Gate Control Theory of Pain

Overview

• Pain signal transmission can be modulated at the spinal cord level.
• Modulation occurs through non-painful inputs and descending signals from the brain.

Pain Signal Pathway

• Nociceptors: Pain receptors that are nerve endings of first-order neurons.
• Types of Nerve Fibers:
  • A-delta fibers: Fast fibers responsible for initial sharp pain.
  • C-fibers: Slow fibers responsible for dull, longer-lasting pain.
• Signal Transmission:
  • First-order neurons travel to the spinal cord via spinal nerves.
  • Synapse with second-order neurons, which with third-order neurons, carry signals to the brain.

Gate Control Mechanism

• Nerve Gate: Located in the dorsal horn of the spinal cord.
• Function: Controls pain signal passage to the brain.
• Interneurons: Inhibit second-order neurons to stop/reduce signal transmission.

Modulation of Pain Perception

• Activation of nociceptors opens the gate by inhibiting inhibitory interneurons, allowing pain signal transmission.
• Non-noxious stimuli (e.g., touch, pressure) activates large diameter Aβ fibers.
  • Reactivates inhibitory neurons, stopping pain transmission.

Applications

• Underlying mechanism for:
  • Skin rubbing
  • Heat or cold packs
  • Transcutaneous nerve stimulation: Small electrical current to activate non-nociceptive receptors.

Brain's Role in Pain Modulation

• Endorphins: Morphine-like substances released by the brain.
  • Reduce pain perception.
  • Inhibit pain signal transmission between first and second-order neurons.
  • Mechanisms:
    • Prevent release of neurotransmitter Substance P.
    • Inhibit postsynaptic neuron action potentials.

Factors Influencing Endorphin Production

• Pleasurable activities
• Excitement
• Meditation
• Laughter
• Vigorous exercise

Practical Implications

• Explains pain relief from physical exercise and positive mental states.
• Athletes often do not feel pain during competition due to endorphin release.