Chapter 2:Chapter 2:The Physiology of StressThe Physiology of Stress

To understand the stress response, we To understand the stress response, we must possess a fundamental knowledge must possess a fundamental knowledge not only of psychology but of not only of psychology but of physiology as well.physiology as well.

- George - George EverlyEverly

The physiology of stressThe physiology of stress

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

PsychophysiologyPsychophysiology

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

The human brainThe human brainis divided into three levelsis divided into three levels::

the vegetative levelthe vegetative level

the limbic systemthe limbic system

the neocortical levelthe neocortical level

The Nervous SystemThe Nervous Systemcan be divided into:can be divided into:

the central nervous system (CNS)the central nervous system (CNS)– brain and brain and – spinal cordspinal cord

the peripheral nervous system (PNS)the peripheral nervous system (PNS)– consists of all neural pathways to the consists of all neural pathways to the

extremitiesextremities

The vegetative levelThe vegetative level

the lowest level of the brain is the lowest level of the brain is comprised of the:comprised of the:

– reticular formationreticular formation– brain stembrain stem

Reticular activating system Reticular activating system (RAS)(RAS)

The RAS is the link connecting the The RAS is the link connecting the brain to the spinal cord. brain to the spinal cord.

Several stress physiologists believe Several stress physiologists believe that this is the bridge joining that this is the bridge joining

the the mind and the body as one;mind and the body as one; this organ functions as a communi-this organ functions as a communi-

cation link between the mind cation link between the mind and and the body.the body.

The brain stemThe brain stem

The brain stem, comprised of the The brain stem, comprised of the pons, medulla oblongata, and pons, medulla oblongata, and mesencephalon, is responsible for mesencephalon, is responsible for

involuntary functions of the involuntary functions of the human body such as:human body such as:

heart beatheart beat– respirationrespiration– and vasomotor activityand vasomotor activity

The limbic systemThe limbic system

The limbic system is the emotional control The limbic system is the emotional control center and comprised of the:center and comprised of the:

– thalamusthalamus– hypothalamushypothalamus– pituitary glandpituitary gland

» also known as the master endocrine glandalso known as the master endocrine gland

These three glands work in unison to These three glands work in unison to maintain a level of homeostasismaintain a level of homeostasis

The neocortical levelThe neocortical level

The neocortex is the highest level of the The neocortex is the highest level of the brain.brain.

It is at this level that sensory information is It is at this level that sensory information is processed as a threat or a non-threat processed as a threat or a non-threat

and and where cognition takes place.where cognition takes place. This higher level of the brain can override This higher level of the brain can override

a a lower level and can influence lower level and can influence emotional emotional responses.responses.

Physiological systems involved Physiological systems involved in the stress response:in the stress response:

the nervous systemthe nervous system the endocrine systemthe endocrine system the immune systemthe immune system

The autonomic nervous systemThe autonomic nervous system(ANS)(ANS)

The ANS regulates visceral activities The ANS regulates visceral activities and vital organs, including: and vital organs, including:

– circulation, circulation, – digestion, digestion, – respiration, and respiration, and – temperature regulation temperature regulation

Two branches of the ANS that Two branches of the ANS that act to maintain homeostatic act to maintain homeostatic

balancebalance

the sympatheticthe sympathetic parasympathetic parasympathetic

The sympathetic and The sympathetic and parasympathetic systemsparasympathetic systems

Sympathetic nervous system:Sympathetic nervous system:

is responsible for the responses is responsible for the responses associated with the fight-or-associated with the fight-or-

flight flight responseresponse this physical arousal is stimulated this physical arousal is stimulated

through the release of through the release of catecholaminescatecholamines

– epinephrine (adrenaline)epinephrine (adrenaline)– norepinephrine (noradrenaline)norepinephrine (noradrenaline)

Parasympathetic nervous systemParasympathetic nervous system

maintains homeostasis through maintains homeostasis through the release of acetylcholine the release of acetylcholine (ACh)(ACh)

is responsible for energy is responsible for energy conservation and relaxationconservation and relaxation

The endocrine systemThe endocrine system

consists of a series of glands located consists of a series of glands located throughout the body which regulate throughout the body which regulate

metabolic functions that require metabolic functions that require endurance rather than endurance rather than

speedspeed the endocrine system is a network of four the endocrine system is a network of four

componentscomponents– glands, hormones, circulation, and target organsglands, hormones, circulation, and target organs

Endocrine systemEndocrine system

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

The nervous system and the The nervous system and the endocrine systemendocrine system

join together to form metabolic join together to form metabolic pathways or axes.pathways or axes.

there are three pathways:there are three pathways:– the ACTH axisthe ACTH axis– the vasopressin axis, andthe vasopressin axis, and– the thyroxine axisthe thyroxine axis

The ACTH pathwaysThe ACTH pathwaysstimulation of sensory nerves

stressor

hypothalamus

pituitary

ACTH

adrenal glands

stress hormonescortisol

aldosteroneepinephrine

Three stages of effects associated Three stages of effects associated with the stress responsewith the stress response

Immediate effects of stressImmediate effects of stress Intermediate effects of stressIntermediate effects of stress Prolonged effects of stressProlonged effects of stress

Immediate effects of stressImmediate effects of stress

sympathetic nervous responsesympathetic nervous response epinephrine and nor-epinephrine epinephrine and nor-epinephrine

releasedreleased time - 2 to 3 secondstime - 2 to 3 seconds like a phone calllike a phone call

Intermediate effects of stressIntermediate effects of stress

adrenal responseadrenal response epinephrine and nor-epinephrine epinephrine and nor-epinephrine

release from adrenal medullarelease from adrenal medulla time- 20 to 30 secondstime- 20 to 30 seconds like a telegramlike a telegram

Prolonged effects of stressProlonged effects of stress

ACTH, vasopressin and thyroxine ACTH, vasopressin and thyroxine affect various metabolic affect various metabolic

processesprocesses time - minutes, hours, days or time - minutes, hours, days or

weeksweeks like an “overnight delivery”like an “overnight delivery”

Immediateeffects

Intermediateeffects

Prolongedeffects

Phonecall

Western Uniontelegram

Overnightdelivery

Immediate, intermediate, and Immediate, intermediate, and prolonged effects of stressprolonged effects of stress