The Cybernetics of Stress: Causes, Chemicals, Consequences

The Cybernetics of Stress:Causes, Chemicals, Consequences 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, all students should develop an understanding of: • The cell • Biological evolution • Matter, energy, and organization of living systems • 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 functions. 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 anatomy…and 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://office.microsoft.com/clipart

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 d’etre for both interdisciplinary instruction and conceptual linkage within a particular subject area Source: http://office.microsoft.com/clipart

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 response. • 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 Source: www.ironordeal.com/clipart/persons/Confucius.htm.

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

Just What Exactly Is Stress? • Initially identified by Selye as “noxious agents.” • Became known as stress syndrome. Source: www.alnoorhospital.com/uploadedfiles/common/stress/jpg

Selye’s 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 body’s response to prolonged “wear and tear”).

Selye’s Final Analysis • Stress includes both internal and external factors. • 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” Source: www.saludparati.com/entres.htm

Selye’s Third Stage • Challenged by physiological, psychological, and environmental changes (stressors) • Failure to accommodate to changes can lead to exhaustion Source: www.bet.com/Health/Archives

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://facstaff.bloomu.edu/jhranitz/teaching/APHNT/Laboratory%20Pictures.htm

Neurons labeled with fluorescent proteins Source: Joshua Sanes, Harvard University. Lecture:”Neurons: how they look and what they do.7/11/2005

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://psych.hanover.edu/Krantz/neurotut.html

How an Action Potential Moves over the Neural Membrane • 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://www.miracosta.cc.ca.us/home/sfoster/neurons/action.htm

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 another. Source:http://www.miracosta.cc.ca.us/home/sfoster/neurons/animation.gif.

Perception of Pain • Perception of pain by nociceptors • Two types of nerve fibers involved: • “A” fibers (rapidly activated) • “C” fibers (activated more slowly) Source: www.acay.com.au/~mkause/fear%20helplessness/JPG

“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://office.microsoft.com/clipart

A Computer-Brain Analogy • Remember when the older computers didn’t have enough memory (RAM) to support more complex programs? • Continual bombardment of the brain by stress signals results in the inability to process and respond adequately to such signals. Source: http://office.microsoft.com/clipart

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).

Homeostasis • State of internal constancy or equilibrium necessary to maintain physiological health • Disrupted by stress Source: http://spwb.com/articles/anti-aging/stress.gif

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 system. • 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 Selye’s 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 Source: www.sciencebob.com/lab/bodyzone/brain/html

Physiological Feedback Loops Essential components of a feedback loop: • A sensory receptor sensitive to a disruptive stimulus • 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 (cont.) • 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 (cont.) • 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 Studies • 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 today’s pathologists to see not the future but the past. • Two stress-related animal studies illustrate this point.

Population Crowding Causes Stress in Deer • In the early 1920’s, 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. Source: www.whiskersinn.com/sale/images/3%20deer.jpg

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://homestudy.ibea.com/wildlifeID/043jackrabbit.htm

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://www.ratbehavior.org/Aggression.htm

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://office.microsoft.com/clipart

Behavior changes in females • Pregnancies were often aborted through miscarriage. • 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 fighting. • 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 AD. • Note that in the last three centuries or so, the growth curve becomes progressively exponential or logarithmic.

Source: http://wps.prenhall.com

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. Source: www.spokane7.com/…/archive/asp?mon=Jan2004

Population Density and Stress in Humans (cont.) • 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 levels. • This may be due to “self-treatment” by some individuals who feel “crowding stress” when moving to less densely populated areas (Regoeczi, 2002).

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 reasonable.

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)axis. • Trigger of the HPA axis results in the release of glucocorticoids (e.g., cortisol) from the adrenal gland.

The Cybernetics of Stress: Causes, Chemicals, Consequences