What happens centrally in the spinal cord after tissue injury?
Tissue injury and inflammation result in locally released ligands that stimulate nociceptors and cause a barrage of electrical impulses from the primary afferent.
Substance P, CGRP, and glutamate are released at the central nerve terminal of the primary afferent.
These excitatory neurotransmitters trigger depolarization of the second-order neuron.
Repeated depolarization activates G-protein-related second messengers, inducing a phosphorylation cascade and activation of transcription factors.
The nerve may then upregulate its permeability to sodium and calcium and incorporate more ion channels in its membrane.
Thus, the neuron becomes more sensitized to the incoming traffic of impulses.