Post-COVID-19 persistent olfactory, gustatory, and trigeminal chemosensory disorders: Definitions, mechanisms, and potential treatments

Figure 3 The process of olfaction. The signaling cascade which converts chemical information of the odorant into electrical information includes activation of cyclic nucleotide-gated ion channel followed by activated ADCY3 to convert ATP to cyclic adenine monophosphate (cAMP). cAMP unfolds Ca⁺⁺ activated Cl^- channels, causing influx of Na⁺ and Ca⁺⁺ from outside to inside the olfactory sensory neurons, and this activates the Cl^- channels, causing outflow of Cl^-, neuronal membrane depolarization, and the action potential. The latter extends from the epithelium to the bulb and then to the olfactory cortex.