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One of the best-understood neurotransmitters, acetylcholine (ACh), plays a role in
PRACTICE
Research Methods & Design
(SP 2)
(20 minutes) This would be a good
time to review the experimental
method within the context of
neurotransmission with your
students. Place them in small
groups. Then ask each group to
design a study that would allow
them to conclude that vigorous
exercise causes the release of
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
endorphins. Remind them that they
need to randomly assign some
participants to exercise and others
not to exercise (the independent
variable), then measure all
participants’ endorphin levels (the
dependent variable), and finally
compare the two groups for the
study to be experimental. Have
each group share their study
design with the class. Follow the
presentations with a discussion of
why we can only draw cause-effect
conclusions from studies that use
experimental methods. Copyright © Bedford, Freeman & Worth Publishers.
TEACH 1.3-3
Enrichment
Tell students that strenuous exercise
triggers the release of endorphins.
Studies of seasoned runners, for
example, show that during a long,
difficult workout the nervous system
can dip into its endorphin reserves
and not only block pain messages but
also produce the “runner’s high.” The
03_myersAPpsychology4e_28116_ch01_002_163.indd
endorphin system can also be brought
into action by neurostimulation ther-
apy. In this pain- reducing technique,
electrodes are pasted to the skin near
an injury, and a slight electrical current
is delivered. Low-frequency, high-
intensity impulses stimulate endorphin
release. Olympic and professional
athletes have used this technology.
34 Unit 1 Biological Bases of Behavior
03_HammerTE4e_47547_ch01_2a_163_4pp.indd 34
learning and memory. ACh also enables muscle action, by acting as the messenger at
every junction between motor neurons (which carry information from the brain and spi-
nal cord to the body’s tissues) and skeletal muscles. When ACh is released to our muscle
cell receptors, the targeted muscle contracts. If ACh transmission is blocked, as happens
during some kinds of anesthesia, with some poisons, and with the neuromuscular disease
myasthenia gravis, the muscles cannot contract. The result is weakness, difficulties with
muscle control, or paralysis.
Candace Pert and Solomon Snyder (1973) made an exciting discovery about neuro-
transmitters when they attached a harmless radioactive tracer to morphine, an opioid drug
that elevates mood and eases pain. As the researchers tracked the morphine in an animal’s
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AP Science Practice brain, they noticed it was binding to receptors in areas linked with mood and pain sensa-
tions. But why would the brain have these “opioid receptors”? Why would it have a chemi-
Research cal lock, unless it also had a key — a natural painkiller — to open it?
To conclude that vigorous exercise Researchers soon confirmed that the brain does, indeed, produce its own naturally
causes the release of endorphins,
researchers would need to manip- occurring opioids. Our body releases several types of neurotransmitter molecules similar to
morphine in response to pain and vigorous exercise. These endorphins (short for endog-
ulate (or randomly assign) some
participants to exercise and others enous [produced within] morphine) help explain good feelings such as the “runner’s high,”
not to exercise, then measure all the painkilling effects of acupuncture, and the indifference to pain in some severely injured
participants’ endorphin levels and
compare the two groups. You can people (Boecker et al., 2008; Fuss et al., 2015). Physician Lewis Thomas (1983) called the
draw cause-effect conclusions
endorphins “a biologically universal act of mercy. I cannot explain it, except to say that
from studies that use an experi- I would have put it in had I been around at the very beginning, sitting as a member of a
mental research design.
planning committee.”
How Drugs and Other Chemicals Alter Neurotransmission
AP Exam Tip If natural endorphins lessen pain and boost mood, why shouldn’t we increase this effect by
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flooding the brain with artificial opioids, thereby intensifying the brain’s own “feel-good”
Be clear on this: Neurotransmitters chemistry? The answer: Because that would disrupt the brain’s chemical balancing act.
are produced inside the body;
When flooded with opioid drugs such as heroin, morphine, and fentanyl, the brain — to
they can excite and inhibit neural maintain its chemical balance — may stop producing its own natural opioids. When the
communication. Drugs and other
chemicals come from outside the drug is withdrawn, the brain may then be deprived of any form of opioid, causing intense
body; they can have an agonistic
effect or an antagonistic effect on discomfort. For suppressing the body’s own neurotransmitter production, nature charges
a price.
neurotransmission. Students have Drugs and other chemicals affect brain chemistry, often by either exciting or inhib-
confused these concepts on the
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AP exam. iting neurons’ firing. Agonist molecules increase a neurotransmitter’s action. Some
agonists increase the production or release of neurotransmitters, or block synaptic
reuptake. Other agonists may be similar enough to a neurotransmitter to bind to its
receptor and mimic its excitatory or inhibitory effects. Some opioid drugs are agonists
endorphins [en-DOR-fins] and produce a temporary “high” by amplifying normal sensations of arousal or plea-
sure (Figure 1.3-6).
“morphine within”; natural,
opioid-like neurotransmitters
Antagonists decrease a neurotransmitter’s action by blocking production or release.
linked to pain control and to Botulin, a poison that can grow in improperly canned food, causes paralysis by blocking
pleasure. ACh release. (Small injections of botulin — known by the brand name Botox ™ — smooth
agonist a molecule that wrinkles by paralyzing the underlying facial muscles.) These antagonists are enough like the
increases a neurotransmitter’s
action. natural neurotransmitter to occupy its receptor site and block its effect, but are not similar
antagonist a molecule enough to stimulate the receptor (rather like foreign coins that fit into, but won’t operate,
that inhibits or blocks a a vending machine). Curare, a poison that some South American Indigenous people have
neurotransmitter’s action. applied to hunting-dart tips, occupies and blocks ACh receptor sites on muscles, producing
paralysis in their prey.
34 Unit 1 Biological Bases of Behavior
TEACH 1.3-3 15/12/23 9:21 AM
34
Teaching Tip
Be sure students understand the difference
between the terms agonist and antagonist
as they pertain to drugs. Being able to
differentiate between the terms will help
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students on the AP exam.
07/02/24 5:18 PM