Olfaction Process and Olfactory Pathway

Study Notes

Olfactory System

Each glomerulus receives input from only one type of receptor cells, creating a map of odor information in the olfactory bulb.
Odorant signals are segregated into broad categories, independent of strength and interference from other odorants.
Each type of receptor corresponds to a distinct subset of glomeruli, and when an odorant binds to its receptor, it activates a specific pattern of glomeruli.

Glomeruli and Spatial Patterns

Individual glomeruli contain information from the same type of olfactory cell and receptor.
Differentially activated spatial responses are distinct for each odorant, reducing the response to different glomeruli.
Axons of each receptor type synapse to one glomerulus.

Temporal Patterns

The precise timing of action potentials in mitral and tufted cells relative to the inhalation cycle shapes the temporal dynamics of odorant coding.
Odorants evoke distinct patterns of neural activity across different phases of the inhalation cycle.

Receptor Types and Coupling

G-protein-coupled receptors (e.g., olfactory receptors) have long-lasting effects, signal amplification, and diverse postsynaptic actions, but are slower due to the signaling cascade.
Ion-channel-coupled receptors (e.g., photoreceptors) are faster but have limited control and diversity of postsynaptic actions.

Olfactory Receptor Activation

Odorants bind to membrane odorant receptor proteins, stimulating G-proteins, adenylyl cyclase, and cAMP, which opens cation channels and allows influx of Na+ and Ca2+.
This triggers a Cl- current, amplifying the olfactory receptor potential and causing membrane depolarization and action potential propagation.

Olfactory Epithelium and Olfactory Bulb

There are approximately 350 odorant receptor proteins in humans.
The olfactory epithelium is organized into zones, each containing a different subset of receptor cells, each expressing a single olfactory receptor protein.
Olfactory receptor neurons send axons into the two olfactory bulbs, with 2000 glomeruli in each bulb, and about 25,000 primary olfactory axons in each glomerulus.

Description

Test your understanding of the olfaction process, from the binding of odorants to olfactory receptor proteins to the transmission of signals through the olfactory bulb. Learn how cAMP and cation channels play a crucial role in amplifying the olfactory receptor potential.