Flavor and Gustation (quiz 2)

What is flavor?

chemical senses of gustation and olfaction + oral sensory input + saliva

diverse interaction of several sensory systems

What are the two major systems for distinguishing flavors?

taste and smell

What type of input contributes to information about flavor quality?

somatosensory input

What helps maintain acuity of taste receptor cells?

saliva

What are the functions of saliva as far as maintaining acuity?

solvent for polar solutes, transports solutes to taste receptors, buffer for acidic foods, helps repair lingual epithelium

Which cranial nerves are involved in taste?

Facial VII, Glossopharyngeal IX, and Vagus X

What are the types of taste buds?

fungiform papillae, circumvallate papillae

Which cranial nerve innervates Fungiform Papillae?

facial nerve VII

Which cranial nerve innervates circumvallate papillae?

glossopharyngeal nerve IX

What are the non-taste bud relates structures involved in taste?

epiglottis and esophagus

which cranial nerve innervates the epiglottis and esophagus?

vagus nerve X

Where does sensory transduction of taste start?

on microvilli of taste cells

What is the lifetime of a taste cell?

approx 2 weeks

How do taste cells regenerate?

from basal cells

What processes effect how a person experiences taste?

taste reception and transduction

What are the five flavor types?

sweet, salty, bitter, sour, umami

What do taste buds respond to?

taste buds have different taste receptors that respond to different taste types

Which type of channel detects salt taste? (NaCl)

Na+ channels

What type of channels detect sour or acidic solutes? (H+)

Na+ channels, H+ transport directly into cell, some block K+ efflux

What type of channels detect sweet/sugar compounds?

G-protein coupled 2nd messenger pathway, reduced K+ efflux and Ca2+ accumulation depols membrane

How are bitter compounds detected?

block K+ efflux, depols membrane, G-protein coupled cAMP protein kinase pathway blocking K+ channels, G-protein signaling pathway that activates phospholipase C and releases Ca2+

How is umami detected?

ligand-gated ionotropic glutamate receptors, coupled to Ca2+ and G-proteins

What is the main gustatory pathway in humans?

oral cavity > nucleus tractus solitarius > VPM > gustatory cortex

What is the VPM?

ventral posterior medial nucleus of the thalamus

Where is the gustatory cortex located?

In the insular cortex

What type of projections does the gustatory pathway use?

ipsilateral

What gustatory pathway structure is unique to non-human mammals?

Parabrachial nucleus, which relays info to the amygdala and lateral hypothalamus

What is the gustatory pathway in non-human mammals?

cranial nerves VII, IX, X > parabrachial nucleus > amygdala and lateral hypothalamus

What are the two types of gustatory coding?

spatial and ensemble, which are activation patterns encoded by a subset of neurons that represent the sensory stimulus

What are the other common taste perceptions?

astringency, pungency, fat, starch, metallic

What roles does the trigeminal nerve V play in flavor

relays somatosensory info, contains lingual nerve branch, nociception and TRP receptors

What are the specific somatosensory functions of the trigeminal nerve V that play a role in gustation?

mechanical forces, thermal input, chemical nociception, burning sensation, TRPV1 and TRPA1

What receptors encode information about bitter biomolecules?

TRPM4 and TRPM5

What receptors encode information about temperature and thermal sensation?

TRPM 8

What mechanisms can drosophila use to get nutrients during starvation? (proboscis extension reflex)

sweet receptor neurons are turned on, while bitter receptor neurons are turned off

How are bitter receptor neurons turned off in PER?

OA-VLs release octopamine and tyramine neurotransmitters that control the activity of bitter sensory neurons

What is olfaction?

chemosensory system for discriminating among chemicals

How many different odors can humans distinguish?

between 1K and 4K, possibly up to 6K

What are the 6 odor classifications?

floral, fruit, spicy, resin, burnt, putrid

What is the nature of odorant compounds?

they are volatile (easily evaporate)

What cranial nerve transmits olfactory information

olfactory nerve CN I

How do we interpret odors?

inhalation and transport of volatile molecules to receptors through olfactory mucosa

What is the receptor surface for olfactory transduction?

the olfactory epithelium (mucosa) inside the nasal cavity

What type of cells are located in the olfactory epithelium?

olfactory receptor cells (ORC), supporting cells, columnar cells that secrete mucus, basal cells (source of new ORC)

How long does it take for basal cells to become ORC?

5-8 weeks

What are the components of the mucus produced by columnar cells?

water, polysaccharides, salts, enzymes, odorant binding proteins, antibodies

What determines acuity of smell?

size of epithelium and density of ORCs

What are ORCs composed of?

a single dendrite with 5-25 cilia embedded in the mucosa

What are the function of the cilia on ORCs?

each cilia can express up to 40 specific receptor proteins, cilia receptor proteins bind dissolved odorants

What is the order of olfactory transduction pathway?

ORCs > receptor proteins coupled to Golf proteins > activation of Golf proteins initiates signaling pathway > cation channels open > membrane depolarization to olfactory bulb > CNS via olfactory bulb

What makes up the olfactory bulb?

glomeruli

What are glomeruli?

modules of the olfactory bulb where ORCs synapse. Each glomerulus receives input from only one type of ORC

The action potential frequency of olfaction is proportional to what?

the concentration of the odorant molecules

How can olfactory APs be reduced?

adaption or desensitization of the receptor or reduction in the production of cAMP

How can glomeruli control action potential frequency?

lateral inhibition can occur across them by interneurons

What are interneurons?

inhibitory periglomerular cells that synapse onto their adjacent glomeruli

What is spatial coding for olfactory?

a physical pattern of activation of specific neurons associated with odorants

What is population coding for olfaction?

complex odors contain multiple chemicals, which activate multiple types of ORCS and glomeruli. The combination of total responses produce information, with different neurons having different response rates