2. Distinguish a Stressor from a Stressed Person from a Stress Response

Neuroscience 16c – Stress

Anil Chopra

1.  Define stress

2.  Distinguish a stressor from a stressed person from a stress response

3.  List the main biological features of the stress response

4.  Describe the relationship between stress and general performance

5.  Describe how stress management can improve health & performance

6.  Describe how stress contributes to ill-health

The terminology of stress causes confusion it has 3 meanings:

-  The cause of a problem – i.e. a stressor. It is thought that sources of stress can be clustered into 2 categories

o  Perception – (how we perceive things) that the demand on the patient outstrips their ability to cope with that demand.

o  Communication – how we relate to things and people.

-  The mechanism of stress response. This is a catabolic state that is associated with a negative response. i.e. a problem which creates damage.

-  The effect of the problem caused by persistent stress – e.g. a stress-related disease.

Stress is NOT synonomous with the activation of the sympathetic nervous system and absence of stress is not caused by parasympathetic activation. A biological model for stress was proposed by Prof. James Henry:

The vertical axis represents the autonomic nervous system (ANS):

Top is the sympathetic adrenomedullary (SAM) axis, or sympathetic nervous system (SNS) activation.

Bottom is the parasympathetic nervous system (PNS) activation. Within the ANS there is a third branch not represented in this diagram which is neither SNS nor PNS. The role of this 3rd branch of the ANS in the stress response is unclear.

The horizontal axis represents the neuroendocrine system including the pituitary adrenocortical axis (PAC). The stress response is better clarified as being a catabolic state often associated with activation of the PAC. PAC activation can be associated with either a SNS activation (top right) or PNS activation (bottom right).

Just as it is a mistake to consider SAM activation as synonymous with stress it is an equal mistake to consider parasympathetic activation as the antidote to stress. Relaxation is not necessarily helpful. People who are “relaxed”, with the associated PNS activation and generally a low resting heart rate may still be “stressed”. In the catabolic low arousal state (bottom) right can be the most pernicious of all the four quadrants. There is a widespread misunderstanding that relaxation is by definition a good thing – it is not.

There are a number of catabolic hormones generated by the human system in addition to those generated by the PAC. The main stress hormone is cortisol. Cortisol is most effectively measured in the saliva rather than the blood. It has a circadian rhythm with a peak 30 minutes after waking and a nadir at midnight.

There is still a significant debate as to which measure of cortisol is the best assessment of stress levels. Various authors have suggested that the peak cortisol level during the day is important. Others have suggested that the total cortisol burden throughout the day is important. The general consensus of the field suggests that the morning peak in cortisol is the best measure of overall stress levels.

However, it may be more useful to quantify the cortisol:DHEA ratio. DHEA is the body’s natural antidote to cortisol and one of the key anabolic hormones. In the early days of the stress response both DHEA and cortisol are both synthesised. It is only a little later that pregnenolone (the precursor hormone to both) is channelled into production of cortisol OR DHEA

It has been shown that cortisol: DHEA (Dehydroepiandrosterone) ratio is an indicator of ageing and is high cortisol is attributed to many diseases.

1.  Obesity (cortisol increases fat on the waist)

2.  Diabetes Mellitus (cortisol increases blood sugar)

3.  High Blood Pressure (cortisol disrupts fluid balance)

4.  Heart Disease (cortisol increases cholesterol)

5.  Cancer (cortisol impairs immune function)

6.  Depression (cortisol promotes negative feelings)

7.  Senile dementia (cortisol impairs brain function)

DHEA generally causes anabolism (building of larger molecules) and is generally associated with positive emotions. Cortisol generally increases catabolism, (breakdown of larger molecules) which is associated with depression and negative emotions e.g. depression in Cushing’s Disease. Cortisol is naturally highest at the beginning of the day and this is considered the best measure of cortisol level. It is measured using:

v  PPG, ECG

o  The SDNN is analysed (standard deviation of normal RR)

o  The SDANN is analysed (standard deviation of average RR)

o  The RMSSD is analysed (root mean square successive difference).

o  The pNN50 is analysed (% difference between NN intervals)

o  The ration of high frequency to low frequency heart beats is measured.

o  The circadian rhythm is analysed.

Stress-Performance Curve

Some stress is good for us and some bad. The good stress is “eustress” and can increase up until it gets to the point where it impairs performance – the downslope. Patients with illness often present a “downslope” in their history.