At some point in life, we all feel panic — that gripping, mind-numbing terror over a perceived threat. For some, it’s in response to a situation that holds the potential for actual harm — like say, when a car swerves in one’s direction. For others, it’s in response to a situation that holds little potential for actual harm, but involves, say, rodents of unusual size (read: literally all rodents) or audiences. And for still others — some panic disorder sufferers — it could be in response to really nothing at all except the possibility of a panic attack. But regardless of cause, the physical, panicky experience is the same because what happens in the body during panic is the same; the biology of panic follows the same basic flow, involving nearly every organ system of the body in our response to extreme fear.

The nervous system’s response to panic

Panic starts with the nervous system — with our eyes and ears, typically, which allow us to sense our perceived threat. The sensation passes through the nerves that connect these organs to our brain’s limbic system, particularly the amygdala, which registers the sensation as a threat and begins coordinating the body’s ‘fight-or-flight’ response, according to a 2017 Smithsonian magazine article.

At this point, a few things happen. Our senses become heightened, particularly our vision, as our brain kicks into high alert and forces us to zoom in our focus on the perceived threat; it sidelines all other smaller worries, thoughts, and concerns. Our pupils actually expand to take in more visual information and to better track fast-moving objects, according to the BBC’s Science Focus.

At the same time, our limbic system is going into hyperdrive, its counterpart, the prefrontal cortex, is trying to analyze context and make sense of the threat, according to Smithsonian magazine. (Part of the limbic system, the hypothalamus, is also involved in this.) If the threat is not real, the prefrontal cortex can dial back the limbic system’s fear response. If the threat is real, however, the prefrontal cortex may become overwhelmed by the limbic system — with potentially embarrassing results (see below).

The endocrine system’s response to panic

In response to the amygdala’s signals, the endocrine kicks into action. The adrenal glands start secreting the energizing stress hormones, adrenaline and cortisol. The hypothalamus and pituitary gland start releasing feel-good endorphins, such as dopamine, which dull our perception of pain, in anticipation of injury. These are responsible for the “rush” or the falsely named “adrenaline high” some people experience in scary situations, according to a 2014 Women’s Health article.

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The circulatory system’s response to panic

Meanwhile, our heart rate quickens and our blood vessels narrow in an effort to divert blood supply away from our core to extremities like our legs, which are important in helping us run away if needed. As a result of forcing blood through narrower openings at a quicker rate, our blood pressure rises — which can cause a pounding feeling in the head or chest and/or prompt feelings of lightheadedness or dizziness, according to the Texas Heart Institute. Sometimes, blood pressure drops sharply, which can have similar effects, including faintness. Experts suggest this panic response developed evolutionarily to help us “play dead,” according to the Women’s Health article.

The skeletal system’s response to panic

A recent discovery suggests our bones might be at the figurative heart of panic, maybe even playing a bigger role than adrenal glands in our flight-or-flight response. In response to threat, our bones secrete a hormone known as osteocalcin. Researchers who discovered that osteocalcin plays a role in panic theorize that the hormone might, in fact, play the leading role, triggering the amygdala’s response, which then triggers all other responses and hormones. In an experiment, rats that were genetically modified not to respond to the release of osteocalcin showed slower and duller fight-or-flight responses, according to a recent report in Gizmodo. By contrast, rats whose adrenal glands had been removed were still able to immediately panic.

The digestive system’s response to panic

As blood is diverted away from core organs, digestion slows, according to the Smithsonian article. This can prompt a nauseous or pit-of-the-stomach feeling.

The respiratory system’s response to panic

The bronchi, the tubes that connect the lungs to the windpipe, dilate to take in as much oxygen as possible. For the same reason, breathing rate increases. But this may lead to over-breathing, or, hyperventilation — rapid, shallow breathing that leaves one feeling short of breath, smothered, or suffocated. Hyperventilation can cause a sharp drop in the level of carbon dioxide in the blood, as blood floods with excess oxygen. This can also cause feelings of faintness, dizziness, and lightheadedness, as well as dry mouth, numbness, or tingling, according to VeryWellMind.

The muscular system’s response to panic

Blood floods through the skeletal muscles — the muscles responsible for movement — with glucose, per the Smithsonian article. Glucose is the main ingredient of ATP, which is essentially muscle fuel. All muscle cells store a little ATP in them, but only enough for three seconds of activity. The increase in glucose allows the muscles to start churning out ATP in case one needs to run away fast or fend off an attack. If there is nothing to flee or fight, the overprepared muscles may start trembling, according to the BBC’s Science Focus.

Incidentally, for diabetics, this sharp increase in blood glucose levels may be a problem; a 2006 study found diabetics who experienced panic attacks also experienced increased diabetic symptoms and complications and overall poor self-rated health.

The exocrine system’s response to panic

Panic prompts sweating, as the body cools itself in preparation for a burst of activity, according to the BBC’s Science Focus.

The renal system’s response to panic

Finally, the body may suddenly relieve itself of waste — i.e. panic can literally make us pee our pants — because the limbic system of the brain, which coordinates our fight-or-flight response, overwhelms our prefrontal cortex, the part of the brain that (among other things) can inhibit the urge to pee, according to a 2011 explainer by Slate.