Fight or Flight Response
Psychology: AQA A Level, topic 6.1.5
The Fight or Flight Response
The fight or flight response is an adaptation that helps us to survive when we face a threat. The response is mainly due to the sympathetic nervous system and the hormone adrenaline.
A survival mechanism
- The sympathetic nervous system is activated when we are faced with stressful or high-arousal situations.
- The activity of this system was adaptive for our ancestors and increased their chances of survival.
- Imagine, for example, that one of our early ancestors suddenly disturbs a large bear with her cubs while out hunting.
- At that moment, his body undergoes a series of changes - a direct function of sympathetic activation - preparing him to face the threat.
Changes in the body
- When the fight or flight response is activated, many changes occur.
- Pupils dilate, heart rate and blood pressure increase, the bladder relaxes, the liver releases glucose, and adrenaline surges into the bloodstream.
- This series of physiological changes allows the body to access energy reserves and heightened sensory capacity so that it might fight off a threat or run away to safety.
After the threat
- Once the threat has been resolved, the parasympathetic nervous system takes over and returns bodily functions to a relaxed state.
- Heart rate and blood pressure return to normal, pupils constrict, control of the bladder is regained, and the liver begins to store glucose in the form of glycogen for future use.
- These processes happen when the parasympathetic nervous system is activated.
Stress and the sympathetic nervous system
- The physiological mechanisms of stress are very complex, but they generally involve the work of two systems - the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis.
- When a person first perceives something as stressful, the sympathetic nervous system triggers arousal via the release of adrenaline from the adrenal glands.
- Releasing these hormones activates the fight-or-flight responses to stress, such as accelerated heart rate and respiration.
The HPA axis
- At the same time as the sympathetic nervous system becomes active, the HPA axis, which is mainly endocrine in nature, becomes especially active.
- It works much more slowly than the sympathetic nervous system though.
- In response to stress, the hypothalamus (one of the limbic structures in the brain) releases corticotrophin-releasing factor, a hormone that causes the pituitary gland to release adrenocorticotropic hormone (ACTH).
Stress hormones
- ACTH activates the adrenal glands to secrete a number of hormones into the bloodstream. An important hormone is cortisol, which can affect almost every organ within the body.
- Cortisol is commonly known as a stress hormone. It helps provide that boost of energy when we first encounter a stressor, preparing us to run away or fight.
- But sustained elevated levels of cortisol weaken the immune system.
Test yourself on Fight or Flight Response
Which of the following are changes that occur during the fight or flight response?
The HPA Axis Stress Response
What is the main negative effect of cortisol?