Transcript
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The Cybernetics of Stress:
Causes, Chemicals, Consequences
Richard W. Fardy, M.Ed.Wilmington High School
Wilmington, MA
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Relevant National
StandardsContent Standard C:
As a result of their activities in grades 9-12, all
students should develop an understanding of:
1. The cell
2. Biological evolution
3. Matter, energy, and organization of livingsystems
4. Behavior of organisms
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Relevant Standards from the
Massachusetts Curriculum
Frameworks (Health) Standard 5:
“Students will acquire knowledgeabout emotions and physicalhealth,…and will learn skills topromote self-acceptance, make
decisions and cope with stress.”
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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.
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Juggling and Authentic Learning
A juggler mustsimultaneously
integratesensory andmuscular
circuitry to keepall the objects inthe air.
Source: http://office.microsoft.com/clipart
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Juggling and Authentic Learning(cont.)
In order for learning to be trulyauthentic, learning experiences need
to show connections to real life. Events do not always occur in a
series of compartmentalized and
disconnected boxes but still maintainconnections to one another in someway and manner.
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Link to Learn
The raison d’etre for
both interdisciplinaryinstruction andconceptual linkage
within a particularsubject area
Source: http://office.microsoft.com/clipart
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Module Objectives
To be able to explain what happens in thethree stages of the general adaptation
syndrome (GAS). To be able to identify the parts of a neuron
and explain how neurons transmitmessages.
To be able to define cybernetics and itsconnection to the nervous and endocrinesystems.
To be able to define homeostasis ,
allostasis ,and allostatic load , and explain
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Module Objectives
(continued) To be able to describe the essential
components of a biological feedback loop and to explain the differences in the effectsof negative and positive loops.
To describe the psychological, neurological,and endocrine events that occur whenanorexia nervosa results from stress.
To be able to describe how populationdensity induces stress in animals and thepossible implications for humans.
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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 braindissection.
To be able to explain how conditioningand learning may be accomplished inplanaria and how stress may affect
this process.
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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.
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Hans Selye (1907-1982)
Proposed general adaptationsyndrome (GAS)
GAS theory first published inNature in 1936
Described as body’s adaptiveresponse to stress
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Just What Exactly Is Stress?
Initiallyidentified by
Selye as“noxiousagents.”
Became knownas stress syndrome .
Source: www.alnoorhospital.com/uploadedfiles/common/stress/jpg
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Selye’s Three Stages of Stress
Stage 1: The alarm reaction in which thebody prepares itself for “fight or flight.”
Stage 2: Since the first stage cannot longbe sustained, there is a general resistanceto the stress which is established.
Stage 3: If the stress is continued for a
long period of time, then eventualexhaustion results (the body’s response toprolonged “wear and tear”).
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Selye’s Final Analysis
Stress includes both internaland external factors.
Factors involve the “nonspecificresponse of the body to any
demand."
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The “Fight or Flight” Response
1. Perceive extremedanger or distress
2. Neurons (nervecells) in brain sendentire body into“high gear”
3. Responsivelyprepare for “fightor flight”
Source: www.saludparati.com/entres.htm
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Selye’s Third Stage
Challenged byphysiological,
psychological, andenvironmentalchanges (stressors)
Failure to
accommodate tochanges can leadto exhaustion
Source: www.bet.com/Health/Archives
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What Are Neurons?
Neurons are the specialized cells of whichnerve tissue is composed.
Neurons have the ability to send “messages”to each other through the release of chemicalsubstances called neurotransmitters.
Neurons are also electrical in nature,
maintaining polarity through electricalgradients established by ions on the insideand outside of their cell membranes.
Neurons send electrical signals (action
potentials ) by depolarizing.
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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
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Neurons labeled with
fluorescent proteins
Source: Joshua Sanes, Harvard University. Lecture:”Neurons: how they look and what they do.7/11/2005
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What Are the Principal Parts
of a Neuron? A typical neuron consists of
a soma or cell body wherethe nucleus is located, anaxon which carries an
impulse(action potential ) awayfrom the soma, anddendrites which carryinformation to the soma.
Neurons interconnect bysynapses (spaces overwhich neurotransmittersrelay a message from oneneuron to another).
Source: http://psych.hanover.edu/Krantz/neurotut.html
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How an Action PotentialMoves over the Neural
Membrane As the previously
polarized nerve
cell membranebecomesdepolarized, theaction potential
coming from thedendrites to thecell body movestoward the
synaptic junction.Source:
http://www.miracosta.cc.ca.us/home/sfoster/neurons/action.htm
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How Do Neurons Communicate?
Neurons do notphysically toucheach other.
Neuronscommunicate withone another throughvariousneurotransmittersreleased fromsynaptic vesicles atthe synaptic cleft
The synaptic cleftseparates oneneuron from
another.
Source:http://www.miracosta.cc.ca.us/home/sfoster/neurons/animation.gif.
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Perception of Pain
Perception of painby nociceptors
Two types of nervefibers involved:
1. “A” fibers (rapidlyactivated)
2. “C” fibers (activatedmore slowly)
Source: www.acay.com.au/~mkause/fear%20helplessness/JPG
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“Good” and “Bad” Pain
“A” Fibers:
Signal “good pain”
Serve as injury warning Release glutamate
“C” Fibers:
Signal more diffuse, chronicpain
Pain sources include tissue
damage and cancer“ ”
Source: http://office.microsoft.com/clipart
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A Computer-Brain Analogy
Remember when the oldercomputers didn’t haveenough memory (RAM) tosupport more complexprograms?
Continual bombardment
of the brain by stresssignals results in theinability to process andrespond adequately tosuch signals.
Source: http://office.microsoft.com/clipart
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What Is Cybernetics?
Cybernetics sounds like either robot orcomputer jargon but actually refers to
the study of communications and control systems in biological, mechanical and electronic systems .
Here, of course, we are only concernedwith its biological applications(primarily in the nervous and endocrinesystems).
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Homeostasis
State of internalconstancy orequilibriumnecessary tomaintainphysiological
health
Disrupted bystress
Source: http://spwb.com/articles/anti-aging/stress.gif
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Disturbance of Homeostasis
Our bodies react to environmental changes(stressful or otherwise) by producinghormones and neurotransmitters.
These chemical substances are themessengers and mediators of the nervoussystem and endocrine system.
Stressful events cause the release of adrenalin and hormones (e.g., cortisol) fromthe adrenal medulla and cortex,respectively.
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Then What Are Allostasis
and Allostatic Load? Since environmental conditions constantly
fluctuate, allostasis refers to maintaining
homeostasis despite these changes. Likewise, allos tatic lo ad refers to Selye’s
notion of “wear and tear” that results fromthe inefficiency of those messenger and
mediator processes over time.
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Allostasis and Allostatic Load
Brain integratesand coordinatesbodily responses
Physiological andbehavioral stressresponses result inallostatic adaptation
Over time allostaticload accumulatesand can causedisease, even deathSource: www.sciencebob.com/lab/bodyzone/brain/html
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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
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Function of Feedback Loops
Negative feedback loops tend tomaintain homeostasis (allostasis ) by
negating the effects of the disruptivestimulus.
Positive feedback loops enhance the
disruptive stimulus and (in mostinstances) are harmful.
Unrelenting cycling of a POSITIVE
feedback loop will result in death.
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Psychological PreoccupationBecomes Physiological in Anorexia
In a 1977 study published in the New England Journal of Medicine,
researchers showed diminisheddegradation of plasma cortisol and lowplasma triiodothyronine (active
hormone controlling metabolic rate) inyoung women suffering from anorexianervosa.
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Psychological PreoccupationBecomes Physiological (cont.)
The researchers concluded that anorexiainvolves the following cyclical sequence
of events:1. A psychological event resulting in
preoccupation with weight;
2. Food avoidance leading to an adaptive
“starvation reaction” with elevatedcortisol levels mobilizing stored liverglycogen to increase blood glucose;
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Psychological PreoccupationBecomes Physiological (cont.)
3. Elevated blood glucose level leading tofurther loss of appetite;
4. Diminished levels of triiodothyroninelevels from the thyroid gland inducing aprotective or adaptive hypometabolicstate (in response to the self-imposed
starvation conditions); and5. Resulting positive feedback loops (in the
absence of timely medical intervention)promote adverse effects, even death.
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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 (especiallythe liver) of animals were examined by theharuspex in order to predict the future.
Ironically, examination of the liver and other
internal organs can enable today’s pathologiststo see not the future but the past.
Two stress-related animal studies illustrate thispoint.
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Population Crowding CausesStress in Deer
In the early 1920’s, apair of deer was placedon a 150-acre island inChesapeake Bay.
The deer populationgrew until the densityreached about one deerper acre.
Then the deer began todie off (in the absence of known predators)despite the presence of adequate food and
water. Source:www.whiskersinn.com/sale/images/3%20deer.jpg
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The Post-mortem Findings
On autopsy the dead deer were found tohave areas of atrophy in the liver tissue,
marked decrease in liver glycogen, andhypoglycemia.
There was evidence of small (petechial)brain hemorrhages and both congestion
and hemorrhage of the adrenal glands andkidneys.
These findings suggested what later wasidentified as adrenal stress syndrome .
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Stress in Minnesota Jack Rabbits
In a 1939 study also reported inThe Bulletin of the Atomic Scientists, Minnesota JackRabbits demonstrated rise andfall in population densities but when death rates and densitieswere high, they frequentlyentered into convulsive seizuresor comatose states.
Liver and adrenal pathology, aswell as hypertension andhypoglycemia associated withadrenal stress syndrome ,were observed.
Source:http://homestudy.ibea.com/wildlifeID/043jackrabbit.htm
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Population Density andBehavior (Norway Rats) In 1962, John Calhoun
(of the NationalInstitutes of Health)
observed highmortality rates inconfined wild Norwayrats when populationdensities were high asa result of stress-induced behavioral
changes.Source: http://www.ratbehavior.org/Aggression.htm
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Population Density andBehavior (Norway Rats)
Calhoun conductedseveral experiments
involving both aquarter-acreenclosure and 6’ x 6’interconnecting
pens. Calhoun made the
followingobservations:
Source: http://office.microsoft.com/clipart
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Behavior changes in females
1. Pregnancies were often abortedthrough miscarriage.
2. Considerable disruption of normalpre- and postpartum maternalbehavior (i.e., failure to buildproper nests, nurse offspring and
transport litters) occurred.3. Up to 25% of estrus females were
so vigorously pursued by males
that they did not survive.
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Behavior changes in males
1. Some animals became hyperactive,constantly fighting.
2. These animals also became hypersexualand lost the ability to discriminateamong estrus and non-estrus females,
juveniles, and other males.
3. Some became cannibalistic.4. Some became withdrawn, demonstrating
no interest in social interaction.
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Human Population Density
The following slide depicts humanpopulation growth in Europe from an
estimated number of 20 millionpeople in 400 BC to 728 million in2000 AD.
Note that in the last three centuriesor so, the growth curve becomesprogressively exponential orlogarithmic.
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Source: http://wps.prenhall.com
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Population Density and Stressin Humans
Very few studiesdirectly correlate stressof crowding with
changes in the humanbrain.
Compelling evidencenow available to link
neurological changes inhuman brains toprolonged exposure to
general stress.Source: www.spokane7.com/…/archive/asp?mon=Jan2004
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Population Density andStress in Humans (cont.)
These neurological changes may very well beconnected with behavioral changes as well.
For example, crime (which represents a form of
social pathology) occurs at higher rates in urbanthan suburban areas, but the studies showmixed, non-linear correlations above certaindensity levels.
This may be due to “self -treatment” by some
individuals who feel “crowding stress” whenmoving to less densely populated areas (Regoeczi,2002).
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Population Density andStress in Humans (cont.) However, the cages of Calhoun more closely
resemble the stressful environments of crowdedprisons and concentration camps.
Yet even under these conditions, there does notseem to be direct linear correlation betweenlevels of crowding and levels of violence (Brooks,2004).
Human physiological changes seem to be much
more closely linked to animal models thanbehavioral ones, although some degree of extrapolation seems reasonable.
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Stress, Hormones, and the Brain
Once perceived, stress activates thehypothalamus of the brain,
triggering a cascade of hormonesthrough the hypothalamic-pituitary- adrenal (HPA) axis.
Trigger of the HPA axis results inthe release of glucocorticoids (e.g.,cortisol) from the adrenal gland.
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Stress, Hormones and Brain: TheHypothalamic-Pituitary-Adrenal
Axis Some neurons in the hypothalamus producecorticotropin-releasingfactor (CRF).
The synapses of these cells
make contact with bloodvessels, sending CRF to theadenohypophysis (anteriorpituitary)
The pituitary then secretesadrenocorticotrophic
hormone(ACTH) causingglucocorticoid release bythe adrenal cortex.
At the same time theadrenal medulla produces
adrenalin.
Source:www.aafp.org/afp/20000901/1119_f2.gif.(The American Academy of Family Physicians)
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What do glucocorticoids(such as cortisol) do?
Glucocorticoids increase blood glucose for the“fight or flight” reaction and thus have short-termbenefits.
Over time, frequent release of theseglucocorticoids adversely affects the hippocampusof the brain (the center of numerous glucocorticoidreceptors).
Normal levels of these steroids maintain normalneuronal function in the hippocampus,
High levels of these steroids, however, adverselyaffect synaptic transmission and actuallyinterfere with glucose uptake by neurons.
Resultant reduction of neural connections mayresponsively induce memory loss (Seckl, 2005).
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Daily changes in cortisolin depressed patients
Source: Neuroscience Presentation by Paul Arfydio, Harvard University. July 14, 2005
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Jonathan Seckl’s Conclusions
Both animals and humans may graduallydevelop a stress-related syndrome involving:
1. Excess levels of glucocorticoids
2. Pathological changes in the structure andfunction of hippocampal cells
3. Neuronal death (sometimes)4. Increased numbers of hippocampal
glucocorticoid receptors, making the brainmore sensitive to negative feedback control. This may be one mechanism of action for
certain antidepressant drugs.
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Laboratory Activity: Identifyingthe Brain’s Basic Machinery
Perform a dissection of the sheep(Ovis) brain according to the
excellent guide presented in thefollowing link to the University of Scranton Neuroscience Program
Dissection Guide : Sheep Brain Dissection Guide
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Learning and Conditioningin Planaria (Dugesia sp.)
The planarian worm(Dugesia) is a small, free-living (i.e. non-parasitic)
flatworm belonging to the phylum Platyhelminthes.
The planarian worm isacoelmate (without a bodycavity enclosing the gut).
The planarian worm has anervous system with 2light-sensitive eyespots,cephalic ganglia (“brain”),and 2 parallel longitudinal,
ventral nerve cords.Source:
www.anselm.edu/…/genbios/surveybi04.html
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Learning and Conditioningin Dugesia (cont.)
Materials:
Culture of live Dugesia
Plastic training maze 6V lantern battery and bell wire
Camel’s hair artist’s brush
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Learning and Conditioningin Dugesia (cont.)
Protocol:
Separate the Dugesia into two groups: control and experimental .
Place the control animals at the beginning of theT-maze and allow them to move through itrandomly. This will leave a layer of mucus on themaze and facilitate movement by others.
Note the numbers which move left, straightahead, or right when they reach the mazeintersection.
If they are reluctant to move at all, then gentleprodding with a soft brush may be helpful.
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Learning and Conditioningin Dugesia (cont.)
Now repeat the process with theexperimental group:
This time apply an electric shock to thewater, surrounding any worm whichmoves either straight ahead or to theright.
Repeat the experiment over a week’stime in order to observe and record thesuccess of the learning process.
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Learning and Conditioningin Dugesia (cont.)
One variant of this experiment involves . . .
Keeping the animals in the dark and then
exposing them to a bright light as anelectrical shock is administered to thewater;
Then determining the number of trials
required for the worms to recoil as thoughthey were receiving an electrical shockwhen exposed only to the light source.
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Observing the Effects of Stresson Learning in Dugesia
Worms conditioned to light exposureexperiment (and presumably
stressed after repeated trials) Comparatively tested against
previously trained T-maze worms todetermine possible relationship
between stress of prior conditioningand performance in new trials
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References
Boyer, R.M.,et al. Cortisol secretion and metabolism inanorexia nervosa.NEJM, 294 ( 4),1977.
Brooks, Crystal. Overcrowding and violence in federal
correctional institutions:An empirical analysis. Retrievedfrom http://dspace.library.drexel.edu.
Bresler, Jack B., ed. Human Ecology. Reading,MA. Addison-Wesley.1966.
Calhoun, John. Population density and social pathology.Scientific American . Feb.,1962.
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References (continued)
Cox, Thomas. Black Hills State University. Learning andConditioning Laboratory. PSYC305L. Fall, 2004. Retrievedfrom http://www.bhsu.edu.
Duane, Mary, et al. Inquiry in science using an animalbehavior model. Retrieved fromhttp://www.woodrowwilson.org/teachers/bi/1998/planaria/index.htm.
Hoagland, Hudson. Cybernetics of population control. Bulletin
of the Atomic Scientists . Feb.,1964.
Marieb, Elaine N. Essentials of Human Anatomy and Physiology. San Francisco. Addison-Wesley-Longman. 2000.
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References (continued)
Massachusetts Department of Education. Massachusetts Curriculum Frameworks. Retrieved from http://www.doe.mass.edu/frameworks.
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 fromhttp://www.macses.uscf.edu/Research/allostatic/notebook/allostatic. August, 1999.
National Institute of Child Health and Human Development. NIHBackgrounder. http://www.nichd.nih.gov. Sept. 9, 2002.
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References (continued)
National Research Council and National Academy of Sciences.National Sciences Education Standards. Retrieved fromhttp://www.nap.edu/readingroom/books/nses/html/index.html.
Regoeczi, Wendy C. The impact of density: The importance on
nonlinearity and selection on flight and fight response. Social Forces . 81, 2002. Retrieved fromhttp://www.ncsociology.org/sociationtoday/v22/crowding.htm.
Seckl, Jonathan R. Glucocorticoids, aging, and nerve cell damage.Retrieved fromhttp://neuroendo.org.uk/index/php/content/view/18/11. June, 2005.
Society for Neuroscience. Brain Facts, a Primer on the Brain and Nervous System. Washington. Society for Neuroscience.
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References (continued)
Spedding, M. and P. Lestage. Synaptic plasticityand neuropathology: New approaches in drugdiscovery. MedSci (Paris). 21:1. Jan., 2005.
United States Dept. of Agriculture. AgriculturalResearch Service. Detecting stress in animals.
Agricultural Research . Jan.,2002.
University of Scranton Neuroscience program.“Welcome to the Sheep brain Dissection Guide.”Retrieved from http://www.humboldt.edu.
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Module AssessmentQuestions
1. Describe how the general adaptation syndrome (GAS) may have evolved as anadaptation for survival.
2. What kinds of environmental changesinduce stress in animals? In people?
3. What are the main parts of a neuron, andhow do neurons work?
4. What are synapses, and how do theyoperate? How would neurons be different if they were directly connected (like solderedelectrical wires)?
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Module Assessment Questions(II)
5. How is pain perceived, and what makes ita stressor? Distinguish between theperception of “good” and “bad” pain.
6. What evidence exists to show that highpopulation density can induce stress?
7. What changes are induced in the brainand hormonal system as a result of stress?
8. What are the components of a feedbackloop? Distinguish between the effects of negative and positive feedback loops.
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Module Assessment Questions(III)
9. Distinguish between allostasis andallostatic load .
10. What similarities and differences exist
between humans and animals in how theyrespond to stress? How would you accountfor both the similarities and differences?
11. What is the hypothalamic-pituitary-
adrenal (HPA) axis , and how does itoperate?
12. What kinds of chemical substances areinvolved in the perception of stress and
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