TRANSDUCTION OF OLFACTORY STIMULUS
The cilia membrane unfolds a tapestry adorned with G protein-coupled olfactory receptors, as depicted in the elegant tableau of Figure 12.3. The union of an odorant molecule with the receptor on the cilia sets in motion the activation of a G protein, known as Golf, forming a graceful partnership with guanosine triphosphate (GTP).
The ballet of transduction commences, guided by two distinguished second-messenger systems: inositol trisphosphate (IP3) and cyclic adenosine monophosphate (cAMP), elegantly portrayed in Figure 12.3. The GTP-Golf complex takes the lead, orchestrating a sequence of events. First, phospholipase C is activated, giving rise to IP3, which, in turn, opens Ca2+ channels. Simultaneously, adenylyl cyclase is stirred to action, producing cAMP, which unfurls Na+ and Ca2+ channels in the membrane, allowing for the graceful entry of Na+ and Ca2+ (primarily Ca2+), culminating in the subsequent depolarization of olfactory cells. This cascade of events, akin to a symphony, engenders excitatory postsynaptic graded potentials (EPSPs) within the cilia. Embarking on a journey, these ciliary EPSPs traverse from cilia to the trigger zone, the illustrious axon hillock, where their strength, when surpassing the threshold potential, begets the generation of action potentials. These action potentials, like heralds, traverse the axons of the olfactory cells, wending their way to the olfactory bulb. Herein lies the nexus from which impulses radiate, cascading through extensive realms of the central nervous system, a route to the piriform lobe, where the perception of smell takes its throne. A poetic uniqueness graces olfactory transmission - a swift adaptation to stimuli. An initial surge of axonal discharge in response to stimulation gracefully yields to a steady-state discharge of diminished amplitude, adding a nuanced cadence to the olfactory symphony (Figure 12.3).12.6
Source:
Rana Tanmoy (ed.). Principles of Veterinary Animal Physiology. CRC Press,2026. — 290 p.. 2026
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