Psychophysiology of stress response
by Stephen Palmer
This article provides an insight into what happens at a physiological level when a person becomes stressed. Although this article may seem rather complicated, it is an oversimplification of what happens. It is suggested that readers interested in increasing their understanding about this topic refer to advanced texts that are available.
The Stress Response
Often a crucial part of the stress response is the initial appraisal by the person. Hence it can be the psychological component that triggers the stress response. If a person perceives that they are in threatening situations that they are unable to cope with, then messages are carried along neurones from the cerebral cortex (where the thought processes occur) and the limbic system to the Hypothalamus. This has a number of discrete parts.
The Anterior Hypothalamus produces sympathetic arousal of the Autonomic Nervous System (ANS). The ANS is an automatic system that controls the heart, lungs, stomach, blood vessels and glands. Due to its action we do not need to make any conscious effort to regulate our breathing or heart beat. The ANS consists of two different systems: the sympathetic nervous system and the parasympathetic nervous system. Essentially, the parasympathetic nervous system conserves energy levels. It increases bodily secretions such as tears, gastric acids, mucus and saliva which help to defend the body and help digestion. Chemically, the parasympathetic system sends its messages by a neurotransmitter called acetylcholine which is stored at nerve endings.
Unlike the parasympathetic nervous system which aids relaxation, the sympathetic nervous system prepares the body for action. In a stressful situation, it quickly does the following:
Increases strength of skeletal muscles
Decreases blood clotting time
Increases heart rate
Increases sugar and fat levels
Reduces intestinal movement
Inhibits tears, digestive secretions.
Relaxes the bladder
Increases mental activity
Inhibits erection/vaginal lubrication
Constricts most blood vessels but dilates those in heart/leg/arm muscles
The main sympathetic neurotransmitter is called noradrenaline which is released at the nerve endings. The stress response also includes the activity of the adrenal, pituitary and thyroid glands.
The two adrenal glands are located one on top of each kidney. The middle part of the adrenal gland is called the adrenal medulla and is connected to the sympathetic nervous system by nerves. Once the latter system is in action it instructs the adrenal medulla to produce adrenaline and noradrenaline (catecholamines) which are released into the blood supply. The adrenaline prepares the body for flight and the noradrenaline prepares the body for fight. They increase both the heart rate, and the pressure at which the blood leaves the heart; they dilate bronchial passages and dilate coronary arteries; skin blood vessels constrict and there is an increase in metabolic rate. Also gastrointestinal system activity reduces which leads to a sensation of butterflies in the stomach.
Lying close to the hypothalamus in the brain is an endocrine gland called the pituitary. In a stressful situation, the anterior hypothalamus activates the pituitary. The pituitary releases adrenocorticotrophic hormone (ACTH) into the blood which then activates the outer part of the adrenal gland, the adrenal cortex. This then synthesises cortisol which increases arterial blood pressure, mobilises fats and glucose from the adipose (fat) tissues, reduces allergic reactions, reduces inflammation and can decrease lymphocytes that are involved in dealing with invading particles or bacteria. Consequently, increased cortisol levels over a prolonged period of time lowers the efficiency of the immune system. The adrenal cortex releases aldosterone which increases blood volume and subsequently blood pressure. Unfortunately, prolonged arousal over a period of time due to stress can lead to essential hypertension.
The pituitary also releases thyroid stimulating hormone which stimulates the thyroid gland, which is located in the neck, to secrete thyroxin. Thyroxin increases the metabolic rate, raises blood sugar levels, increases respiration/heart rate/blood pressure/and intestinal motility. Increased intestinal motility can lead to diarrhoea. (It is worth noting that an over-active thyroid gland under normal circumstances can be a major contributory factor in anxiety attacks. This would normally require medication.)
The pituitary also releases oxytocin and vasopressin which contract smooth muscles such as the blood vessels. Oxytocin causes contraction of the uterus. Vasopressin increases the permeability of the vessels to water therefore increasing blood pressure. It can lead to contraction of the intestinal musculature.
If the person perceives that the threatening situation has passed then the parasympathetic nervous system helps to restore the person to a state of equilibrium. However, for many people they perceive everyday of their life as stressful. Unfortunately, the prolonged effect of the stress response is that the body's immune system is lowered and blood pressure is raised which may lead to essential hypertension and headaches. The adrenal gland may malfunction which can result in tiredness with the muscles feeling weak; digestive difficulties with a craving for sweet, starchy food; dizziness; and disturbances of sleep.
Below are some of the possible symptoms of stress. Please note that these symptoms can also occur with a range of medical or psychological disorders. When in doubt, do consult your doctor, psychologist or consultant.
POSSIBLE RESPONSES TO STRESS (see Palmer and Dryden, 1995)
Increased nicotine/caffeine intake
Loss of appetite/overeating
Impaired speech/voice tremor
Poor time management
Withdrawing form relationships
Type A behaviour e.g. talking/walking/eating
Decreased/increased sexual activity
Poor eye contact
Rapid heart beat
Premature ejaculation/erectile dysfunction
Limited sensual and sexual awareness
Butterflies in stomach
Spasms in stomach
Self and/or others dying/suicide
Nightmares/distressing recurring dreams
I must perform well
Life should not be unfair
Low frustration statements e.g. I can't stand it.
I must be in control
It's awful, terrible, horrible, unbearable etc.
I must have what I want
I must obey 'my' moral code and rules
Others must approve of me
Cognitive distortions e.g. all or nothing thinking
Passive/aggressive in relationships
Put other' needs before own
Makes friends easily/with difficulty
Use of: drugs, stimulants, alcohol, tranquillizer, hallucinogens
High blood pressure/coronary heart disease(angina/heart attack)
Lowered immune system
Poor nutrition, exercise and recreatio
Biologically based mental disorders
Palmer, S. and Dryden, W. (1995). Counselling for Stress Problems. London: Sage.
Centre website: www.managingstress.com