What happen to your body when you fear?

You freeze, your heart feels like it can beat your chest, your legs move, and the hair on the back of your neck stands on end.

It's a common feeling that can be caused by anything from a horror movie to someone coming out and shouting "Boo!" But why does the body react in this way when we are afraid?

In honor of Halloween, we decided to find out.

Anxiety begins with a bullet. When something shocking happens, like someone jumping out of a haunted house, that is a signal to your brain that you may be in danger.

Fear starts in the brain

Most of us do not have to think about breathing, digesting our food, or making our heart beat faster. The autonomic nervous system  is responsible for these activities which we consider to be automatic. It is divided into two branches: the parasympathetic nervous system (the whole digestive and digestive system) and the sympathetic nervous system (the fight or flight system).

Fear kicks your response to a fight or flight into an overdose, Evans said. Your adrenal glands release adrenaline. Blood flow downs to the frontal lobe of your brain, which is responsible for logical thinking and planning, and the deeper, more aggressive parts of your brain - including the amygdala - take over.

Like the animal that tries to avoid being eaten by a hunter, all your body's resources are diverted to one goal: survival. Your heartbeat and blood pressure rise, you breathe faster and your muscles become stronger. Your students stretch to see the threat clearly, Evans said.

Some people may sweat and be drenched or have cold, cold hands when they are scared, he says. That is because blood flows from the extremities of the body to the large, internal muscles.

"If you're going to fight or run away, you want a lot of blood flow to the major muscles of the body," Evans said.

You will also find a decrease in digestive function. Peristalsis, which is a movement similar to the flow of systems in the intestine that controls digestion, takes a lot of energy, Evans said. And your body has no time for that when you try to avoid joining the Army of the Dead.


"All that we think of as long-term interests are diverted to the immediate passion: fighting or flying," he said.

The combat or flight system was useful to the first humans, who were always confronted with giant beasts (and alone), but modern society has little need these days. In fact, the answer to a fight or a plane may be dangerous in modern times: We now live in the old age that fear can cause heart disease, says neuroscientist Martin Samuels told Scientific American.


Our bodies can change the response to fear very quickly, however. When it turns out that we are not in a life-threatening condition, the parasympathetic nervous system (PSNS) intervenes in the fight against the urge to fight, or in particular, by stopping the adrenaline rush and lowering our heart rate to normal.

That’s why every time we jump in during a horror movie we don’t stop at the theater screaming; after the initial response, our PSNS helps us to see that the threat is not real and makes us calm down.

Part of the reason why PSNS exists is because adrenaline can be very dangerous. If adrenaline gets too high, it can lead to organ failure and death, emergency physician Rober Glatter told Live Science.


And it’s not just a dangerous fear: Any extreme feeling can trigger an adrenaline rush. You can't manually prevent a war-or-flight response from happening, but things like meditation can help you stay calm the next time you fight fear or other powerful emotions, Glatter told Live Science.