The Fight or Flight Response (AQA AS Psychology)

The fight or flight response

• During situations that produce stress, fear or excitement, the neurons of the sympathetic nervous system stimulate the adrenal medulla (of the adrenal gland) to secrete adrenaline

• Adrenaline is a hormone that prepares the body to deal with a fear/stress/excitement-inducing stimulus, e.g.

  • walking home at night and hearing footsteps following closely behind

  • preparing to go onstage and perform in a play or concert

  • waiting outside an office for an interview

Effects of adrenaline

• The heightened reaction produced by adrenaline is known as the ‘fight or flight’ response i.e. stay and face the danger or run away quickly!

• When a ‘danger’ signal is detected by the senses the following mechanisms are triggered:

  • The adrenal glands also release adenosine triphosphate (ATP), an energy-storing molecule that provides a short-lived, intense surge of power, designed to move someone quickly out of danger’s way

  • Adrenaline is transported around the body in the bloodstream and binds to receptors on its target organs

  • One of the targets of adrenaline is the SAN, leading to an increase in the frequency of excitations

    • There is an increase in the heart rate to supply blood to the muscle cells at a faster rate

    • More blood means more oxygen and glucose available for muscle cells, which in turn, increases the rate of aerobic respiration

    • More energy is therefore provided to deal with the situation

  • Adrenaline also stimulates the cardiovascular control centre in the medulla oblongata

    • This action increases the impulses travelling along the sympathetic neurons affecting the heart, further speeding up the heart rate

  • Blood vessels to less important organs (such as the digestive system and skin) constrict so that more blood can be diverted to organs that will be involved in the "fight or flight" response

    • Blood flow to the brain remains constant, regardless of whether the body is in a state of stress or relaxation

    • The brain is one of the most important organs in the body and needs a constant blood supply to function properly

• Physiological changes brought about by the fight or flight response include:

  • increased heart rate

  • dry mouth

  • increased sweating

  • dilated pupils

  • increased breathing rate

• Once the threat/danger has passed it is possible that someone may feel exhausted, sick or ravenously hungry due to the energy that has been released during the response

  • If this energy is not used via exercise/action then it can ‘sit’ in the body, possibly leading to stress and other long-term health conditions e.g. someone with high anxiety is probably living in a constant state of fight or flight