A pounding heart, tense muscles and a face drenched with sweat might be what most people picture when they think of someone who is scared. Although these are all physical manifestations of being afraid, there’s a lot going on behind the scenes in the body that make these happen.

The sympathetic nervous system, responsible for the fight-or-flight response, can be activated when a person is in a scary or life-threatening situation. According to Bill Robertson, an assistant professor in the College of Health Professions at Weber State University, this sympathetic nervous system can be activated by a number of different situations.

Robertson said the sympathetic nervous system will heighten the senses of the person who is scared.

“Their eyes may become dilated,” Robertson said. “Their heart will work harder and pump blood faster.”

People whose sympathetic nervous system is activated will also breathe harder in order to supply more oxygen in the body. They may feel their muscles tense up and functions that are non-essential to sustain life, such as digestion, may be shut down.

“Your body doesn’t care about digesting that steak you just ate when you’re in fight-or-flight mode,” said Theresa Kay, who has a Ph.D. in clinical psychology and is an associate professor of psychology at Weber State University.

When in fight or flight mode, the body is more focused on getting blood and oxygen to more important parts of the body, such as the legs or arms, which are used to fight or flee.

According to Kay, the hypothalamus is what starts the flight or flight mode.

“The hypothalamus decides if it’s a threat or not,” Kay said. “If the hypothalamus deems it’s not a threat, then we don’t get fight or flight.”

The activation of this nervous system can come from a wide array of sources. This system played a key role in the development of modern humans, activating when a different tribe approached or a wild animal threatened to attack. It is, to a degree, responsible for our very survival.

Kay says now this nervous system can be activated by something as simple as receiving a warning from a boss or missing an alarm in the morning.

“There’s not that much ability to differentiate between what’s really a threat to our survival and what’s not,” Kay said.

However, if the hypothalamus recognizes a threat, Kay explained that it sends a message to the pituitary gland. Then the pituitary gland then sends a message, in the form of hormones, down to the adrenal glands, which then release adrenaline.

“If you hear about the adrenaline rush happening with scary roller coasters or movies,” Kay said “that’s the system that has been activated.”

Once the sympathetic nervous system is finished, the parasympathetic nervous system, which slows down and stabilizes breathing and heart rate, kicks in. According to Kay, this system is one that helps a person calm down after experiencing the effects of the sympathetic nervous system.

“The systems, in a way, balance each other out,” Kay said.

While the phrase “scared to death” may be popular, especially during Halloween, it is unlikely that an average, healthy person could ever be so frightened that he or she dies.

According to both Kay and Robertson, only those with pre-existing conditions, such as heart or lung problems, are likely to suffer from other health problems following a scare.

Valerie Gooder, an associate professor in the nursing department, said she has never seen even those people reach that point.

“In my 20 years as a nurse in critical care, I’ve never come across someone who was ‘scared to death,'” Gooder said.