which change in an olfactory sensory neuron occurs when an odorant binds to a receptor?

The cellular and molecular machinery for olfactory transduction is located in the olfactory cilia (Figure 15.5B). Odorant transduction begins with odorant binding to specific receptors on the external surface of cilia. Binding may occur direct, or by manner of proteins in the mucus (chosen odorant bounden proteins) that sequester the odorant and shuttle information technology to the receptor. Several additional steps then generate a receptor potential by opening ion channels. In mammals, the primary pathway involves cyclic nucleotide-gated ion channels, similar to those found in rod photoreceptors (encounter Affiliate 11). The olfactory receptor neurons contain an olfactory-specific M-protein (G_olf), which activates an olfactory-specific adenylate cyclase (Figure xv.6A). The resulting increase in cyclic AMP (campsite) opens channels that allow Na⁺ and Caⁱⁱ⁺ entry (by and large Caⁱⁱ⁺), thus depolarizing the neuron. This depolarization, amplified past a Ca²⁺-activated Cl^- current, is conducted passively from the cilia to the axon hillock region of the olfactory receptor neuron, where activeness potentials are generated and transmitted to the olfactory seedling.

Figure xv.6

Olfactory transduction and olfactory receptor molecules. (A) Odorants in the mucus bind directly (or are shuttled via odorant binding proteins) to one of many receptor molecules located in the membranes of the cilia. This association activates an odorant-specific (more...)

Olfactory receptor neurons are especially efficient at extracting a bespeak from chemosensory noise. Fluctuations in the camp concentration in an olfactory receptor neuron could, in theory, crusade the receptor cell to be activated in the absenteeism of odorants. Such nonspecific responses practice not occur, yet, because the cAMP-gated channels are blocked at the resting potential by the high Caⁱⁱ⁺ and Mg²⁺ concentrations in mucus. To overcome this voltage-dependent cake, several channels must be opened at once. This requirement ensures that olfactory receptor neurons fire merely in response to stimulation by odorants. Moreover, changes in the odorant concentration change the latency of response, the elapsing of the response, and/or the firing frequency of individual neurons, each of which provides additional information nigh the environmental circumstances to the central stations in the system.

Finally, similar other sensory receptors, olfactory neurons adapt in the continued presence of a stimulus. Adaptation is apparent subjectively as a decreased power to place or discriminate odors during prolonged exposure (e.g., decreased awareness of being in a "smoking" room at a hotel as the minutes pass). Physiologically, olfactory receptor neurons indicate adaptation by a reduced rate of action potentials in response to the continued presence of an odorant. Accommodation occurs because of: (ane) increased Ca²⁺ bounden by calmodulin, which decreases the sensitivity of the channel to camp; and (two) the extrusion of Caⁱⁱ⁺ through the activation of Na⁺/Caⁱⁱ⁺ substitution proteins, which reduces the aamplitude of the receptor potential.

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