The terminals of sensory nerves express specialized molecules that transduce the energy of mechanical, thermal, or chemical stimuli into electrical signals, which may trigger one or several action potentials. These action potentials will propagate along the axon and cause transmitter release at the synapse with second order neurons, thereby initiating central processing of sensory information that may ultimately lead to conscious perception (Fig. 1). Studies performed in vivo and in vitro have demonstrated a significant plasticity of primary sensory neurons, which contributes to the development of hyperalgesia (peripheral sensitization) (1-5). This chapter will describe mechanisms of peripheral sensitization based on the functionally distinct steps from the stimulus-induced depolarization of the nerve terminal to the transmitter release at the presynaptic ending.
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