more to know about this fascinating and complex psycho physiological response? Afraid we’ve done all we can for now…
PHILADELPHIA — The scenes are too common for comfort: A mother grabs her daughter’s arm roughly on the bus. A father at a convenience store growls coarsely into his son’s ear.
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