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Flashcards in chemosensation Deck (28)
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loss of taste



loss of smell


components of taste

olfaction (smell), gustation (taste proper) and chemesthesis (detection of irritant chemicals by trigeminal nerve endings).


For smell: list receptor cell, cranial nerve, primary sensory nucleus in CNS

ciliated, bipolar neuron receptor, cranial nerve I, olfactory bulb is sensory nucleus


For taste: list receptor cell, cranial nerve, primary sensory nucleus in CNS

Modified epithelial cell which synapses onto nerve fiber from cranial ganglion cell is receptor. CN VII, IX and X. Nucleus of solitary tract


For chemesthesis: list receptor cell, cranial nerve, primary sensory nucleus in CNS

Free nerve ending of cranial ganglion cell, CN V, spinal trigeminal nucleus


What are taste papillae and the types

Fungiform papillae are located all over the anterior end of the tongue, foliate papillae on the sides, and circumvallate papillae at the posterior part of the tongue


Which cranial nerves innervate each of the taste papillae

Fungiform: chorda tympani branch of facial nerve in anter 2/3 of tongue. Circumvallate: glossopharyngeal. Soft palate: superior petrosal branch of facial nerve. Posterior tongue, oropharynx and epiglottis: vagus


structure of taste buds

50-100 cells. Taste cells express taste receptor proteins and make contact with gustatory nerve fibers. They are replaced every 10-30 days by basal cells at bottom of taste bud.


Trace the neural pathways and name the central nuclei conveying taste information from taste buds to primary gustatory cortex.

taste bud > CN VIII, IX or X > synapse on second order neurons in rostral area of ipsilateral nucleus of solitary tract > second order cells send axons bilaterally to ventrobasal thalamus then taste cortex in insula (concious taste) OR second order cells send axons bilaterally to hypothalamus and amygdala (sub-concious reactions to taste)


Describe how variations in taste sensitivity to particular chemicals may relate to overall health status of individuals.

Individual differences in primary structure of the receptor proteins (polymorphisms) can lead to different degrees of sensitivity to particular taste substancesSuch differences in sensitivity may affect both diet and tolerance for bittertasting medicines. People with high sensitivity to bitter substances tend to eat fewer vegetables (e.g. broccoli is a bitter vegetable) and tend to have higher incidences of nutritionally-related disease, e.g. colonic neoplasms.


PROP detection and disease

Bitter taste receptors are expressed by epithelial cells of airway and respond to bacterial signaling. This same receptor detects PROP. People who are unable to detect PROP have higher incidence of respiratory bacterial disease b/c they are deficient at detecting and responding to airway bacteria


what type of receptors are the taste receptors that detect sour, salty, sweet, bitter and umami? Ion channel or GPCR

sour and salty: ion channel. Sweet, bitter, umami: G protein


olfactory system anatomy

olfactory neuroepithelium is covered with mucus. Olfactory neurons (olfactor receptor cells) extend thin processes called cilia into mucus layer. Odorants dissolve in the mucus and interact with olfactory receptor protins. Olfactory neurons are bipolar and they send a thin unmylinated axon towards olfactory bulb as part of the olfactory nerve


Unique property of olfactory neurons

they are the only neurons in the body that are continuously undergoing neurogensis and replacement. Basal cells under the epithelium serve as precursors. This occurs because olfactory neurons are exposed to the external environment and are subjected to attack by viruses, baceteria, etc. This property also makes them susceptible to cancer treatments


describe olfactory receptors

G protein linked. Subfamilies bind distinct structural classes of odor stimuli. Each olfactory receptor expresses one olfactory receptor protein.


Describe the way odor information is transmitted from the receptor epithelium to the olfactory bulb.

odorant binds olfactory receptor protein > activates G protein > adenylate cyclase activated > cAMP generated > cAMP opens channel allowing Na and Ca influx > Ca opens Cl channels > Cl flows out of receptor cell causing depolarization which travels from cilia to cell body >action potential in olfactor neuron is transmitted to olfactory bulb


structure of olfactory bulb

axons of olfactory neurons penetrate ethmoid bone and converge on glomeruli on the outer layer of the olfactory bulb. Each glomeruli has 1000 axons making excitatory synapses with apical dendrites of 2-25 mitral (or tufted) cells. Olfacory receptor neurons expressing th same olfactory protein project their axons to the same glomeruli.


How is odor quality encoded

through a odor-related map of glomeruli in olfactory bulb. In the olfactory epithelium, receptor cells with common receptors are spread throughout the epithelium, but in the olfactory bulb they converge onto the same glomeruli. Since each odorant can stimulate more than one receptor, it will be distributed in wide areas of glomerular layer, thus the recognition of that odordant depents on recognition of the pattern of activity across glomeruli


Pathway from olfactory bulb to cortex

The olfactory bulb projects directly to the cortex, unlike the other sensory systems which pass through the thalamus. Axons of output cells from bulb collect in the lateral olfactory tract and project directly to olfactory cortex and part of amygdala.


anatomy of olfactory cortex

consists of lateral olfactory gyrus and part of uncus. It is divided into piriform cortex, acessory olfactory nucleus and olfactory tubercle.


Where does piriform cortex project

To the orbitofrontal cortex either directly or via the MD thalamus. The orbitofrontal cortex is an association area for olfactory and taste info, results in concious appreciation of smell.


Function of olfactory tubercle and amygdala in olfaction

Interconnected with hypothalamus and is involved in subconcious regulation of homestasis, cridcadian, repro and other biological patterns


Function of entorhinal cortex

feeds into hippocampus and plays role in storage and retreival of memories


Describe the difference in route of access of odorants to the olfactory epithelium during orthonasal and retronasal stimulation.

orthonasal: odors enter the nostril. Retronasal: odors from substances in the mouth curve backward past soft palate and enter the nasal cavity from the rear


List the output pathways and targets of the olfactory bulb. What behaviors or cognitive events are associated with each of the telencephalic olfactory target areas?



Contrast the neural pathways for taste and smell. What is the presumed neural correlate for the peculiar ability of odors to evoke emotional memories? How are odors represented in the olfactory bulb?



How can you tell the difference between taste, smell and trigeminal chemoreception in a clinical setting? How can you determine which modality is affected by a dysfunction or illness?