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The Cybernetics of Stress: Causes, Chemicals, Consequences


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Title: The Cybernetics of Stress: Causes, Chemicals, Consequences

The Cybernetics of StressCauses, Chemicals,
  • Richard W. Fardy, M.Ed.
  • Wilmington High School
  • Wilmington, MA

Relevant National Standards
  • Content Standard C
  • As a result of their activities in grades 9-12,
  • students should develop an understanding of
  • The cell
  • Biological evolution
  • Matter, energy, and organization of living
  • Behavior of organisms

Relevant Standards from the Massachusetts
Curriculum Frameworks (Health)
  • Standard 5
  • Students will acquire knowledge about emotions
    and physical health,and will learn skills to
    promote self-acceptance, make decisions and cope
    with stress.

Relevant Standards from the Massachusetts
Curriculum Frameworks (Biology 9-10)
  • Structure and Function of Cells
  • 2.1 Relate cell parts/organelles to their
  • Human Anatomy and Physiology
  • 4.2 Describe how the functions of individual
    systems within humans are integrated to maintain
    a homeostatic balance.
  • Evolution and Biodiversity
  • 5.1 Explain how comparative anatomyand other
    evidence support the theory of evolution.

Juggling and Authentic Learning
  • A juggler must simultaneously integrate sensory
    and muscular circuitry to keep all the objects in
    the air.

Source http//
Juggling and Authentic Learning (cont.)
  • In order for learning to be truly authentic,
    learning experiences need to show connections to
    real life.
  • Events do not always occur in a series of
    compartmentalized and disconnected boxes but
    still maintain connections to one another in some
    way and manner.

Link to Learn
  • The raison detre for both interdisciplinary
    instruction and conceptual linkage within a
    particular subject area

Source http//
Module Objectives
  • To be able to explain what happens in the three
    stages of the general adaptation syndrome (GAS).
  • To be able to identify the parts of a neuron and
    explain how neurons transmit messages.
  • To be able to define cybernetics and its
    connection to the nervous and endocrine systems.
  • To be able to define homeostasis, allostasis,and
    allostatic load, and explain the effects of
    stress on homeostatic equilibrium.

Module Objectives (continued)
  • To be able to describe the essential components
    of a biological feedback loop and to explain the
    differences in the effects of negative and
    positive loops.
  • To describe the psychological, neurological, and
    endocrine events that occur when anorexia nervosa
    results from stress.
  • To be able to describe how population density
    induces stress in animals and the possible
    implications for humans.

Module Objectives (continued)
  • To be able to explain the integration of the
    nervous and endocrine systems in the stress
  • To describe the general anatomy of the brain
    based on a sheep brain dissection.
  • To be able to explain how conditioning and
    learning may be accomplished in planaria and how
    stress may affect this process.

Ancient Proverb
  • I hear and I forget.
  • I see and I remember.
  • I do and I understand.
  • ?Confucius

Hans Selye (1907-1982)
  • Proposed general adaptation syndrome (GAS)
  • GAS theory first published in Nature in 1936
  • Described as bodys adaptive response to stress

Just What Exactly Is Stress?
  • Initially identified by Selye as noxious
  • Became known as stress syndrome.

Selyes Three Stages of Stress
  • Stage 1 The alarm reaction in which the body
    prepares itself for fight or flight.
  • Stage 2 Since the first stage cannot long be
    sustained, there is a general resistance to the
    stress which is established.
  • Stage 3 If the stress is continued for a long
    period of time, then eventual exhaustion results
    (the bodys response to prolonged wear and

Selyes Final Analysis
  • Stress includes both internal and external
  • Factors involve the nonspecific response of the
    body to any demand."

The Fight or Flight Response
  • Perceive extreme danger or distress
  • Neurons (nerve cells) in brain send entire body
    into high gear
  • Responsively prepare for fight or flight

Selyes Third Stage
  • Challenged by physiological, psychological, and
    environmental changes (stressors)
  • Failure to accommodate to changes can lead to

What Are Neurons?
  • Neurons are the specialized cells of which nerve
    tissue is composed.
  • Neurons have the ability to send messages to
    each other through the release of chemical
    substances called neurotransmitters.
  • Neurons are also electrical in nature,
    maintaining polarity through electrical gradients
    established by ions on the inside and outside of
    their cell membranes.
  • Neurons send electrical signals (action
    potentials) by depolarizing.

What Do Neurons Look Like?
  • Nerve smear containing neuron, axon, dendrite,
    cell body, nucleus, and nucleolus
  • Source http//

Neurons labeled with fluorescent proteins
Source Joshua Sanes, Harvard University.
LectureNeurons how they look and what they
What Are the Principal Parts of a Neuron?
  • A typical neuron consists of a soma or cell body
    where the nucleus is located, an axon which
    carries an impulse
  • (action potential) away from the soma, and
    dendrites which carry information to the soma.
  • Neurons interconnect by synapses (spaces over
    which neurotransmitters relay a message from one
    neuron to another).
  • Source http//

How an Action Potential Moves over the Neural
  • As the previously polarized nerve cell membrane
    becomes depolarized, the action potential coming
    from the dendrites to the cell body moves toward
    the synaptic junction.

Source http//
How Do Neurons Communicate?
  • Neurons do not physically touch each other.
  • Neurons communicate with one another through
    various neurotransmitters released from synaptic
    vesicles at the synaptic cleft
  • The synaptic cleft separates one neuron from
  • Sourcehttp//

Perception of Pain
  • Perception of pain by nociceptors
  • Two types of nerve fibers involved
  • A fibers (rapidly activated)
  • C fibers (activated more slowly)

Good and Bad Pain
  • A Fibers
  • Signal good pain
  • Serve as injury warning
  • Release glutamate
  • C Fibers
  • Signal more diffuse, chronic pain
  • Pain sources include tissue damage and cancer
  • Release substance P

Source http//
A Computer-Brain Analogy
  • Remember when the older computers didnt have
    enough memory (RAM) to support more complex
  • Continual bombardment of the brain by stress
    signals results in the inability to process and
    respond adequately to such signals.

Source http//
What Is Cybernetics?
  • Cybernetics sounds like either robot or computer
    jargon but actually refers to the study of
    communications and control systems in biological,
    mechanical and electronic systems.
  • Here, of course, we are only concerned with its
    biological applications (primarily in the nervous
    and endocrine systems).

  • State of internal constancy or equilibrium
    necessary to maintain physiological health
  • Disrupted by stress

Source http//
Disturbance of Homeostasis
  • Our bodies react to environmental changes
    (stressful or otherwise) by producing hormones
    and neurotransmitters.
  • These chemical substances are the messengers and
    mediators of the nervous system and endocrine
  • Stressful events cause the release of adrenalin
    and hormones (e.g., cortisol) from the adrenal
    medulla and cortex, respectively.

Then What Are Allostasis and Allostatic Load?
  • Since environmental conditions constantly
    fluctuate, allostasis refers to maintaining
    homeostasis despite these changes.
  • Likewise, allostatic load refers to Selyes
    notion of wear and tear that results from the
    inefficiency of those messenger and mediator
    processes over time.

Allostasis and Allostatic Load
  • Brain integrates and coordinates bodily responses
  • Physiological and behavioral stress responses
    result in allostatic adaptation
  • Over time allostatic load accumulates and can
    cause disease, even death

Physiological Feedback Loops
  • Essential components of a feedback loop
  • A sensory receptor sensitive to a disruptive
  • An afferent transmission pathway
  • A control center (i.e. the brain) serving and
    integrative input/output function
  • An efferent (motor) pathway
  • An effector to respond to the stimulus

Function of Feedback Loops
  • Negative feedback loops tend to maintain
    homeostasis (allostasis) by negating the effects
    of the disruptive stimulus.
  • Positive feedback loops enhance the disruptive
    stimulus and (in most instances) are harmful.
  • Unrelenting cycling of a POSITIVE feedback loop
    will result in death.

Psychological Preoccupation Becomes Physiological
in Anorexia
  • In a 1977 study published in the New England
    Journal of Medicine, researchers showed
    diminished degradation of plasma cortisol and low
    plasma triiodothyronine (active hormone
    controlling metabolic rate) in young women
    suffering from anorexia nervosa.

Psychological Preoccupation Becomes Physiological
  • The researchers concluded that anorexia involves
    the following cyclical sequence of events
  • A psychological event resulting in preoccupation
    with weight
  • Food avoidance leading to an adaptive starvation
    reaction with elevated cortisol levels
    mobilizing stored liver glycogen to increase
    blood glucose

Psychological Preoccupation Becomes Physiological
  • Elevated blood glucose level leading to further
    loss of appetite
  • Diminished levels of triiodothyronine levels from
    the thyroid gland inducing a protective or
    adaptive hypometabolic state (in response to the
    self-imposed starvation conditions) and
  • Resulting positive feedback loops (in the absence
    of timely medical intervention) promote adverse
    effects, even death.

Some Cautionary Tales from Animal
  • In ancient Etruscan and Roman civilizations a
    kind of fortune-telling ritual called haruspicy
    was practiced.
  • As a part of this ritual, the entrails
    (especially the liver) of animals were examined
    by the haruspex in order to predict the future.
  • Ironically, examination of the liver and other
    internal organs can enable todays pathologists
    to see not the future but the past.
  • Two stress-related animal studies illustrate this

Population Crowding Causes Stress in
  • In the early 1920s, a pair of deer was placed on
    a 150-acre island in Chesapeake Bay.
  • The deer population grew until the density
    reached about one deer per acre.
  • Then the deer began to die off (in the absence of
    known predators) despite the presence of adequate
    food and water.

The Post-mortem Findings
  • On autopsy the dead deer were found to have areas
    of atrophy in the liver tissue, marked decrease
    in liver glycogen, and hypoglycemia.
  • There was evidence of small (petechial) brain
    hemorrhages and both congestion and hemorrhage of
    the adrenal glands and kidneys.
  • These findings suggested what later was
    identified as adrenal stress syndrome.

Stress in Minnesota Jack Rabbits
  • In a 1939 study also reported in The Bulletin of
    the Atomic Scientists, Minnesota Jack Rabbits
    demonstrated rise and fall in population
    densities but when death rates and densities were
    high, they frequently entered into convulsive
    seizures or comatose states.
  • Liver and adrenal pathology, as
  • well as hypertension and
  • hypoglycemia associated with
  • adrenal stress syndrome,
  • were observed.

Source http//
Population Density and Behavior (Norway Rats)
  • In 1962, John Calhoun (of the National Institutes
    of Health) observed high mortality rates in
    confined wild Norway rats when population
    densities were high as a result of stress-induced
    behavioral changes.

Source http//
Population Density and Behavior (Norway Rats)
  • Calhoun conducted several experiments involving
    both a quarter-acre enclosure and 6 x 6
    interconnecting pens.
  • Calhoun made the following observations

Source http//
Behavior changes in females
  • Pregnancies were often aborted through
  • Considerable disruption of normal pre- and
    postpartum maternal behavior (i.e., failure to
    build proper nests, nurse offspring and transport
    litters) occurred.
  • Up to 25 of estrus females were so vigorously
    pursued by males that they did not survive.

Behavior changes in males
  • Some animals became hyperactive, constantly
  • These animals also became hypersexual and lost
    the ability to discriminate among estrus and
    non-estrus females, juveniles, and other males.
  • Some became cannibalistic.
  • Some became withdrawn, demonstrating no interest
    in social interaction.

Human Population Density
  • The following slide depicts human population
    growth in Europe from an estimated number of 20
    million people in 400 BC to 728 million in 2000
  • Note that in the last three centuries or so, the
    growth curve becomes progressively exponential or

Source http//
Population Density and Stress in Humans
  • Very few studies directly correlate stress of
    crowding with changes in the human brain.
  • Compelling evidence now available to link
    neurological changes in human brains to prolonged
    exposure to general stress.

Population Density and Stress in Humans
  • These neurological changes may very well be
    connected with behavioral changes as well.
  • For example, crime (which represents a form of
    social pathology) occurs at higher rates in urban
    than suburban areas, but the studies show mixed,
    non-linear correlations above certain density
  • This may be due to self-treatment by some
    individuals who feel crowding stress when
    moving to less densely populated areas (Regoeczi,

Population Density andStress in Humans (cont.)
  • However, the cages of Calhoun more closely
    resemble the stressful environments of crowded
    prisons and concentration camps.
  • Yet even under these conditions, there does not
    seem to be direct linear correlation between
    levels of crowding and levels of violence
    (Brooks, 2004).
  • Human physiological changes seem to be much more
    closely linked to animal models than behavioral
    ones, although some degree of extrapolation seems

Stress, Hormones, and the Brain
  • Once perceived, stress activates the hypothalamus
    of the brain, triggering a cascade of hormones
    through the hypothalamic-pituitary-adrenal (HPA)
  • Trigger of the HPA axis results in the release of
    glucocorticoids (e.g., cortisol) from the adrenal

Stress, Hormones and Brain The
Hypothalamic-Pituitary-Adrenal Axis
  • Some neurons in the hypothalamus produce
    corticotropin-releasing factor (CRF).
  • The synapses of these cells make contact with
    blood vessels, sending CRF to the adenohypophysis
    (anterior pituitary)
  • The pituitary then secretes adrenocorticotrophic
  • (ACTH) causing glucocorticoid release by the
    adrenal cortex.
  • At the same time the adrenal medulla produces
  • (The American Academy of Family Physicians)

What do glucocorticoids (such as cortisol)
  • Glucocorticoids increase blood glucose for the
    fight or flight reaction and thus have
    short-term benefits.
  • Over time, frequent release of these
    glucocorticoids adversely affects the hippocampus
    of the brain (the center of numerous
    glucocorticoid receptors).
  • Normal levels of these steroids maintain normal
    neuronal function in the hippocampus,
  • High levels of these steroids, however, adversely
    affect synaptic transmission and actually
    interfere with glucose uptake by neurons.
  • Resultant reduction of neural connections may
    responsively induce memory loss (Seckl, 2005).

Daily changes in cortisol in depressed
Source Neuroscience Presentation by Paul
Arfydio, Harvard University. July 14, 2005
Jonathan Seckls Conclusions
  • Both animals and humans may gradually develop a
    stress-related syndrome involving
  • Excess levels of glucocorticoids
  • Pathological changes in the structure and
    function of hippocampal cells
  • Neuronal death (sometimes)
  • Increased numbers of hippocampal glucocorticoid
    receptors, making the brain more sensitive to
    negative feedback control.
  • This may be one mechanism of action for certain
    antidepressant drugs.

Laboratory Activity Identifying the Brains
Basic Machinery
  • Perform a dissection of the sheep (Ovis) brain
    according to the excellent guide presented in the
    following link to the University of Scranton
    Neuroscience Program Dissection Guide
  • Sheep Brain Dissection Guide

Learning and Conditioning in Planaria (Dugesia
  • The planarian worm (Dugesia) is a small,
    free-living (i.e. non-parasitic) flatworm
    belonging to the phylum Platyhelminthes.
  • The planarian worm is acoelmate (without a body
    cavity enclosing the gut).
  • The planarian worm has a nervous system with 2
    light-sensitive eyespots, cephalic ganglia
    (brain), and 2 parallel longitudinal, ventral
    nerve cords.

Learning and Conditioning in Dugesia
  • Materials
  • Culture of live Dugesia
  • Plastic training maze
  • 6V lantern battery and bell wire
  • Camels hair artists brush

Learning and Conditioning in Dugesia
  • Protocol
  • Separate the Dugesia into two groups control and
  • Place the control animals at the beginning of the
    T-maze and allow them to move through it
    randomly. This will leave a layer of mucus on the
    maze and facilitate movement by others.
  • Note the numbers which move left, straight
    ahead, or right when they reach the maze
  • If they are reluctant to move at all, then gentle
    prodding with a soft brush may be helpful.

Learning and Conditioning in Dugesia
  • Now repeat the process with the experimental
  • This time apply an electric shock to the water,
    surrounding any worm which moves either straight
    ahead or to the right.
  • Repeat the experiment over a weeks time in order
    to observe and record the success of the learning

Learning and Conditioning in Dugesia
  • One variant of this experiment involves . . .
  • Keeping the animals in the dark and then exposing
    them to a bright light as an electrical shock is
    administered to the water
  • Then determining the number of trials required
    for the worms to recoil as though they were
    receiving an electrical shock when exposed only
    to the light source.

Observing the Effects of Stress on Learning in
  • Worms conditioned to light exposure experiment
    (and presumably stressed after repeated trials)
  • Comparatively tested against previously trained
    T-maze worms to determine possible relationship
    between stress of prior conditioning and
    performance in new trials

  • Boyer, R.M.,et al. Cortisol secretion and
    metabolism in anorexia nervosa.NEJM, 294
  • Brooks, Crystal. Overcrowding and violence in
    federal correctional institutionsAn empirical
    analysis. Retrieved from http//dspace.library.dre
  • Bresler, Jack B., ed. Human Ecology. Reading,MA.
  • Calhoun, John. Population density and social
    pathology. Scientific American. Feb.,1962.

References (continued)
  • Cox, Thomas. Black Hills State University.
    Learning and Conditioning Laboratory. PSYC305L.
    Fall, 2004. Retrieved from http//
  • Duane, Mary, et al. Inquiry in science using an
    animal behavior model. Retrieved from
  • Hoagland, Hudson. Cybernetics of population
    control. Bulletin of the Atomic Scientists.
  • Marieb, Elaine N. Essentials of Human Anatomy and
    Physiology. San Francisco. Addison-Wesley-Longman.

References (continued)
  • Massachusetts Department of Education.
    Massachusetts Curriculum Frameworks. Retrieved
    from http//
  • Mayer, Emeran A. The neurobiology of stress and
    emotions. Participate/Digestive Health
    Matters.Winter, 2001.
  • McEwen, Bruce and Teresa Seeman. Allostatic load
    and allostasis. Retrieved from
  • http//
  • August, 1999.
  • National Institute of Child Health and Human
    Development. NIH Backgrounder. http// Sept. 9, 2002.

References (continued)
  • National Research Council and National Academy of
    Sciences. National Sciences Education Standards.
    Retrieved from http//
  • Regoeczi, Wendy C. The impact of density The
    importance on nonlinearity and selection on
    flight and fight response. Social Forces. 81,
    2002. Retrieved from
  • http//
  • Seckl, Jonathan R. Glucocorticoids, aging, and
    nerve cell damage. Retrieved from
    11. June, 2005.
  • Society for Neuroscience. Brain Facts, a Primer
    on the Brain and Nervous System. Washington.
    Society for Neuroscience.

References (continued)
  • Spedding, M. and P. Lestage. Synaptic plasticity
    and neuropathology New approaches in drug
    discovery. MedSci (Paris). 211. Jan., 2005.
  • United States Dept. of Agriculture. Agricultural
    Research Service. Detecting stress in animals.
    Agricultural Research. Jan.,2002.
  • University of Scranton Neuroscience program.
    Welcome to the Sheep brain Dissection Guide.
    Retrieved from http//

Module Assessment Questions
  • 1. Describe how the general adaptation syndrome
    (GAS) may have evolved as an adaptation for
  • 2. What kinds of environmental changes induce
    stress in animals? In people?
  • 3. What are the main parts of a neuron, and how
    do neurons work?
  • 4. What are synapses, and how do they operate?
    How would neurons be different if they were
    directly connected (like soldered electrical

Module Assessment Questions
  • How is pain perceived, and what makes it a
    stressor? Distinguish between the perception of
    good and bad pain.
  • What evidence exists to show that high population
    density can induce stress?
  • What changes are induced in the brain and
    hormonal system as a result of stress?
  • What are the components of a feedback loop?
    Distinguish between the effects of negative and
    positive feedback loops.

Module Assessment Questions
  • Distinguish between allostasis and allostatic
  • What similarities and differences exist between
    humans and animals in how they respond to stress?
    How would you account for both the similarities
    and differences?
  • What is the hypothalamic-pituitary-adrenal (HPA)
    axis, and how does it operate?
  • What kinds of chemical substances are involved in
    the perception of stress and stress responses?
    How do they work?