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Retronasal Olfaction
Published in Alan R. Hirsch, Nutrition and Sensation, 2023
Jason J. Gruss, Alan R. Hirsch
Olfaction is the process by which chemical stimulants are processed into the sensation of smell. In this, aerosolized chemical stimulants traverse the nose, move into the olfactory cleft, and eventually contact the olfactory sensory neurons. With a sufficient stimulus, the sensory signal of smell is triggered. This is considered a chemosensory process, as the stimulus is a chemical that binds to a receptor. Most of the other human senses use different stimuli. Vision uses light; hearing uses sound waves; touch uses pressure. All of those sources are not from a chemical stimulus. Using chemicals to stimulate a response is known as chemosensation. Olfaction shares chemosensation with the sense of taste. Smell and taste are strongly linked in this regard. In fact, 90% of taste, or flavor, is actually smell (Hirsch 1992a). Despite the close association, there are significant differences between smell and taste.
Anatomy of the Respiratory Neural Network
Published in Susmita Chowdhuri, M Safwan Badr, James A Rowley, Control of Breathing during Sleep, 2022
Christopher A Del Negro, Christopher G Wilson
Respiratory rhythmic activity in pFV neurons goes away with age such that in adult rodents, the pFV neurons spike tonically without evidence of respiratory rhythmicity. Instead, their firing rate is modulated by pH and CO2 (145, 149). Nevertheless, even while embryonic Phox2b-expressing pFV neurons are respiratory rhythmic, their status as a central chemoreceptor is already well established (150). The mechanism of chemosensation depends on GPR4 receptors that bind protons and then regulate TASK2-type K+ channels (151, 152). KCNQ (i.e., KV7) type K+ channels also play a role in the chemosensory function of pFV neurons (153, 154).
Chemosensory Malingering
Published in Alan R. Hirsch, Neurological Malingering, 2018
The mechanism for such cooccurrence is not readily apparent. Possibly, this represents an abnormality in retronasal smell, gustatory response, or both. In classic first taste phenomena there may be rapid saturation whereas in temporal summation impairment of chemosensation may require a greater duration and intensity of sensory stimuli for taste to be perceived. Perhaps, dysfunctional sensory receptors involving strawberries require a greater or longer stimulation whereas receptors for other foods rapidly saturate. Conceivably, temporal summation is not due to the actual taste or smell of the food but rather due to memory filling the sensory lacunae. The tactile and masticatory experience of the food may provide a sensory illusion. This then complements the memory and creates an expectation effect with his past experience eating strawberries, and thus, is perceived as flavor. Consistent with his physical findings, both first taste and temporal summation indicate problems within the chemosensory system.
C. elegans: a sensible model for sensory biology
Published in Journal of Neurogenetics, 2020
Beyond mechanical stimuli, C. elegans also tastes and smells via multiple chemoreceptor families. Worm chemosensation has been studied extensively and the neural circuits and receptors responsible have been described in exquisite detail (Bargmann, 2006). Bargmann and colleagues led the identification of the large chemoreceptor family of G-protein couple receptors (GPCRs) with the discovery of the GPCR ODR-10 and its odorant ligand diacetyl (Sengupta, Chou, & Bargmann, 1996; Troemel, Chou, Dwyer, Colbert, & Bargmann, 1995). Of course, mammalian olfactory receptors are also known to be GPCRs (Buck & Axel, 1991). In addition, the transduction pathway is G protein signaling coupled to either cyclic nucleotide-gated (CNG) channels (TAX-4/TAX-2) or TRP channels (OSM-9/OCR-2 proteins). Both of these transduction mechanisms are also found in mammalian olfactory neurons. In addition to odorants and tastants, we now know that worms can detect a wide range of chemicals, including the physiologically relevant gases oxygen and carbon dioxide via a separate set of sensory neurons with guanylate cyclases as molecular sensors (Bargmann, 2006; Bretscher, Busch, & de Bono, 2008; Hallem & Sternberg, 2008). Worm sensory neurons also confer sensitivity to the pH and osmolarity of solutions (Bargmann, 2006; Wang, Li, Liu, Liu, & Xu, 2016), allowing worms to avoid harmful environments.
Intranasal trigeminal function in chronic rhinosinusitis: a review
Published in Expert Review of Clinical Immunology, 2023
Anna Kristina Hernandez, Thomas Hummel
Nasal chemosensation relies on the complex interaction of both the olfactory and trigeminal systems. The intranasal chemosensory trigeminal system is involved in the perception of odors, tactile sensation, temperature (heat, warmth, burning, cold, coolness, or freshness), respiration, and pain/tingling/stinging/irritation/pungency [1,2–6]. The trigeminal system plays a role as the sentinel of the respiratory system. It functions to protect the upper and lower airways from potentially harmful substances through physiologic reactions, such as: reflexive cessation of inhalation, subsequent expulsion or sneezing, and alteration of nasal congestion and secretions [4,7–10] (for extensive discussions on the anatomy and physiology of the trigeminal system, please see [8,11,12]).
A short guide to insect oviposition: when, where and how to lay an egg
Published in Journal of Neurogenetics, 2019
Kevin M. Cury, Benjamin Prud’homme, Nicolas Gompel
Chemosensation. The male ejaculate contains, in addition to spermatozoids, a fast evolving cocktail of hundreds of proteins, peptides and transcripts (e.g. Bono, Matzkin, Kelleher, & Markow, 2011; Findlay, Yi, Maccoss, & Swanson, 2008; Kelleher, Watts, LaFlamme, Haynes, & Markow, 2009), as well as pheromones (e.g. cis-vaccenyl acetate or cVA, Brieger & Butterworth, 1970). These molecules encompass a variety of functions meant to facilitate sperm transfer – including proteases, odorant binding proteins, and molecules involved in lipid metabolism – while a subset act as triggers capable of influencing the post-copulatory behavior of the female. The best characterized of these molecules, sex peptide (SP), was identified in Drosophila (Chen et al., 1988). It is not particularly well conserved across insects, but the study of its function offers an explicit framework to think of chemical triggers for post-mating responses. Upon transfer to the female, SP binds to sex peptide receptor (SPR) (Yapici et al., 2008), a receptor expressed in the female reproductive system, and modulates its signaling. Specifically, SPR is expressed and active in a handful of internal sensory neurons that innervate the female reproductive tract and its lumen (Hasemeyer, Yapici, Heberlein, & Dickson, 2009; Yang et al., 2009). These sensory neurons, genetically identified as expressing both the DEG/ENaC protein Pickpocket and transcripts of the sex-specific transcription factors fruitless (fru) and doublesex (dsx) (Hasemeyer et al., 2009; Rezával et al., 2012; Yang et al., 2009), are necessary and sufficient to mediate the post-mating state of a Drosophila female. Their projections to the abdominal ganglion are relayed to the higher brain (dorsal protocerebrum) by second-order neurons known as SAG (Feng, Palfreyman, Hasemeyer, Talsma, & Dickson, 2014). In short, SP binding to SPR in sensory neurons innervating the uterus reduces the activity of these neurons, which in turn lowers their activation of SAG neurons (Feng et al., 2014).