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Retronasal Olfaction
Published in Alan R. Hirsch, Nutrition and Sensation, 2023
Jason J. Gruss, Alan R. Hirsch
The olfactory bulb has two main connections. First, it is linked directly to the primary olfactory cortex. This is unique. All other sensory modalities route through the thalamus. The primary olfactory cortex is found at the junction of the anterior-medial temporal lobe and the ventral-posterior frontal lobe. The primary olfactory cortex connects to several other cortical areas: thalamus, hypothalamus, amygdala, entorhinal cortex, and the first-degree gustatory cortex—explaining why food odors stimulate gustatory centers and thus influence taste perception (Boesveldt, Albrecht, Gerber, Negoias, Hummel, and Lundstrom 2010). Moreover, the orbital network in the prefrontal cortex integrates sensations of olfaction, gustation, visceral, visual, and somatosensory for judgment of food (Price 2008). However, the neuroanatomical structures activated varied, depending on route of odor presentation. Orthonasal olfaction preferentially enhanced discharge of the insula and amygdala whenever retronasal olfaction induced greater activation of the anterior cingulate cortex (Spetter, Bender, Hummel, Negoias, Veldhuizen, and Small 2011).
The nervous system
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
In addition to the somatosensory cortex, there are special senses areas in the cerebral cortex involved with the primary or initial processing of a specific type of stimulus. The primary visual cortex (sight) is located within the occipital lobes, the primary auditory cortex (hearing) and the primary olfactory cortex (smell) are found within the temporal lobes and the primary gustatory or taste cortex is located at the base of the somatosensory cortex in the parietal lobes.
The sense of smell in relation to our affective states and wellbeing
Published in Philip N. Murphy, The Routledge International Handbook of Psychobiology, 2018
C. Licon, C. Manesse, C. Rouby, M. Bensafi
It is due to its tight anatomical connections with brain areas also involved in emotional processing that the olfactory system is well positioned to influence affect, mood and emotions (Rouby, Pouliot, & Bensafi, 2009). Neurobiologically, any environmental volatile molecules with certain properties (appropriate polarity, water solubility, vapor pressure, etc.) have a chance of being detected and discriminated by olfactory receptors in the nasal cavity. The cilia (hair-cells) of sensory neurons are in direct contact with inhaled molecules, and contain olfactory receptors that bind to odorant molecules and initiate the neural message from the olfactory nerve to the olfactory bulb. Each olfactory cell expresses one of 350 receptor proteins that recognize certain molecular features of the odorant; the axons of cells bearing the same receptor type converge on the same glomerulus, a functional unit in the olfactory bulb, and thus represent the odorant’s chemical properties in a spatial map of the excitations and inhibitions of a combination of receptors (Firestein, 2001; Secundo, Snitz, & Sobel, 2014). The primary olfactory cortex, including the amygdala and piriform cortex in the temporal lobes, processes both the chemical and the affective properties of stimuli. The secondary cortex includes the insular and orbitofrontal cortices, where several representations of odors are constructed according to their pleasantness/unpleasantness and meaning for the perceiver in his/her actual situation, including internal states such as hunger and satiety (Gottfried, 2006; Yeshurun & Sobel, 2010).
Investigational drugs for the treatment of olfactory dysfunction
Published in Expert Opinion on Investigational Drugs, 2022
Arianna Di Stadio, Cinzia Severini, Andrea Colizza, Marco De Vincentiis, Ignazio La Mantia
The neuroepithelium is connected through the axons of the ORN to the olfactory bulb, which contains glomerulus, mitral cells and tufted relay neurons. The axons converge in the glomerulus to form the first cranial nerve (olfactory nerve). The glomerulus is connected by synapses to the mitral cells; the latter together with the tufted relay neurons forms the olfactory tract. This structure bifurcates in the medial and lateral olfactory stria (y inverted-shaped). The olfactory stimulus is conducted through these structures up to the piriform cortex, the periamygdaloid cortex, the olfactory tuberculosis and the anterior olfactory nucleus. The primary olfactory cortex is formed by the medial and lateral olfactory stria and the anterior perforated substance. The lateral olfactory stria is extended posteriorly giving origin to the entorhinal area which, together with the uncus, forms the secondary olfactory cortex, also known as the orbitofrontal cortex (Figure 2). This area is straightly related to memory. The primary cortex is responsible for the active perception of the sense of smell, while the secondary one is the portion where the smell perception is integrated with emotions and memory.
Clinicoradiological features in amyotrophic lateral sclerosis patients with olfactory dysfunction
Published in Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration, 2021
Michihito Masuda, Hirohisa Watanabe, Aya Ogura, Reiko Ohdake, Toshiyasu Kato, Kazuya Kawabata, Kazuhiro Hara, Ryoichi Nakamura, Naoki Atsuta, Bagarinao Epifanio, Masahisa Katsuno, Gen Sobue
The medial orbital cortex and hippocampus form part of the olfactory center (31,32). Olfactory stimuli from the primary olfactory cortex to the olfactory center, including the orbitofrontal cortex and the hippocampus, links odor inputs to systems that are associated with affective learning and memory (33–35). Previous neuroimaging studies have revealed orbital cortex and hippocampus were involved with olfactory dysfunction in other neurodegenerative diseases (6,36). In ALS, a postmortem neuropathological study has revealed TDP-43-positive inclusions in the prefrontal neocortex, including the orbital cortex and hippocampus (37). Takeda et al. (11) reported a possible expansion of TDP-43 pathology from the hippocampus, through the anterior olfactory nucleus, periamygdaloid complex, and piriform cortex, to the olfactory bulb and orbital cortex. They suggested that olfactory dysfunction in ALS patients may be a consequence of the disease expanding to the extra-motor system, mainly the olfactory center including orbitofrontal cortex and hippocampus.