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Module 1.6d

Biological Influences
Pain is a physical event produced by your senses. But pain differs from some of your other
sensations. No one type of stimulus triggers pain the way that light triggers vision. And no
specialized receptors process pain signals the way that your retina receptors react to light PRACTICE
rays. Instead, sensory receptors called nociceptors — mostly in your skin, but also in your
muscles and organs — detect harmful temperatures, pressure, or chemicals (Figure 1.6-23).
Research Methods & Design
(SP 2)
Figure 1.6-23 (10 minutes) Point out to your stu-
The pain circuit dents that the gate-control theory of
Sensory receptors (nociceptors) pain helps explain why people aren’t
respond to potentially damaging
stimuli by sending an impulse to always aware of pain. Pain signals
the spinal cord, which passes
the message to the brain, which can be controlled by the brain, which
interprets the signal as pain.
can choose which pain to consider
and which to ignore by blocking
Projection
to brain off pain signals in the spinal cord.
Research indicates that when surgical
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
Cross section of
Pain the spinal cord patients were told what to expect fol-
impulse
lowing surgery and to relax to reduce
Cell body of their pain, they needed fewer pain-
Copyright © Bedford, Freeman & Worth Publishers.
nociceptor
killers and were sent home 2.7 days
earlier than a control group. There is
Nerve
cell
more to pain than what stimulates the
sense receptors. Use this example to
review control groups and experimen-
Tissue
injury tal groups with students. Ask them
the following question: Why are con-
trol groups important in experiments?
Your pain experience depends in part on the genes you inherited and on your physical
characteristics (Gatchel et al., 2007; Reimann et al., 2010). Women are more sensitive to pain (The control group is the group not
than men are (their senses of hearing and smell also tend to be more sensitive) (Ruau et al., exposed to the treatment. It contrasts
2012; Wickelgren, 2009). with the experimental group and
No pain theory can explain all findings from research on pain. One useful model,
gate-control theory, suggests that the spinal cord contains a neurological “gate” that con- serves as a comparison for evaluating
trols the transmission of pain messages to the brain (Melzack & Katz, 2013; Melzack & Wall, the effect of the treatment.)
1965, 1983). gate-control theory the theory
Small spinal cord nerve fibers conduct most pain signals. An injury activates the small that the spinal cord contains a
fibers and opens the gate. The pain signals can then travel to your brain, and you feel pain. neurological “gate” that blocks
But large-fiber activity (stimulated by massage, electrical stimulation, or acupuncture) can pain signals or allows them to
close the pain gate by blocking pain signals. Brain-to-spinal-cord messages can also close pass on to the brain. The “gate” TEACH 1.6-13
the gate. Thus, chronic pain can be treated both by gate-closing stimulation, such as mas- is opened by the activity of pain
sage, and by mental activity, such as distraction (Wall, 2000). signals traveling up small nerve Enrichment
fibers, and is closed by activity
We also benefit from our own natural painkillers, endorphins, which are released in in larger fibers or by information
response to severe pain or vigorous exercise. People who carry a gene that boosts the avail- coming from the brain. Explain to your students that the
ability of endorphins are less bothered by pain, and their brain is less responsive to pain gate-control theory of pain may explain
why acupuncture works. Acupuncture is
Sensation: Skin, Chemical, and Body Senses and Sensory Interaction Module 1.6d 145 the ancient Chinese practice of inserting
needles into the skin at certain points to
alleviate pain. This practice may work
CONNECT 1.6-13
03_myersAPpsychology4e_28116_ch01_002_163.indd 145 15/12/23 9:26 AM because the needles create a competing
sensation that blocks the pain signals.
Refer students to the discussion of endor- The brain could also be releasing endor-
phins, the body’s natural painkillers, in phins to counteract the numerous pain
Module 1.3a. These endogenous morphines sensations that acupuncture creates,
work to alleviate pain and inhibit substance P, thereby alleviating pain.
the body’s pain neurotransmitter.

Sensation: Skin, Chemical, and Body Senses and Sensory Interaction Module 1.6d 145

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