Nociception and Pain

04/12/2017

Pain has been defined by the International Association  for the Study of Pain in 2016 as ” an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or describe in terms of such damage” . Physiological pain is a body protective mechanism, in order to avoid injuries or tissue damage. Faced with tissue injuries pathological pain will provide the appropriate condition for the healing process.

Once installed the injury might come with the concept of pathological pain which, according to its origin, can be classified as nociceptive or neuropathic. Pain may also be classified according to the time the individual has been suffering from it as acute pain or chronic pain.

The physiological component of pain is called nociception, which entails the proccess of  neuronal transduction, synaptic transmission and modulation of neuronal signs generated as a response to an external noxious stimulus. In other words, it works as a three-neuron chain reaction, with first order neuron originating from the peripheral area and projecting itself towards the spinal chord, second order neuron ascends through the spinal chord and third order neuron projects itself to the cerebral cortex.

Resultado de imagem para first order neurons

The first stage of nociception is decoding the mechanic, thermal and chemical stimuli onto electrical impulses through specialized neuronal terminal known as nociceptors.

Resultado de imagem para nociception transduction modulation

O primeiro processo da nocicepção é a decodificação de sensações mecânica, térmica e química em impulsos elétricos por terminais nervosos especializados denominados nociceptores. Os nociceptores são terminações nervosas livres dos neurônios de primeira ordem, cuja função é preservar a homeostasia tecidual, assinalando uma injúria potencial ou real. Os neurônios de primeira ordem são classificados em três grandes grupos, segundo seu diâmetro, seu grau de mielinização e sua velocidade de condução: Fibras Aβ, Fibras Aδ e Fibras C. Uma vez instalado o estímulo nociceptivo, diversas alterações neuroendócrinas acontecem, promovendo um estado de hiperexcitabilidade do sistema nervoso central e periférico.