Signal transduction in nociceptors: general principles

Sensory transduction is the mechanism by which external physical changes are transformed into internal biochemical and/or electrical signals. Such electrical signals are propagated and processed through different levels of the central nervous system to elicit a sensation. Sensory transduction takes place in specialized portions of sensory receptor cells (sensory receptors), which differ from each other in their ability to respond preferentially to a particular form of energy. In turn, sensory receptors of the same class are connected to the brain through specific sensory pathways, whose selective excitation leads to a given modality of sensation. The relationship between the activation of peripheral nociceptors and conscious sensations is complex. In strict terms, receptor cells found in living organisms detect the manifestations of just two of the four fundamental forces of the universe: the gravitational force and the electromagnetic force. The type of energy to which sensory cells are specifically tuned has been used as a criterion for their classification: chemoreceptors are excited by molecules of various types; temperature changes excite thermoreceptors; photons are selectively detected by photoreceptors while mechanoreceptors respond to mechanical energy.