in this summary you will read about stress: what the consequences of long term and short term stress are, how the two types are activated and which brain parts are involved in this.
Through the CNS psychological stressors exert wide-ranging effects on the physiology of the body
and some of these same effects on the body can be triggered by physiological stressors.
Stress: a long term disturbance of the psychological homeostasis.
Signs of stress
Arousal:
Confronted with a stressor an animal shows EEG arousal this is also termed activation. Although
there can be arousal without stress there cant be stress without arousal. In stress, animals take
both behavioural and physiological action. Because the sympathetic nervous system is usually excited
and thereby adrenalin and noradrenalin are released into the bloodstream. Hormones
(corticosteroids) are usually secreted at a high rate and they mobilize metabolic resources in the
body. The set of reactions is called the emergency reaction.
Types of stressor
External:
- For example: confrontation with predators, dealing with dominants of the group, competing
for food and reacting to rivals in overcrowded conditions.
- Coping strategies create opportunities to get away from the situation at hand or to make a
gesture to make the situation less dangerous.
- Persistence of arousal and failure to resolve the situation are associated with a range of
characteristic pathology, such as ulcers and blocking arteries.
Cognitive processes
- Corticosteroid secretion is sensitive to situations placed in context, for example novelty.
Novelty is not some intrinsic property of the environment rather the environment is novel in
context of previously experienced environments. Similarly loss of control in a situation
triggers the release or earning a reward smaller than your expectation is another trigger.
- Humans can stress themselves by thinking about endless problem solving.
- Informational discrepancy, reality differs from expectations or the inability to solve a
problem are internal stressors.
Physiological
- Blood loss or stretch of the bladder
- The mobilization of resources in this general emergency situation supports specific actions to
be become triggered. For example blood loss triggers specific behavioural homeostatic
actions such as seeking water and salt to correct the disturbance.
Behavioural indices
- When confronted with a stressor we might flee or fight and activate the sympathetic system.
- Or we might react with passivity and see what happens.
, - Failure of strategy over long periods of time constitutes stress
Four criteria of stress
1. Over time action occurs in responds to a situation but it fails to correct this situation.
2. 2. There is an excessive and protracted activity in neurohormonal systems.
3. There is vulnerability to certain pathology for example gastric ulceration, hypertension,
depression and disorders associated with suppression of the immune system.
4. There is a tendency to show apparently pointless behaviours such as stereotypies or inflicting
self-harm.
With humans low levels of stress might target voluntary behaviour for example work less and focus
more on other priorities.
Two neurohormonal systems
The autonomic nervous system (ANS)
Sympathetic branch:
- Emergencies activate the sympathetic branch of the ANS especially when action appears
possible.
- SNS activation triggers changes in the body such as an increased heart rate or dilated blood
vessels in the skeleton muscles.
- SNS activation also releases catecholamines: noradrenalin from the sympathetic neurons and
adrenalin and noradrenalin from the adrenal gland.
- Most noradrenalin originates from the terminals of neurons of the SNS, some originates from
the inner region of the adrenal gland (the adrenal medulla).
- Adrenalin and noradrenalin bind to two receptors: alpha and beta adrenergic receptors.
- When the beta receptors are occupied at a cardiac muscle the frequency of the heartbeat is
increased.
Parasympathetic branch
- Day to day maintenance for example promoting digestion.
- Increased activation occurs only in emergencies where no active strategy is perceived as
possible.
The hypothalamic pituitary adrenocortical system
- Corticosteroids are secreted from the outer layer of the adrenal gland, the adrenal cortex.
- The principle corticosteroid is cortisol.
- Stage 1: neurons with cell bodies at the paraventricular nucleus of the hypothalamus secrete
corticotropin releasing factor (CRF). At the pituitary gland occupation of the receptors by CRF
releases the adrenocorticotrophic hormone (ACTH).
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