Brain and Body Response to Fear

What is Fear?

Fear: Distressing negative emotion induced by a perceived threat basic survival mechanism.

Most people usually fear future events

A response to a specific stimulus, such as pain or the threat of danger

Fear is the ability to recognize danger and flee from or confront it

Fear should be distinguished from the related emotional state of anxiety, which typically occurs without any external threat.

Fear is related to specific behaviors of escape and avoidance

Anxiety:the result of threats which are perceived to be uncontrollable or unavoidable

External Fear: caused by something outside of you which you are strongly motivated to avoid

                        Ex: Fear of spiders

Internal Fear: something inside of you that you link a negative emotion to

                        Ex: Fear developed out of low self-esteem

Parts of the Brain

Thalamus - decides where to send incoming sensory data (from eyes, ears, mouth, skin)

Sensory cortex - interprets sensory data

Hippocampus - stores and retrieves conscious memories; processes sets of stimuli to establish context

Amygdala - decodes emotions; determines possible threat; stores fear memories

Hypothalamus - activates "fight or flight" response

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The Two Roads of Fear

Low Road

    Brain reacts quickly no matter what the situation

Door smacks against door frame-could be wind or could be burglar—the low road takes no chances and assumes that the sound was a burglar breaking in because it is less dangerous to assume the worst than assume nothing.

High Road

    Brain reacts slowly

    The brain analyzes the situation before acting.


Hypothalamus activates two systems

·         Sympathetic Nervous System

·         Adrenal-cortical System

Sympathetic nervous System

·         Uses nerve pathways to initiate reactions in the body

·         The sympathetic nervous system sends out impulses to glands and smooth muscles and tells the adrenal medulla to release epinephrine (adrenaline) and nor epinephrine (noradrenalin) into the bloodstream.

Adrenal-cortical System

·         Uses the bloodstream to initiate reactions in the body

·         Activated by the release of corticotrophin-releasing factor

·         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.


Once the two systems activate, the body:

·         Speeds up

·         Tenses up

·         Becomes alert


The sudden flood of epinephrine, nor epinephrine and dozens of other hormones causes changes in the 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)

Fight or Flight Response

Common Fears

1. Terrorist attacks
2. Spiders
3. Death
4. Failure
5. War
6. Heights
7. Crime/Violence
8. Being alone
9. The future
10. Nuclear war