PSC 126 Lecture Notes - Lecture 15: Posterior Grey Column, Enkephalin, Endorphins
● The Gate Control Theory of Pain (Melzack & Wall, 1966)
○ There is a modulation of pain signals, before they reach the brain
■ “On” cells: A - delta, C fibers (normally dominate)
■ “Off” cells: A - beta
● Signals of pain are carried to the dorsal horn of the spinal cord & then to the brain
● Psychological processes determine how pain is perceived
○ Pain signal transmission is influenced by emotions & thoughts
○ Pain is less painful when we are distracted or involved in interesting activities
○ Pain is worse when we are anxious or depressed
○ Brain sends messages through descending fibers that stop, reduce, or amplify
pain signals
● What controls the opening & closing of the gate?
○ The amount of activity in the pain fibers (A - delta and C)
○ The amount of activity in other peripheral fibers (A - beta large diameter)
○ Messages that descend from the brain
● The gate control theory highlights the mind’s capacity to affect pain sensitivity
● Closing the gate: drugs block pain
○ Morphine shuts down the nociceptors (on - cells)
○ Endorphins & enkephalins: natural forms of morphine in the brain
○ Natural painkillers → block pain receptors
○ Released by brain → stimulate natural opiate receptors
● Pain, endorphins, and placebos
○ Pain → physio arousal
○ Pre - treated with morphine, no pain
○ Sequence is repeated
○ Then, placebo is administered
○ Placebo solution mimics the effect of morphine
● Can pain be reduced by thoughts ?
○ Endorphins and enkephalins
○ Brain chemicals released by expectations & beliefs block pain
○ Can be conditioned via the placebo effect
● But, what if receptors are blocked?
○ Naloxone: blocks the receptors for endorphins
■ Prevents the placebo
○ So, placebo has a real physical basis
● Depression and physical illness
○ The most common mental illness
○ Nearly 19 million Americans
○ 1 out of 5 have a lifetime risk
○ 15% on anti - depressants
○ 42% college students some symptoms/ 2 weeks
○ 80% of those with depression tend to develop physical health problems
○ Physical health problems can cause depression
Document Summary
The gate control theory of pain (melzack & wall, 1966) There is a modulation of pain signals, before they reach the brain. On cells: a - delta, c fibers (normally dominate) Signals of pain are carried to the dorsal horn of the spinal cord & then to the brain. Psychological processes determine how pain is perceived. Pain signal transmission is influenced by emotions & thoughts. Pain is less painful when we are distracted or involved in interesting activities. Pain is worse when we are anxious or depressed. Brain sends messages through descending fibers that stop, reduce, or amplify pain signals. The amount of activity in the pain fibers (a - delta and c) The amount of activity in other peripheral fibers (a - beta large diameter) The gate control theory highlights the mind"s capacity to affect pain sensitivity. Morphine shuts down the nociceptors (on - cells) Endorphins & enkephalins: natural forms of morphine in the brain.
