Figure 1.
(a) The gate control mechanism proposed by Melzack and Wall in 1965. Both nociceptive and mechanoreceptors signals are projected to neurons in the substantia gelatinosa, represented by neuron 1, and towards the first central transmission neurons, represented by neuron 2. Mechanoreceptor signals are more intense (higher transmission rate) than nociceptive signals. Nociceptive signals inhibit neuron 1 (white dotted connection in figure) and, at the same time, produce excitation on neuron 2. (b) Current proposal: all nociceptive and mechanoreceptor axon terminals are excitatory. Synaptic weights (w i) change according to NMDA plasticity. Firing thresholds, t 1 and t 2, of neurons 1 and 2 also vary according to intrinsic plasticity.