The Chemical Senses: Olfaction and Gustation — Vocabulary Flashcards

Vocabulary flashcards covering key terms from the lecture notes on smell (olfaction) and related olfactory processing.

Olfactory epithelium

Tissue in the nasal cavity that houses olfactory receptor neurons (ORNs), the site of primary olfactory transduction.

Olfactory receptor neuron (ORN)

Bipolar, unmyelinated sensory neuron in the olfactory epithelium that expresses a single odorant receptor gene and sends signals to the olfactory bulb.

Olfactory cilia

Specialized cilia on ORNs where odorant receptors are located and transduction occurs.

Bowman’s glands

Glands in the olfactory mucosa that secrete mucus to dissolve odorants and bring them to ORN cilia.

Odorant receptor (OR)

G-protein coupled receptor in ORNs that binds odorants in the cilia and activates intracellular signaling.

GPCRs as chemoreceptors

G-protein coupled receptors that detect chemical stimuli (odorants) and initiate intracellular signaling.

Adenylyl cyclase III (ACIII)

Enzyme activated by odorant receptor signaling to produce cAMP in ORNs.

Cyclic nucleotide-gated (CNG) channel

Ion channel opened by cAMP that depolarizes the ORN, triggering an action potential.

Cribriform plate

Bony barrier through which ORN axons pass from the nasal cavity to the olfactory bulb.

Olfactory bulb

Brain structure that receives input from ORNs via the olfactory tract and processes smell information.

Glomerulus (in the olfactory bulb)

Spherical structure where axons from ORNs expressing the same receptor converge; site of signal amplification.

Convergence on glomeruli

Pattern where ORN axons expressing the same receptor converge onto a single glomerulus to amplify signals.

Mitral cell

Principal output neuron of the olfactory bulb that transmits olfactory information to higher brain regions.

Across-fibre pattern coding

Odor identity is encoded by the spatial pattern of activity across many ORNs/glomeruli, not by a single receptor.

Olfactory receptor gene family

Large GPCR gene family (≈400 in humans, ≈1000 in dogs, ≈1200 in mice) encoding olfactory receptors.

One receptor gene per ORN

Each olfactory receptor neuron expresses only a single odorant receptor gene.

Olfactory receptor distribution in the nasal epithelium

Selective and regional distribution of different odorant receptor genes within the nasal epithelium.

Natural odors

Odors formed by mixtures of multiple odorant molecules; perception reflects the activated receptor pattern.

Threshold variability

Different odorants have different detection thresholds (e.g., ethanol vs. other compounds).

Piriform cortex

Primary olfactory cortex; major target of the lateral olfactory tract from the olfactory bulb.

Lateral olfactory tract

Pathway carrying olfactory information from the olfactory bulb to the piriform cortex and other regions.

Olfactory receptor gene expression per ORN

Each ORN expresses one receptor gene, but many ORNs share the same receptor type and project to the same glomerulus.

Olfactory transduction location

Odorant receptors located on olfactory cilia; activation leads to signaling that depolarizes the neuron.

Olfactory threshold example (ethanol)

Odor detection thresholds vary by molecule; ethanol example around 2 mM.

Indole as a natural odor example

Used to illustrate concentration dependence and pattern coding in olfactory processing.