**Author details**

*Sino-Nasal and Olfactory System Disorders*

**5. Olfaction and gustation**

importance of olfactory stimuli as social cues.

(NSF IOS-1355034) to Thomas Heinbockel.

**Acknowledgements**

**Conflict of interest**

of this chapter.

olfactory processing during different behavioral states.

can be encoded through a combination of olfactory receptors, where each olfactory receptor detects one molecular feature of the odorant. Mitral and tufted cells send their axons through the lateral olfactory tract to the olfactory cortex, which includes the anterior olfactory nucleus, the piriform cortex, parts of the amygdala, the olfactory tubercle, and parts of the entorhinal cortex. From the amygdala, olfactory information is passed on to the hypothalamus and from the entorhinal cortex to the hippocampus. Olfactory information can be sent to the orbitofrontal cortex through the thalamus from olfactory cortical areas, except the anterior olfactory nucleus. Centrifugal fibers that originate outside of the olfactory bulb project to the olfactory bulb from the basal forebrain (horizontal limb of the diagonal band) and midbrain (locus coeruleus and raphe). The functional significance is a possible modulation of

Olfactory disorders and dysfunctions have received attention because they can result in serious problems, such as our inability to smell warning odors (fire, gas) and an impaired ability to taste food through retronasal stimulation of olfactory receptors [3]. Anosmia (loss of smell) and hyposmia (diminished smell) result from a number of etiologies. Specific anosmia refers to lowered sensitivity to a specific odorant and general anosmia denotes complete lack of olfactory sensation. Dysosmia (distorted smell) and phantosmia (phantom smells) may accompany these conditions. Cacosmia refers to olfactory hallucinations of repugnant smells.

Olfaction and gustation are our chemical senses and share a number of similarities and differences. Both senses extract information from the chemical stimuli in the environment, respond to a wide array of chemicals, and use G-protein-coupled receptors. However, in taste, this transduction mechanism is limited to sweet, bitter, and umami, whereas salty and sour use other signaling mechanisms. Receptor cells in olfaction and gustation show strong adaptation during continued stimulation and they undergo turnover and replacement throughout life. Both chemical senses provide important information for our survival and play a role in food selection and protect us from ingesting toxins. One difference between the two sensory systems is the fact that olfactory receptor cells are neurons and taste receptor cells are modified epithelial cells. Our understanding of the coding of taste qualities is better than that of odor quality. While olfactory stimuli evoke many sensations, no clear odor qualities have been described. The success of the perfume industry tells about the

This work was supported in part by grants from the National Science Foundation

The authors declare that there is no conflict of interests regarding the publication

**6**

Thomas Heinbockel\* and Balwant S. Gendeh Department of Anatomy, Howard University College of Medicine, Washington, DC, USA

\*Address all correspondence to: theinbockel@howard.edu

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
