Gate Control Theory of Pain

Overview

• Gate control theory: Transmission of pain signals is modulated at the spinal cord by non-painful inputs and descending signals from the brain.
• Non-painful inputs: Can "close the gate" to painful inputs, reducing pain signal transmission.

Pain Pathway

• Nociceptors: Pain receptors that are nerve endings of first-order neurons.
• Types of nerve fibers:
  • A-delta fibers: Fast, responsible for sharp pain.
  • C-fibers: Slow, responsible for dull, longer-lasting pain.

Signal Transmission

• First-order neurons: Travel via spinal nerves to the spinal cord and synapse with second-order neurons.
• Second-order neurons: Together with third-order neurons, carry pain signals to the brain.

Gate Mechanism

• Nerve gate location: Dorsal horn of the spinal cord.
• Function: Consists of interneurons that inhibit second-order neurons, stopping/reducing signal transmission.
  • Activation of nociceptors: Stimulates second-order neurons, inhibits inhibitory interneurons, opening the gate.
• Non-noxious stimuli: Activate large-diameter A-beta fibers, reactivating inhibitory neurons, stopping pain signals.
  • Examples: Touch, pressure, temperature changes.

Pain Treatment Techniques

• Skin rubbing, heat or cold packs: Relieve pain by activating non-nociceptive receptors.
• Transcutaneous nerve stimulation: Delivers electrical current to activate A-beta fibers and inhibit pain signals.

Brain's Role in Modulating Pain

• Endorphins: Morphine-like substances released by the brain in response to pain.
  • Effects:
    • Lowering pain perception by the brain.
    • Reducing pain signal transmission between first- and second-order neurons.
    • Mechanisms:
      • Preventing release of neurotransmitter substance P.
      • Inhibiting action potentials in postsynaptic neurons.
  • Induction factors: Pleasurable activities, excitement, meditation, laughter, vigorous exercise.
  • Effects: Underlies pain-relieving effects of exercise, positive state of mind.
    • Example: Athletes not feeling pain until after an event.