PSY333H5 Lecture Notes - Lecture 7: Posterior Grey Column, Dorsal Root Ganglion, Spinothalamic Tract

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Published on 1 Aug 2012
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PSY333 FINAL MATERIAL !
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PSY333 LECTURE 7!
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Pain...!
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pain= syptom of chief concern to paitents!
- leads them to seek medical attention!
- pain is secondary for the physician they want to find out what the underlying causes for the symptom are. !
- Patients fear pain in illness and treatment most!
- Fearing that they can't relieve suffering --> inc anxiety!
- most common reason for euthanasia (youth in asia) !
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4 billion dollars spent annually in Canada on over the counter pain meds !
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- pain is adaptive!
- tells us to avoid behaviours that may hurt us!
- Forces us to rest and recover after an injury !
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can be reflexive and unconschious !
- hot stove burner !
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Operant conditioning!
- learning based on consequences!
- positive = add, negative = take away !
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Reinforcement: consequence increases likelihood of behaviour in future reinforcement increasest behaviur !
- Positive reinforcement- application of a desirable stimulus (reward; candy)!
- negative reinforcement - removal of a negative stimulus ( don't have to do chore if good) !
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punishment: consequence decrease likelihood of behaviour in future punishment decreases behaviour !
- Positive punsihment- application of aversive stimulus (spanking)!
- Negative punishment - take away something good (t.v time)!
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Using pain to learn !
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positive punishment negative reinforcement !
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involves aversive, potentially painful stimuli!
- electric shock!
- spanking!
- soothing burn !
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Pain behaviours are behaviours that occur in response to pain such as !
1. facial and audible expressions of diestress!
2. distortions in posture or gait!
3. negative affect!
4. avoidance of activity !
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Pain is subjective experience!
- degree to which pain is felt and how incapacitating it is depends on how it is interpreted. !
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What is pain: elusive nature!
- pain is subjective experience!
- degree to which pain is felt and how incapacitating it is depneds on how it is interpreted!
- heavily influenced by context in which it is experienced!
- Beecher's example of soldiers vs. civilians!
- 25% of wounded soldiers ask for morphine vs 80% of civilians after surgery!
- what is pain for the soldier !
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- Sports injury continue to play!
SNS arousal diminishes pain sensitivity !
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Can refer to many different sensations!
- Sharp pain!
- Dull ache!
- Blistering!
- Small but irritating !
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Acute Pain!
- Intense!
- Short lived!
- disappears as injury heals!
- < 6 months !
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Chronic Pain !
- Begins as acute pain!
- doesn't go away!
lower back pain, headaches, arthrities!
recurrent intracttable benign vs. progressive !
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WHAT IS PAIN!
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Pain (Operational definition): an unpleasant sensory and emotional experience associated with actual or potential tissue damare,
or described in terms of such damage. !
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Pain physiology!
- Despite enormous variability in how we perceive pain there is an innate and hard-wired physiological basis for pain!
- overview:!
- Free nerve endings in peripher!
- send mesages to spinal cord!
-spinal tracts carry messages to midbrain & thalamus!
- conscious attention in brain !
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Nociception!
- contact with stimulus - stimuli can be mechanical (pressure, punctures and cuts) or chemical (burns).!
- reception-- A nerve ending senses the stimulus !
- transmission: a nerve sens the signal to the central nervous system. the relay of information usually involves several neurons
within the CNS!
- Pain center reception the brain receives the signal and interprets it !
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3 kinds of pain perceptions (nociception!
mechanical, thermal, chemical!
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differences in types of pain attributed to differnces in pain receptors (nociceptors) !
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unevenly distributed in body, i.e no pain receptors within brain. !
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Location: any area of the body that can sense pain either internally or externally!
- external: skin, cornea and mucosa!
- internal: muscles, joings, bladder, gut !
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Thermal nocicptors activatied by noxious heat or cold at various temps!
Mechanical nociceptors respon to excess pressure or mechanical deformation (incision)!
Chemical Nociceptors: respont to spices capsaicin and chemical agents!
polymodal respond ot more than one of these modalities !
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!
2 different types of axons: !
A delta fibers axons;!
- myelinated!
- action potentials travel at 20 m/s !
- Sharp pain!
- Thermal and mechanical !
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C fiber axons!
- unmeylinated!
- action potentials trave slow!
- dull and aching pain!
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Nociceptors!
- axons extend into peripheral nerovus sytem (PNS)!
- cell bodies located in dorsal root ganglia of spinal cord!
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Pain Pathway!
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- Peripheral nerves (first order neurons) enter spinal cord at dorsal horn!
- dorsal horn divided intor distinct layers (laminae)!
- A delta fibers connect lamina I and V!
- C fibers connect with lamina II !
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In spinal cord, first order neurons project to second order neruons and cross midline to ascend spine !
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Pain Pathway!
3 pain tracts!
- spinothalamic!
- spinoreticular!
- spinomesencephalic!
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Sensory aspects of pain!
- A delta fibers - project onto thalamus & sensory areas of cerebral cortex!
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Motivational/ affective aspects!
- C fibers - thalamic hypothalamic, cerebral cortex areas !
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The brain can influence pain perception!
- the pain form the cut on your hand eventually subsides or reduces to a lower intensity!
- If you consciously distract yourself, you dont think about the pain and it bothers you less!
- people given placebos for pain control often report that pain ceases or diminishes !
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- Ascending pathway to brain initiates conscious realization of pain!
- descending pathway from brain modulates pain sensory!
- sensations modulated at dorsal horn !
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Opiods stop pain by stoping message from first order neuron from getting to second order neuron. second order neuron not
activated and then message never ends up leaving the dorsal horn. descending pathway is more than a pshysiological system!
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Despite clear physiological role for pain, we know psychosocial factors also produce pain!
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Up to 85% of back pain complaints don't have a clear physical basis. !
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Variables contributing to pain perception!
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STRESS!
- Sternbach (1986): headaches in low stressed (7%) vs. moderate stress (17%) vs. highly stressed (25%) !
- Geil et al (2004): more stress on a given day report increased pain on that day and increased use of health care (hospitals, ER
visits, calls to doctors, medications) !
- Walker et al (2001): children with recurrent abdominal pain report more stress !
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Document Summary

Pain pain= syptom of chief concern to paitents. Pain is secondary for the physician they want to nd out what the underlying causes for the symptom are. Patients fear pain in illness and treatment most. Fearing that they can"t relieve suffering --> inc anxiety. Most common reason for euthanasia (youth in asia) 4 billion dollars spent annually in canada on over the counter pain meds. Tells us to avoid behaviours that may hurt us. Forces us to rest and recover after an injury can be re exive and unconschious. Positive = add, negative = take away. Reinforcement: consequence increases likelihood of behaviour in future reinforcement increasest behaviur. Positive reinforcement- application of a desirable stimulus (reward; candy) Negative reinforcement - removal of a negative stimulus ( don"t have to do chore if good) punishment: consequence decrease likelihood of behaviour in future punishment decreases behaviour. Positive punsihment- application of aversive stimulus (spanking) Negative punishment - take away something good (t. v time)

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