Chemosensation Flashcards
Anosmia
Loss of smell
Aguesia
Loss of taste
What is the morphology of taste receptor cells?
Each taste bud consists of ~100 cells, about 50% of which are taste cells and 50% are glial cells
Taste cells have a limited lifespan and turn over every 10-30 days
What are the two pathways by which olfactory epithelium can be stimulated?
Orthonasally - by odorants entering the nostril
Retronasally - by odorants from substances in the mouth which curve backward past the soft palate and enter the nasal cavity from the rear
What information do the 4 taste sensations provide?
Taste provides information about the chemical composition of food, including:
Salt (salt taste) Carbohydrates (sweet) Protein (umami) pH (sour) Toxins (bitter)
What are the 3 types of taste papillae?
Fungiform (anterior 2/3 of tongue)
Foliate (sides of tongue)
Circumvallate (posterior 1/3 of tongue)
What is the innervation pathway of the anterior 2/3 of the tongue?
Fungiform and foliate papillae in the anterior 2/3 of the tongue are contacted by the chorda tympani branch of VII (traveling with the lingual n.)
Circumvallate papillae in the posterior 1/3 of the tongue are contacted by CN IX and taste cells of the pharynx are contacted by branches of X
Taste afferents converge on the nucleus of the solitary tract
What is the role of ATP in taste signaling?
ATP acting on neural P2X receptors is strongly involved in transmission of taste information; analgesics which block P2X receptors can cause lost of taste
What are 2 examples of the impact of genetic polymorphisms in taste receptors on individual health?
Individuals with greater sensitivity to bitter taste (i.e. PROP tasters) consume fewer vegetables and have higher incidence of nutrition-related disease
Airway epithelial cells express “bitter” taste receptors to detect bacterial signaling molecules; PROP non-tasters have higher incidence of respiratory bacterial disease
What is the morphology of olfactory receptor cells?
Olfactory neurons within the olfactory neuroepithelium extend cilia into the mucus layer to contact odorants dissolved in the mucus layer; olfactory neurons are bipolar and the afferent axons (CN I) run into the olfactory bulb of the CNS where they synapse on glomeruli
Describe signal transduction in the olfactory receptor cell
Binding of an odorant to its receptor activates adenylate cyclase to produce cAMP; cAMP opens gated Na+/Ca2+ channels; the influx of Ca2+ opens gated Cl- channels which allow Cl- efflux from the cell, causing depolariation
What is the role of the orbitofrontal cortex? Where does it’s input come from?
Orbitofrontal cortex receives input from the gustatory system via the insular cortex, as well as from the olfactory system via piriform olfactory cortex
Where does the olfactory project to?
The olfactory tract projects to different regions of the olfactory cortex; these different regions of olfactory cortex project to secondary olfactory processing regions, i.e. orbitofrontal cortex (integration with gustatory information to produce taste), hippocampus (memory), and hypothalamus (homeostasis)
