Chapter 2: The Physiology of Stress To understand the stress response, we must possess a fundamental knowledge not only of psychology but of physiology as well. - George Everly

The physiology of stress Hans Selye, considered by many as the father of the study of stress, developed the idea that there was a direct relationship between chronic stress and excessive wear and tear throughout the body.

Psychophysiology is a term to describe the body’s physiological reaction to perceived stressors suggesting that the stress response is a mind-body phenomenon.

The human brain is divided into three levels : the vegetative level the vegetative level the limbic system the limbic system the neocortical level the neocortical level

The Nervous System can be divided into: n the central nervous system (CNS) – brain and – spinal cord n the peripheral nervous system (PNS) – consists of all neural pathways to the extremities

The vegetative level n the lowest level of the brain is comprised of the: – reticular formation – brain stem

Reticular activating system (RAS) n The RAS is the link connecting the brain to the spinal cord. n Several stress physiologists believe that this is the bridge joining the mind and the body as one; n this organ functions as a communi- cation link between the mind and the body.

The brain stem n The brain stem, comprised of the pons, medulla oblongata, and mesencephalon, is responsible for involuntary functions of the human body such as: n heart beat – respiration – and vasomotor activity

The limbic system n The limbic system is the emotional control center and comprised of the: – thalamus – hypothalamus – pituitary gland » also known as the master endocrine gland n These three glands work in unison to maintain a level of homeostasis

The neocortical level n The neocortex is the highest level of the brain. n It is at this level that sensory information is processed as a threat or a non-threat and where cognition takes place. n This higher level of the brain can override a lower level and can influence emotional responses.

Physiological systems involved in the stress response: À the nervous system Á the endocrine system  the immune system

The autonomic nervous system (ANS) n The ANS regulates visceral activities and vital organs, including: – circulation, – digestion, – respiration, and – temperature regulation

Two branches of the ANS that act to maintain homeostatic balance n the sympathetic n parasympathetic

The sympathetic and parasympathetic systems

Sympathetic nervous system: n is responsible for the responses associated with the fight-or-flight response n this physical arousal is stimulated through the release of catecholamines – epinephrine (adrenaline) – norepinephrine (noradrenaline)

Parasympathetic nervous system n maintains homeostasis through the release of acetylcholine (ACh) n is responsible for energy conservation and relaxation

The endocrine system n consists of a series of glands located throughout the body which regulate metabolic functions that require endurance rather than speed n the endocrine system is a network of four components – glands, hormones, circulation, and target organs

Endocrine system n the glands most closely involved with the stress response are the: – pituitary, – thyroid, and – adrenal glands

The nervous system and the endocrine system n join together to form metabolic pathways or axes. n there are three pathways: – the ACTH axis – the vasopressin axis, and – the thyroxine axis

The ACTH pathways stimulation of sensory nerves stressor hypothalamus pituitary ACTH adrenal glands stress hormones cortisol aldosterone epinephrine

Three stages of effects associated with the stress response n Immediate effects of stress n Intermediate effects of stress n Prolonged effects of stress

Immediate effects of stress n sympathetic nervous response n epinephrine and nor-epinephrine released n time - 2 to 3 seconds n like a phone call

Intermediate effects of stress n adrenal response n epinephrine and nor-epinephrine release from adrenal medulla n time- 20 to 30 seconds n like a telegram

Prolonged effects of stress n ACTH, vasopressin and thyroxine affect various metabolic processes n time - minutes, hours, days or weeks n like an “overnight delivery”

Immediate effects Intermediate effects Prolonged effects Phone call Western Union telegram Overnight delivery Immediate, intermediate, and prolonged effects of stress