The flight or fight response- responses to acute and chronic stress

What makes up the response to acute (stress)?

Response to acute (sudden) stress:

Sympathetic nervous system→ noradrenaline→ parasympathetic nervous system

What does the sympathetic nervous system do in response to acute stress?

In the sympathetic nervous system,

• when the SNS is triggered, it begins preparing the body for fight or flight

• the SNS sends a signal to the adrenal medulla, which releases noradrenaline into the bloodstream

What does noradrenaline do in the response to acute stress?

• noradrenaline cirulates in the body, causing physiological changes

• the heart beats faster, more blood to the muscles, heart and other vital organs

• blood pressure increases

• breathing becomes rapid, increasing oxygen uptake

• noradrenaline also triggers the release of glucose and fats, into the bloodstream, supplying energy to parts of the body associated with fight or flight

What does the Parasympathetic nervous sysem do in response to acute stress?

In the parasympathetic nervous system,

• when the threat passes, the parasympathetic branch dampens down the stress response

• heart rate slows down again and reduces blood pressure

• digestion begins again after the SNS has inhibited

What makes up the response to chronic (ongoing) stress?

Response to chronic (ongoing) stress=

• if the brain continues to perceive something as threatening the second system kicks in

• as the initial surge of noradrenaline subsides, the hypothalamus activates a stress response system called the HPA axis (hypothalamus, pituitary and adrenal glands)

What happens to the hypothalamus in the HPA axis?

• in response to continued threat, the hypothalamus releases a chemical messenger, corticotrophin-releasing hormone (CRH), which is released into the bloodstream in response to the stressor

What happens to the pituitary gland in the HPA axis?

• CRH causes the pituitary gland to produce and release ACTH

• ACTH is transported in the bloodstream to its target site in the adrenal glands

What happens to the adrenal glands in the HPA axis?

• ACTH stimulates the adrenal cortex to release stress related hormones, including adrenaline and cortisol

• cortisol is responsible for several effects that are important in the fight or flight response

  • +ve effects- quick burst of energy and lower pain sensitivity

  • -ve effects- impaired cognitive performance and lowered immune system

Who suggested the ‘tend and befriend’ response?

Taylor et al suggested the ‘tend and befriend’ response.

What is the ‘tend and befriend’ response?

For women, behavioural responses to stress are more characterised by a pattern of tend and befriend than fight or flight. This involves protecting themselves and their young through nurturing behaviours (tending) and forming protective alliances with other women (befriending).

Women may have a different system for coping with stress because their responses evolved in the context of being the primary caregiver of their children. Fleeing at any sign of danger would put a female’s offspring at risk. This finding, explained in terms of the higher levels of the hormone oxytocin in females, suggests that previous research, which has mainly focused on males, has obscured patterns of stress response in females.

What are the negative consequences of the fight or flight response?

Negative consequences of the fight or flight response=

The physiological responses associated with fight or flight may be adaptive for a stress response that requires energetic behavioural responses. However, the stressors of modern life rarely require such levels of physical activity. The problem for modern humans arises when the stress response is repeatedly activated.

For example, the increased blood pressure that is characteristic of SNS activation can lead to physical damage in blood vessels and eventually to heart disease. As a consequence, although cortisol may assist the body in fighting a viral infection, too much cortisol suppresses the immune response, shutting down the very process that fights infection and increasing the likelihood of stress-related illness.