Fight or Flight

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To produce the fight-or-flight response, the hypothalamus activates two systems: the sympathetic nervous system and the adrenal-cortical system, according to The sympathetic nervous system uses nerve pathways to initiate reactions in the body, and the adrenal-cortical system uses the bloodstream. The combined effects of these two systems are the fight-or-flight response.

When the hypothalamus tells the sympathetic nervous system to activate, the overall effect is that the body speeds up, tenses up and becomes very alert, according to  The sympathetic nervous system sends out impulses to glands and smooth muscles and tells the adrenal medulla to release epinephrine (adrenaline) and norepinephrine (noradrenaline) into the bloodstream. These “stress hormones” cause several changes in the body, including an increase in heart rate and blood pressure.

According to, at the same time, the hypothalamus releases corticotropin-releasing factor (CRF) into the pituitary gland, activating the adrenal-cortical system. The pituitary gland (a major endocrine gland) secretes the hormone ACTH (adrenocorticotropic hormone). ACTH moves through the bloodstream and ultimately arrives at the adrenal cortex, where it activates the release of approximately 30 different hormones that get the body prepared to deal with a threat.

The sudden flood of epinephrine, norepinephrine and dozens of other hormones causes changes in the, stated body that include:

  • heart rate and blood pressure increase
  • pupils dilate to take in as much light as possible
  • veins in skin constrict to send more blood to major muscle groups (responsible for the “chill” sometimes associated with fear — less blood in the skin to keep it warm)
  • blood-glucose level increases
  • muscles tense up, energized by adrenaline and glucose (responsible for goose bumps — when tiny muscles attached to each hair on surface of skin tense up, the hairs are forced upright, pulling skin with them)
  • smooth muscle relaxes in order to allow more oxygen into the lungs
  • nonessential systems (like digestion and immune system) shut down to allow more energy for emergency functions
  • trouble focusing on small tasks (brain is directed to focus only on big picture in order to determine where threat is coming from)

All of these physical responses are intended to help you survive a dangerous situation by preparing you to either run for your life or fight for your life, according to The fight-or-flight response is an instinct that every animal possesses.

“Students especially, may experience flight or flight responses in relation to school based stress, perhaps when walking into a big test you’re worried about or maybe if you have to give a big presentation in front of your classmates,” stated Lisa Lee. “One quick easy way to slow down the fight-flight response is to be aware of your body’s heightened physical response.  Utilizing calming and slow breathing techniques is an easy and accessible way to slow your body down.  Use positive affirmations to combat the irrational thoughts that might creep into your head and recognize that they’re driven by your fear, not reality.

“Your can also work to reduce the likelihood of ever getting into a fight or flight response by working to reduce the stress in your life.  Be good to your mind and body.  Eat nutritious food that help keep your blood sugar in balance.  Try to develop a positive attitude and outlook towards life — Surround yourself with positive people, have healthy relationships, nurture your spirituality. Exercise. Practice mindfulness — Learn yoga, deep breathing, meditation, and try to be present, authentic and more aware of your surroundings.  Yes, this means you should not be texting when enjoying quality time with your friends and family!  And be kind to yourself.  Recognize that your best is different on any given day, and your best is always good enough.”

According to, the process of creating fear takes place in the brain and is entirely unconscious. There are two paths involved in the fear response: The low road is quick and messy, while the high road takes more time and delivers a more precise interpretation of events. Both processes are happening simultaneously.

The idea behind the low road is “take no chances.” If the front door to your home is suddenly knocking against the frame, it could be the wind, according to  It could also be a burglar trying to get in. It’s far less dangerous to assume it’s a burglar and have it turn out to be the wind than to assume it’s the wind and have it turn out to be a burglar. The low road shoots first and asks questions later. The process looks like this:

The door knocking against the door frame is the stimulus. As soon as you hear the sound and see the motion, your brain sends this sensory data to the thalamus. At this point, the thalamus doesn’t know if the signals it’s receiving are signs of danger or not, but since they might be, it forwards the information to the amygdala. The amygdala receives the neural impulses and takes action to protect you: It tells the hypothalamus to initiate the fight-or-flight response that could save your life if what you’re seeing and hearing turns out to be an intruder, according to

The high road is much more thoughtful. Is it a burglar, or is it the wind? The long process looks like this:

When your eyes and ears sense the sound and motion of the door, they relay this information to the thalamus. The thalamus sends this information to the sensory cortex, where it is interpreted for meaning. The sensory cortex determines that there is more than one possible interpretation of the data and passes it along to the hippocampus to establish context. The hippocampus asks questions like, “Have I seen this particular stimulus before? If so, what did it mean that time? What other things are going on that might give me clues as to whether this is a burglar or a wind storm?” The hippocampus might pick up on other data being relayed through the high road, like the tapping of branches against a window, a muffled howling sound outside and the clatter of patio furniture flying about. Taking into account this other information, the hippocampus determines that the door action is most likely the result of wind. It sends a message to the amygdala that there is no danger, and the amygdala in turn tells the hypothalamus to shut off the fight-or-flight response, also according to

The sensory data regarding the door — the stimulus — is following both paths at the same time. But the high road takes longer than the low road. That’s why you have a moment or two of terror before you calm down.

Regardless of which path we’re talking about, all roads lead to the hypothalamus. This portion of the brain controls the ancient survival reaction called the fight-or-flight response, according to