Olfactory and Vomeronasal Systems Lecture Review

Flashcards covering key vocabulary related to the olfactory and vomeronasal sensory systems, based on lecture notes.

Chemical senses

A category of senses that includes smell, detecting chemical stimuli.

Anosmia

The inability to detect one or more odors, which can be genetic, acquired, or due to illness/injury.

Olfaction

The process of detecting airborne chemical stimuli called odorants, which are then encoded into electrical signals.

Odorants

Airborne chemical stimuli that are detected by the olfactory system.

Pheromones

Chemical secretions perceived by another animal as a communication strategy, often influencing reproductive or social behaviors.

Olfactory system

The sensory system responsible for the sense of smell, considered the 'oldest' or 'most primitive' sense.

Olfactory receptor neurons (ORNs)

Bipolar neurons located in the olfactory epithelium that interact with odorants and are the primary site of odorant transduction.

Olfactory epithelium

A sheet of neurons and supporting cells lining approximately half of the nasal cavity, where olfactory transduction begins.

Cribriform plate

A thin, perforated region of the skull that separates the olfactory epithelium from the brain, through which ORN axons project.

Olfactory bulb

A forebrain structure that receives direct projections from ORN axons and sends projections to the pyriform cortex and other forebrain structures.

Pyriform cortex

A 3-layered archicortex dedicated to olfaction, which receives direct projections from the olfactory bulb.

Thalamic relay (olfaction)

A unique characteristic of the olfactory system, as it does not include a direct thalamic relay from primary receptors to the cortical region for initial sensory processing.

Archicortex

A primitive, three-layered cortical structure, exemplified by the pyriform cortex, specialized for olfaction.

Olfactory acuity

The sharpness or keenness of the sense of smell, which is less acute in humans compared to many animals.

Detection threshold (olfaction)

The concentration level at which the presence of an odorant can be correctly identified above a chance level (50%).

Enantiomers

Mirror-image molecules that, despite similar chemical structures, can elicit different odor perceptions.

Respiratory epithelium

The lining of the nasal cavity that maintains appropriate temperature and moisture for inhaled air and provides an immune barrier.

Bowman's glands

Glands within the olfactory epithelium that secrete the protective mucus layer.

Mucus layer (olfactory)

A fluid layer secreted by Bowman's glands that protects exposed cells, controls the ionic milieu for cilia, and facilitates odorant binding.

Olfactory cilia

Hair-like extensions on the apical surface of ORNs that project into the mucus layer and are the primary site of odorant transduction.

Basal cells (olfactory)

Stem cells located in the olfactory epithelium that continuously regenerate new olfactory receptor neurons throughout life.

Sustentacular (supporting) cells

Cells within the olfactory epithelium that detoxify potentially dangerous chemicals and provide support to ORNs.

Neurogenesis (olfactory)

The continuous regeneration of olfactory neurons from basal stem cells, occurring every 6-8 weeks in rodents.

ACE-2 receptors

Receptors expressed by sustenacular cells that SARS-CoV2 can bind to, leading to infection and potentially anosmia in COVID-19.

Odorant receptor proteins

Specific proteins concentrated on the external surface of olfactory cilia to which odorants bind, initiating the transduction process.

Receptor potentials (olfactory)

The electrical response (depolarization) elicited in an ORN when odorants bind to its cilia.

Metabotropic receptors

A type of G protein-coupled receptor (GPCR) that olfactory odorant receptors belong to, initiating an intracellular signaling cascade upon activation.

Golf alpha subunit

A specific G-protein subunit that dissociates from metabotropic receptors upon odorant binding, activating adenyl cyclase III (ACIII).

Adenyl cyclase III (ACIII)

An enzyme activated by the Golf alpha subunit, leading to an increase in intracellular cyclic AMP (cAMP).

cAMP (cyclic AMP)

A second messenger molecule whose increased levels in ORNs cause the opening of Na+ and Ca2+ channels, leading to depolarization.

Depolarization (olfactory ORN)

The influx of positive ions (Na+, Ca2+), amplified by a Cl- current, into an ORN, creating a graded potential that can lead to an action potential.

Action potential (olfactory)

Electrical signals generated at the axon hillock of ORNs via voltage-gated Na+ channels and transmitted to the olfactory bulb.

Broadly tuned responses (ORNs)

The characteristic of most individual ORNs to respond to a variety of different odorants, indicating non-specific sensitivity to subsets of stimuli.

7-transmembrane GPCRs

The structural classification of odor receptors, meaning they span the cell membrane seven times and are coupled to G-proteins.

Olfactory nerve (Cranial Nerve I)

A large number of bundles formed by the axons of olfactory receptor neurons that project to the olfactory bulb.

Ipsilateral projection (olfaction)

The pathway where each olfactory nerve projects to the olfactory bulb on the same side of the body.

Glomeruli (olfactory bulb)

Spherical structures within the olfactory bulb that serve as synaptic targets where ORN axons contact the apical dendrites of mitral and tufted cells.

Mitral cells

The principal projection neurons of the olfactory bulb, whose dendrites receive synaptic input from ORN axons within glomeruli.

Excitatory glutamatergic synapses

The type of chemical synapses occurring between ORN axons and mitral cell dendrites within the glomeruli.

Convergence (olfactory bulb)

The process where a large number of ORN axons (typically expressing the same receptor) synapse onto a smaller number of mitral cells in a single glomerulus, increasing sensitivity.

Granule cells (olfactory bulb)

Interneurons in the olfactory bulb that synapse on the basal dendrites of mitral cells, establishing local inhibitory circuits and participating in synaptic plasticity.

Sparse coding mechanism (olfactory)

A hypothesized mechanism where the olfactory system represents a mixture of odorants over a relatively small subset of glomeruli, cuing in on dominant chemicals.

Orbitofrontal cortex (olfactory)

A higher brain region involved in reward processing, conscious appreciation of odors, and association of odors with other sensory characteristics, receiving projections from the pyriform cortex.

Vomeronasal system

A specialized chemosensory system, distinct from the main olfactory system, present in many animals (e.g., carnivores, rodents) for detecting airborne odors like pheromones and kairomones.

Accessory olfactory bulb (AOB)

A separate region of the olfactory bulb that processes sensory input specifically from the vomeronasal organ.