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Lecture 7

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Health Psychology- Lecture #7 Pain- Chapter 10 Intro: Pain can be an unconscious thought. You can use pain to learn experience Educating children (reinforcement technique) Chronic pain conditions**** (chronic back pain is the main type of pain) Significance of Pain • Pain= symptom of chief concern to patients - Leads them to seek medical attention • Pain often considered of secondary importance to MD (they want to understand what the underlying causes of the symptom are) • Patients fear pain in illness and treatment most - Fearing that they can’t relieve suffering  increase anxiety - Most common reason for euthanasia • $4 billion is spent annually in Canada on over-the-counter pain medications. Why do we feel pain? • Pain is adaptive - Tells us to avoid behaviours that may hurt us - Forces us to rest & recover after an injury • Can be reflexive and unconscious - Hot stove burner • Can be used as a learning mechanism - Electric shocks for rats - Spanking for children Pain as an inhibitory mechanism • Operant conditioning - Learning based on consequences - Positive= add; negative= take away • Reinforcement: consequence increases likelihood of behaviour in the future - Positive reinforcement- application of a desirable stimulus (reward; candy) - Negative reinforcement- removal of a negative stimulus (don’t have to do a chore if good) • Punishment: consequence decrease likelihood of behaviour in the future - Positive punishment- application of aversive stimulus (spanking) - Negative punishment- take away something good (TV time) • Using pain to learn • Positive punishment and negative reinforcement involve aversive, potentially painful stimuli - Electrical shock - Spanking - Soothing burns How do we know when someone is in pain? • Pain behaviours are behaviours that occur in response to pain such as 1. Facial & audible expressions of distress 2. Distortions in posture or gait 3. Negative affect 4. Avoidance of activity What is pain: elusive nature • Pain is a subjective experience - Degree to which pain is felt and how incapacitating it is depends on how it is interpreted • Heavily influence by context in which it is experienced - Beecher’s example of soldiers versus civilians  25% wounded soldiers ask for morphine versus 80% of civilians after surgery  Morphine is an objective measure of how much pain each group can withstand  What is pain for the soldier? For the patient?  Soldier’s feeling of pain was a symptom of survival; civilian was a symptom that something was wrong with their body. • Sports injury continue to play - Sympathetic nervous system arousal diminishes pain sensitivity What is pain? • Can refer to many different sensations - Sharp pain (step on a nail) - Dull ache (migraines) - Blistering (sunburn) - Small but irritating (paper cut) • Acute pain - Intense - Short-lived - Disappears as injury heals - <6 months • Chronic pain - Begins as acute pain - Doesn’t go away - E.g., lower-back pain, headaches, arthritis - Recurrent acute (comes again and again like a headache) vs. intractable- benign (doesn’t go away but not life threatening) vs. progressive (increases in intensity over time cancer) • Pain: an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Pain physiology • Despite enormous variability in how we perceive pain, there is an inane and hard- wired physiological basis for pain • Overview: - Free nerve endings in periphery - Send messages to spinal cord - Spinal tracts carry message to midbrain and thalamus - Conscious attention in brain 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 sends the signal to the central nervous system. The relay of information usually involves several neurons within the central nervous system. • Pain centre reception—the brain receives the information for further processing and action (can be conscious or unconscious). • 3 kinds of pain perceptions (nociception) - Mechanical (crushing, tearing, etc) - Thermal (heat or cold) - Chemical (iodine in a cut, tear gas) • Differences in types of pain attributed to differences in pain receptors (nociceptors) • Unevenly distributed in body - None in brain • Location: any area of the body that can sense pain either internally or externally - External: skin, cornea and mucous membranes - Internal: muscles, joints, bladder, gut Types of nociceptors • Classified based on which environmental modalities they respond to - Thermal nociceptors activated by noxious heat or cold at various temperatures - Mechanical nociceptors respond to excess pressure or mechanical deformation (incisions) - Chemical nociceptors respond to spices (capsaicin) and chemical agents (acrolein) - Polymodal nociceptors responds to more than one of these modalities • 2 different types of axons: • A-delta fibre axons - Myelinated - Action potentials travel at 20 meters/second - Sharp pain - Thermal and mechanical • C fibre axons - Unmyelinated - Action potentials travel at 2 meters/second - Dull or aching pain • Significance of myelination: increases speed of transmission, and so, sudden and intense pain is more rapidly conducted to cerebral cortex than is slower, dull, aching pain of C-fibres. • Axons extend into peripheral nervous system (PNS) • Cell bodies located in dorsal root ganglia of spinal cord Pain Pathway • Peripheral nerves (first order neurons) enter spinal cord at dorsal horn • Dorsal horn divided into distinct layers (laminae) - A-delta fibres connect to lamina I and V - C fibres connect with lamina II • In spinal cord, first order neurons project to second order neurons and cross midline to ascend spine • 3 pain tracts: - Spinothalamic - Spinoreticular - Spinomesencephalic - Wherever the termination is that is where the name comes from • Sensory aspects of pain - A-delta fibres—project onto thalamus and sensory areas of cerebral cortex • Motivational/affective aspects - C-fibres—thalamic, hypothalamic, cerebral cortex areas The brain can influence pain perception • The pain from the cut on your hand eventually subsides or reduces to a lower l et al (2intensity • If you consciously distract yourself, you don’t think about the pain and it bothers you less • People given placebos for pain control often report that the pain ceases or diminishes Descending pain pathway • Ascending pathway t
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