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Olfaction

Olfaction

The sense of smell is achieved through the activities of the olfactory system. It starts when an airborne odorant enters the nasal cavity and reaches olfactory epithelium (OE). The OE is protected by a thin layer of mucus, which also serves the purpose of dissolving more complex compounds into simpler chemical odorants. The size of the OE and the density of sensory neurons varies among species; in humans, the OE is only about 9-10 cm2.
The olfactory receptors are embedded in the cilia of the...

Olfactory Receptors: Location and Structure

Olfactory Receptors: Location and Structure

The process of olfaction, also known as the sense of smell, is a sophisticated chemical response system. The specialized sensory neurons that facilitate this process, known as olfactory receptor neurons, are situated in an upper segment of the nasal cavity, known as the olfactory epithelium. Olfactory sensory neurons are bipolar, with their dendrites extending from the epithelium's apex into the mucus that lines the nasal cavity. Airborne molecules, when inhaled, traverse the olfactory...

Physiology of Smell and Olfactory Pathway

Physiology of Smell and Olfactory Pathway

Humans detect odors with the help of specialized cells located in the upper part of the nasal cavity, called olfactory receptor neurons (ORNs). ORNs possess hair-like structures called cilia, which are receptive to sensations from the inhaled air. When an odorant molecule binds to a specific receptor on the cell of the cilia, it leads to a series of events that ultimately cause the ORN to send electrical signals to the olfactory bulb in the brain through the olfactory nerves.
The olfactory...

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Related Experiment Video

Updated: Sep 28, 2025

Simple and Computer-assisted Olfactory Testing for Mice

Simple and Computer-assisted Olfactory Testing for Mice

Published on: June 15, 2015

Olfactory function and discrimination ability in the elderly: a pilot study.

Sae Uchida¹, Chiho Shimada^2,3, Naoko Sakuma⁴

¹Department of Autonomic Neuroscience, Tokyo Metropolitan Institute of Gerontology, 35-2 Sakaecho, Itabashi-ku, Tokyo, 173-0015, Japan. suchida@tmig.or.jp.

The Journal of Physiological Sciences : JPS

|April 2, 2022

Summary

This summary is machine-generated.

Older adults with poorer smell identification ability experienced a greater decline in odor discrimination. This suggests a link between olfactory impairment and cognitive decline, potentially involving the cholinergic system.

Keywords:

Cholinergic system Cognitive function Discrimination ability Elderly people Odor identification threshold Olfactory function

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Last Updated: Sep 28, 2025

Simple and Computer-assisted Olfactory Testing for Mice

Simple and Computer-assisted Olfactory Testing for Mice

Published on: June 15, 2015

Olfactory Context Dependent Memory: Direct Presentation of Odorants

Olfactory Context Dependent Memory: Direct Presentation of Odorants

Published on: September 18, 2018

A Free-breathing fMRI Method to Study Human Olfactory Function

A Free-breathing fMRI Method to Study Human Olfactory Function

Published on: July 30, 2017

Area of Science:

Neuroscience
Gerontology
Olfactory Research

Background:

Previous research indicated a link between higher olfactory identification thresholds and reduced attentional ability in the elderly.
Olfactory dysfunction is increasingly recognized as a potential early indicator of cognitive decline.

Purpose of the Study:

To investigate the relationship between olfactory identification threshold and odor discrimination ability in elderly individuals.
To explore the potential connection between olfactory impairment and cognitive function decline in aging.

Main Methods:

Assessed olfactory function using the rose odor identification threshold in 12 community-dwelling elderly subjects (mean age 80.9 years).
Evaluated odor discrimination ability by having participants distinguish between 5 similar odor pairs.

Main Results:

Subjects with a higher olfactory identification threshold (≥5) showed a significant decline in odor discrimination ability (14% ± 14%, p=0.03).
This decline was compared to individuals with lower thresholds (≤4), who maintained their discrimination ability (set at 100% average).

Conclusions:

Olfactory impairment, specifically a higher identification threshold, is associated with reduced odor discrimination in the elderly.
Given that discrimination ability is linked to the basal forebrain cholinergic system, these findings suggest olfactory dysfunction may be connected to cognitive decline involving this system.