The Body's Response to Stress


The Sympathomedullary Pathway

Immediate (acute) stressors arouse the autonomic nervous system (ANS). It is 'autonomic' because it governs itself. This system is necessary for bodily functions such as your hearbeat - it wouldn't beat properly if we had to think about it.

The ANS is split into two branches; sympathetic nervous system (which gets us ready for fight or flight) and the parasympathetic nervous system (returns the body to a state of relaxation). A key part of this response is the sympathetic adrenal medullary system (SAM); together the SNS and SAM system make up the sympathomedullary pathway.

The Sympathetic Nervous System


  • Sympathetic nervous system prepares the body for action in conditions of immediate (acute) stress; fight or flight - the rapid action necessary when under threat.
  • SNS causes changes such as increase in heart rate and blood pressure, also leads to metabolical changes such as the mobilisation of fat and glucose in the bloodstream.
  • Noradrenaline is the neurotransmitter released by the SNS to activate these internal body organs.
  • SAM system is also activated the same time as the SNS, it releases adrenaline into the bloodstream where it is transported rapidly throughout the body to prepare the animal for fight or flight (this is regulated by the adrenal medulla).
  • Adrenaline boosts the supply of oxygen to the brain and surpresses non-emergency bodily processes such as digestion.
  • PNS stores the body to resting state once the stressor has passed, it slows down the heartbeat and reduces blood pressure. It also restarts digestion. (PNS is often known as the 'rest and digest' system).

The Pituitary-Adrenal System (a.k.a the hypothalamic-pituitary-adrenal axis or HPA)

It is seen as the body's 'stress system'; controlling levels of cortisol (CORT) and other stress-related hormones. Both physical and emotional stressors activate the HPA, however unlike the SAM system, it is much less easy to achieve.


  • Activated under conditions of ongoing (chronic) stress.
  • Activation of the hypothalamus (which happens when stressors are perceived


No comments have yet been made