Psychology 2036A/B Chapter 8: Chapter 8 2036
17 Dec 2017
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Chapter 8
Pain "
Jake was a chef. One day cut up chicken and packaged them in freezer. Became ill from
salmonella; quarantined in the hospital where he spent 10 days and lost 30 pounds. "
Resumed activities- went back to work, played soccer but had new symptoms point pain,
urethritis (inflammed urethra), conjunctivitis (inflammed eye). Indicated by Reiters syndrome
(2-3% exposed to bacteria have it) "
Some recover within 6 months but Jake was unlucky he would eventually lose mobility. Made
career change so he could interact with others- bus driver "
Married had two children- years past pain increased. Couldn’t keep it together became
depressed and had anxiety attacks. Became suicidal, abused medication and alcohol so he
had to check into hospital where he would receive psychiatric help. Went to pain clinic and
learned management techniques and saw others that were worst off then him. "
Pain has affected him emotionally and physically. "
The Significance of Pain"
Miss. C’s father was a physician. Miss. C could not feel pain; bitten off tip of her tongue,
suffered third degree burns, could not remember sneezing or coughing, had no gag reflex or
corneal reflex that protects eyes. Caused medical issues. "
Melzack and Wall- insensitivity to pain can lead to people remaining in position too long
(inflamed joints) and neglect injuries. Died at 29 because infections could not be brought under
her control. "
Pain has survival value, prevents further injury, limits activity (enforcing rest) "
Pain Perception"
Person comes in contact with injurious stimuli, signals of tissue damage follow route from
afferent neutrons of PNS to spinal cord and brain. "
Afferent (sensory) neurons- nerve cells that conduct impulses from a sense organ to the CNS,
or from lower to higher levels in the spinal cord and brain "
Nociceptors- the afferent nerve endings that respond to pain stimuli "
-when activated nerve endings generate impulses that travel to the CNS. "
Afferent peripheral fibers that transmit pain pulses are A-delta fibres and C-fibres"
A-delta fibres- the afferent peripheral fibres that are associated with transmitting sharp, distinct
pain "
-small, myelinated fibres that transmit impulse quickly"
C- fibres- the afferent peripheral fibres that are associate with transmitting diffuse, dull or
aching pain "
-slower because unmyelinated "
Fibres bundle together leaving periphery and form nerves. Nerves enter dorsal horn of spinal
cord- contain layers/ laminae which receive messages "
Cells in first two layers are the substantia gelatinosa and modulate sensory input "
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A-fibres send messages through thalamus on way to cerebral cortex- signal sharp pain "
C- fibres send messages to brain stem and forebrain- motivational and affective elements of
pain"
Theories of Pain"
Gate Control Theory"
Melzack and Wall proposed "
Gare control theory- suggests that a neural mechanism in the dorsal horns of the spinal cord
acts like a gate that can increase or decrease the flow of nerve impulses from peripheral fibres
to the CNS, thereby influencing sensation of pain "
Introduced contribution of psych factors on pain - sensations modified as they are conducted
to brain by spinal cord "
Info enters dorsal horns via primary afferent neurons, info passed through substantia gelatinosa
where info is modulated by stimulation of periphery and feedback from fibres descending from
brain. Affects activity of transmission cells- conduct or not conduct pain sensation "
Pain affected by balance of activity in small and large nerve fibres. "
-activity of small A- delta and C- prolonged stimulation, opens gate, promotes sensitivity "
-Activity in large A- beta closes the gate "
Central control trigger- in the gate control theory of pain, a specialized system of large-
diameter, rapidly conducting fibres that activate selective cognitive processes that then
influence, by way of descending fibres, the opening and closing of the gate "
Pain influenced by past experience, attention and cognitive activities through central trigger
control - relaxation and positive experience can mute pain by causing gate to close"
Beecher- WW2- wound by civilian produces pain but same injury in soldier is less because
distracted by environment (gate closed) "
Suppressing pain allows one to defend themselves and escape further harm "
Injuries can go unnoticed if sensory input is heavily activated "
Not able to explain chronic pain problems like phantom limb pain "
Phantom Limb Pain- the experience of pain in an absent body part"
1866- Case of George Dedlow; lost arm and have both legs amputated- wakes up and asks
nurse to rub cramp in leg"
Phantom limb- limb that is very vivid to amputee, can usually tell you precise position. Behaves
like normal limb, moves in coordination with other limbs "
Sometimes convinced it is stuck in weird position- walked through door sideways cause arm
was sticking straight out of shoulder, slept on stomach cause arm was bend behind "
Phantom limb can experience sensations such as temp and pressure"
Limb can have lots of pain but restraint to treatment "
Cortical reorganization following amputation may cause phantom limb pain but others are born
without limbs and experience this "
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Neuromatrix Theory"
Neuromatrix theory- extension to gate theory, with greater emphasis placed on the brains role
in pain perception "
Genetically determined neuromatrix or network of brain neurons, generate patterns, process
info that flows through it and produces pattern that is felt as a whole body "
Patterns are neuro signature patterns- may be from sensory inputs or innately produced
(phantom limb) - produce multidimensional experience of pain "
Pain perception is part of complex process affected by sensory input, activity of NS and past
experiences "
Neurochemical Basis of Pain and Pain Inhibition
Gate theory- brain controls amount of pain by blocking transmission of pain signals "
David Reynolds- electrode in midbrain of rat. Clamped tail to produce pain. Rates with
electrode in midbrain did not exhibit pain "
Periaqueductal gray area- an area of the midbrain that is involved in pain reception "
Rat not feeling pain was called stimulation- produced analgesia (SPA)"
Stimulation- produced analgesia (SPA)- freedom from pain as a result of electrical stimulation"
Endogenous opioids- opiate like substances produced within the body that regulates pain "
-slowing or blocking transmission of nerve impulses "
Three main groups; beta-endorphin, proenkephalin and pro-dynorphin "
Pain and emotions are closely linked and studies found psych stress can trigger opioid activity "
Acute Versus Chronic Pain"
Case- "
Riley is 28 and finished residency in anesthesiology. Invited to high school reunion. Played
football scrimmage with old friends. Flew home and experienced sharp pain in back. Overdone
it in scrimmage and was going to be stiff. "
Michelle is professional pairs figure skater for 20 years. Decided to quit because of pain. Found
it harder to land jumps as she experience sharp pains in her knees. After each practice she
must ice her knee to help alleviate the pain. Also having difficulty simply walking. Likely
Michelle will be diagnosed with osteoarthritis. "
Acute Pain- pain that lasts less than 6 months and serves to warn of impending tissue damage
or the need for convalescent test"
-Rileys pain is acute because it is temporary; toothache, child birth, broken limb"
Chronic Pain- pain lasting for linger than 6 months "
-continues beyond healing and disrupts sleep and normal living "
-Michelle and Jake (from opening) have chronic pain "
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