This physiological race depends on fiber diameter, insulation levels, and firing thresholds. The wide dynamic range neuron, identified experimentally by neurobiologist Lorne Mendell in 1966, receives both non-noxious mechanical inputs and severe nociceptive bombardment, balancing these opposing forces through physical summation.
| Nerve Fiber Type | Conduction Velocity | Myelination & Structure | Sensory Information Carried | Effect on the Spinal Gate |
|---|---|---|---|---|
| A-beta (Aβ) | 30, 70 m/s | Thick diameter, heavily myelinated | Touch, vibration, flutter, light pressure | Closes gate (excites inhibitory interneurons) |
| A-delta (Aδ) | 5, 30 m/s | Medium diameter, lightly myelinated | Sharp prickling, intense cold, acute trauma | Opens gate (drives transmission cells) |
| C fibers | 0.5, 2 m/s | Smallest diameter, completely unmyelinated | Dull aching, burning, lingering inflammation | Opens gate (inhibits interneuron braking) |
When you aggressively rub an injured elbow, you orchestrate tactile induced analgesia. The fast A-beta traffic floods the wide dynamic range neuron, triggering local interneurons to release pre-synaptic inhibitors. These chemical brakes cap the volume of incoming C-fiber discharges. The resulting signal arriving at the thalamus and somatosensory cortex registers as a mild pressure wave rather than an agonizing spike.
