Flashcards in chemosensation Deck (28)
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?