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. Author manuscript; available in PMC: 2015 Aug 1.
Published in final edited form as: Trends Neurosci. 2014 Jun 17;37(8):443–454. doi: 10.1016/j.tins.2014.05.005

Figure 1. Odorant concentration coding in olfactory sensory neurons (OSNs).

Figure 1

During sensory transduction (A), odorant molecules bind and stabilize the active states of olfactory receptors (R) in ciliary membranes of OSNs. The activated receptors (R*) couple to G-proteins (Golf) and increase synthesis of cyclic AMP (cAMP) by type III adenylyl cyclase (AC3). The cAMP opens cyclic nucleotide-gated channels that conduct calcium ions into the cilia and in turn open a channel (ANO2) mediating a depolarizing efflux of chloride ions. The resulting transduction current is passed to the OSN cell body where it drives a train of action potentials (spikes). The concentration of detected odorant is encoded non-linearly at each step of transduction: by a hyperbolic dependence on the number of activated receptors (R*) in the cilia (B), a strongly cooperative variation in amplitude of the transduction current (C), and similar sigmoidal variation of spike firing rate relayed by OSN axons (D). Data source: C, D: [115], normalized currents and firing rates of frog OSN response to cineole; mammalian OSNs exhibit similar dose-response profiles.