Term
| How are the receptors of smell and taste stimulated? |
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Definition
| By binding of chemical stimulants--oderants, which are airborne, and tastants which are conveyed to receptors via fluid. |
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Term
| T/F The senses of smell and taste use the same receptors, peripheral pathways, and differing CNS circuitry. |
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Definition
| False. Smell and taste have different receptors, peripheral pathways, and differing CNS circuitry. |
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Term
| What is the site of olfactory transduction? |
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Definition
| The cilia of the olfactory receptor neurons. |
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Term
| Give an overview of the olfactory transduction cascade. |
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Definition
1.The odorant binds to the olfactory binding protein.
2.The olfactory G protein, Golf, is activated
3.Cyclic nucleotide gated ion channels open
4. Calcium activated chloride channels amplify the signal |
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Term
| T/F Olfactory receptor proteins belong to the same super family as metabotropic neurotransmitter receptors. |
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Definition
| True. Olfactory receptor proteins are G-protein linked and have a molecular structure which passes through the plasma membrane a total of seven times. |
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Term
| What does Golf stimulate? |
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Definition
| Golf stimulated adenylyl cyclase, leading to increased cytoplasmic cAMP concentration. |
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Term
| What does cAMP trigger inthe olfactory and taste sensory systems? |
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Definition
| cAMP binds to and opens a nucleotide gated ion channel (CNG channels) that are permeable to both Na and Ca. In the olfactory system cAMP binds to and opens CNG channels. In bitter taste transduction cAMP along with cGMP inhibit the opening of a CNG channel, so stimulation of PDE decreases cAMP/cGMP concentration and allows the opening of CNG channels. |
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Term
| How is the signal amplified? |
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Definition
| Amplification occurs by calcium activated chloride channels. Calcium influx through one of the CNG channels stimulates a chloride permeable ion channel. The inward depolarizing current created by chloride efflux further depolarizes the receptor neuron membrane. |
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Term
| Why is the chloride current excitatory? |
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Definition
| Chloride concentration in the olfactory system is different than other parts of the body. Chloride concentration in the neuron is much higher than chloride concentration in the extracellular fluid, so that when chloride channels are open chloride exits the neuron and the pushing the cell closer to positive. |
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Term
| What are factors that lead to adaptation of the olfactory system? |
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Definition
-Odorant diffusion and transport away from receptors
-Breakdown of odorant molecules by enzymes in mucous
-Calcium binding to calmodulin and the resulting complex binding and inhibiting the CNG channels, which are required for transduction |
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Term
| T/F Odorant receptor neurons express multiple receptor protein genes. |
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Definition
| False. Odorant receptor neurons express only one odorant receptor genes that is coded by one gene. |
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Term
| How can humans detect 20,000 different smells if they only have about 1,000 different receptor proteins? |
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Definition
-Population coding- the pattern of firing of all the different neurons codes for various smells allowing for many recognizable combinations
-temporal coding-olfactory bulb and cortex generate oscillating patterns of activity that vary systematically with the nature of the chemical odorant. |
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Term
| How is odorant concentration encoded? |
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Definition
| Odorant concentration is coded by firing rate. higher odorant concentrations result in more rapid action potential generation. |
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Term
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Definition
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Term
| Where does central processing for our sense of smell take place? |
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Definition
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Term
| T/F All receptor neurons innervating one glomerulus contain the same olfactory receptor protein. |
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Definition
| True. Unlike the scattered distribution of receptor types across the ofactory epithelium each glomerulus in the olfactory bulb receives axons only from receptor neurons expressing the same olfacotry receptor gene. |
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Term
| What might be a purpose of the convergence of the olfactory receptor axons into glomeruli in the olfactory bulb? |
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Definition
| Could provide an increase in sensitivity to the olfactory system. |
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Term
| What synaptic connections run to the glomeruli? (This might not be phrased correctly) |
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Definition
| Olfactory glomeruli contain excitatory and inhibitory internuerons. Glomeruli are connected to each other Glomeruli receive descending input from the brain |
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Term
| What is a possible function for the organization of the olfactory bulb? |
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Definition
| To organize chemosensory input into broad categories. |
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Term
| Where does output from olfactory bulbs go? |
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Definition
| Passes through olfactory tracts directly to olfactory areas of the cerebral cortex. |
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Term
| What are the tastes humans can recognize? |
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Definition
-Sweet
-Sour
-Bitter
-salt
-Umami |
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Term
| Where are taste receptor cells? |
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Definition
| Taste receptor cells are within taste buds which cluster into papillae. |
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Term
| What effect do tastants have on taste receptor cells? |
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Definition
| Tastants cause taste receptor cells to hyperolarize or depoarize. If a receptor potential is sufficiently depolarizing then voltage gated calcium channels are opened, calcium enters and neurotransmitter is released, exciting the post-synaptic sensory axon, triggering action potentials. |
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Term
| T/F Most taste receptor cells respond to only one basic taste. |
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Definition
| False. Most taste receptor cells respond to two or more basic tastes. The nature and strength of the response depends on the specific transduction mechanism present in the cell. |
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Term
| What are the various mechanisms for taste transduction? |
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Definition
Tastants may:
1) Pass through an ion channel (salt, sour)
2) Bind to and block ion channels (sour, bitter)
3) Bind to and open ion channels (some amino acids)
4) Bind to membrane receptors that activate second messenger systems which in turn open or close ion channels (sweet, bitter, umami) |
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Term
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Definition
| Taste buds that detect salt have epithelial sodium channels (ENaC). Eating salty foods increases the concentration of salt outside the apical microvilli increasing the Na driving force and causing sodium influx into the receptor cell. The inward sodium current depolarizes the receptor cell, activating voltage gated calcium channels and triggering transmitter release. |
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Term
| How are voltage gates sodium channels of axons different from epithelial sodium channels for taste transduction? |
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Definition
| Epithelial sodium channels (ENaC) are not voltage gates, instead they are always open. |
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Term
| What compounds can affect the epithelial sodium channels? |
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Definition
-Amiloride- blocks epithelial sodium channels
-anions can inhibit the salt response-the mechanism is unknown, however larger anions causes a greater inhibition. |
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Term
| What is the pH of foods that taste sour? |
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Definition
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Term
| What are the mechanisms for sour taste transduction? |
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Definition
-Protons can permeate the amiloride sensitive sodium channels (ENaC)creating an inward current
-Protons can also block potassium channels, reducing the resting outward current.
These actions depolarize the taste receptor cell causing voltage gated calcium channels to open, calcium to enter the cell, and neurotransmitters to be released onto the afferent axons |
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Term
| Describe the mechanisms of sweet taste transduction that involve protein kinase A. |
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Definition
| -A tastant binds to the sweet receptors which stimulates a g protein. The g protein stimulates adenylyl cyclase causing the formation of cAMP. cAMP activates PKA which phosphorylates a calcium channel causing it to close. This causes the cell to depolarize. (The depolarization opens voltage gated calcium channels allowing calcium to flood in and signal NT release) |
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Term
| Other than phosphorylating a potassium channels, what other mechanisms can allow for NT release from sweet taste receptors? |
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Definition
| - A different G protein can signal for phospholipase C (PLC) release which in turn causes the formation of inositol triphosphate (IP3) IP3 releases calcium from organelles. The increase in calcium causes NT release. -Another type of sweet receptor is thought to be directly linked to cation channels, though little is known of the mechanism |
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Term
| What is an advantage to being able to detect bitter tastes? |
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Definition
| It allows for detection of many poisons. |
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Term
| Describe the mechanism for detecting bitter tastes that does not involve g proteins. |
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Definition
| Quinine or other bitter tastants will directly block potassium channels causing the receptor to depolarize, calcium channels to open, and NT released. |
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Term
| Describe the two mechanisms for detecting the bitter taste that use g proteins. |
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Definition
-In one mechanism bitter tastants cause g proteins to stimulate PLC which in turn stimulates the formation of IP3 which leads to the release of calcium from organelles causing NT to be released
-the other g protein mechanisms involves g proteins stimulating PDE which degrades cAMP and cGMP. The decrease in cAMP and cGMP stops the inhibition of cyclic nucleotide gated ion channels (CNG)allowing an increase of cations (Na, Ca) into the receptor causing depolarization, influx of Ca, and release of NT. |
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Term
| Describe the two mechanisms for detecting the taste of amino acids. |
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Definition
-Some amino acid tastant receptors are directly linked to cation channels so that binding of a tastant keeps the channels open allow an influx of Na and Ca. This depolarizes the cell allowing voltage gated calcium channels to open, leading to an influx of Ca, which signals the release of NT.
-a second mechanisms involves an umami receptor that is g protein linked. Binding of a tastant stimulates the release of g protein which blocks adenylyl cyclase which leads to a decrease in cAMP in the cell. This modifies an unidentifiable channel (could be a CNG) leading to the depolarization of the receptor cell. |
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Term
| T/F Individual taste receptor cells respond to more than one taste. |
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Definition
| True. Consequently, taste afferent fibers also respond to more than one taste, although they may respond best to one preferred taste. |
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Term
| T/F. Taste is based upon the labeled line mechanism in which there is one receptor type and one pathway for each stimulant. |
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Definition
| False. Probably involves some degree of population coding |
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