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BIO 435
Olfaction and Gustation
| Question | Answer | |
|---|---|---|
| What does sensory encoding represent? | stimulus features in neural signals | |
| What are the features of the stimulus? | -modality (type of stimulus) - location - intensity - duration | |
| What is the process of encoding stimuli? | sensory transduction | |
| What do sensory receptor cells do? | Sensory receptor cells change sensory stimuli into electrical signals | |
| What type of neuron is a receptor cell often known as? | bipolar neurons (some that have graded potentials) | |
| What type of receptors respond to chemical stimuli | chemoreceptors smell= receptors activated by volatile olfactants taste= receptors activated by tastants | |
| Where are olfactory receptor neurons located? | the olfactory epithelium | |
| What are olfactory receptor neurons (ORNs) | ORNs are the receptor neurons for olfaction where transduction occurs, they are bipolar neurons with cilia | the axons of the ORN are collectively known as the olfactory nerve |
| How often are ORNs regenerated? | ORNs live 4-8 weeks | |
| Which cells become the new ORNs when they are regenerated? | basal cells | |
| Why are ORNs constantly regenerated? | because our noses are constantly exposed to lots of toxins and chemicals in air and are not protected | |
| What do ORNs transduce? | odorants that are dissolved in the olfactory mucus | |
| What type of receptors do odorants bind to? | metabotropic; there are 1000 different types of receptors (in mice) | |
| How many types of receptors does each ORN have? | ONE; each odorant activates a unique combination of receptors | |
| How are receptors distributed in the olfactory epithelium? | Each receptor type is mostly confined to one of the four zones of the epithelium | |
| Describe the transduction mechanism for odorants | 1. odorant binds to the receptor 2. G(olf) (odorant metabotropic receptor) is activated and activates cyclase which produces cAMP 3. cAMP opens cation channels (releasing Ca2+ and Na+) | 4. Ca2+ opens up Cl- channels causing Cl- to leave the cell 5. Cl- leaving the cell results in more depolarization and the cell reaches action potential threshold |
| Where do action potentials in ORNs occur | In both the cell body and the axon | |
| Where do ORNs project? | ORNs project to the olfactory bulb (CNS) and glutamate is released onto second order neurons including mitral cells | |
| How does the olfactory system different between species? | Certain species have more ORNs than others (for example bloodhounds have 4 billions ORNS, rats have 15 million and humans have 12million) | |
| Where are receptor types segregated? | the olfactory bulb | |
| How many spots does every ORN that has a specific receptor converge onto in the olfactory bulb (glomerulus) | one or two spots | |
| Approximately how many ORN synapses are there on one glomerulus? | approx. 25,000 ORN synapses on 100 mitral cells | |
| How are odorants recognized? | population coding/each odorant activates a specific collection of receptors and to differing degrees | |
| Where do second-order neurons project? | the temporal lobe structures (directly) and the thalamus (indirectly) | |
| What do olfactory maps allow us to see? | The different types of receptors that are activated by different smells (a-pinene = piney/resinous scents; octanal = fruity, citrus) | |
| What is the equilibrium potential of olfactory cells? | -10mV | |
| Describe the pathway of odorant stimuli | 1. olfactory epithelium 2. mitral cells 3. olfactory cortex (olfactory tubercle and the piriform cortex) 4. thalamus | |
| What connections allow for strong emotional memories to be tied to specific odors? | The amygdala | |
| What connections allow us to perceive smell? | orbitofrontal cortex | |
| What reduces our perception of odors over time? | olfactory adaptation | |
| Why does olfactory adaption occur? | Phosphorylation of receptors can desensitize it; phosphodiesterase also breaks down cAMP and neurons are no longer able to become depoloarized | |
| What can the thalamus do during olfactory adaptation? | Redirect the odor | |
| How many taste buds does each papillae contain? | Each papillae can contain 1 to hundreds of taste buds | |
| How many taste receptor cells does each taste bud contain? | 50-150 | |
| What type of cells are taste receptor cells? | modified bipolar neurons (however they may be capable of producing action potentials) | |
| What extends out of taste receptor cells in the taste pore? | Microvilli that are full of taste receptors | |
| At what concentrations do receptor cells have high specificity? | low concentrations | |
| At what concentrations can taste receptor cells respond to multiple tastants? | higher concentrations | |
| What is broad tuning of taste cells used for? | Broad tuning can tell you which tastes the cell will respond to | |
| Are there specific parts of the tongue that respond to specific types of tastes? | NO, all parts of the tongue respond to all types of tastants | |
| During the transduction of salty tastants, what types of channels are always open? | Amiloride-sensitive Na+ channels | |
| When are amiloride-sensitive Na+ channels closed? | When amiloride is present | |
| What happens when salty tastants enter the cell? | Na+ enters the channel causing the cell to depolarize, voltage gated Ca2+ channels open and serotonin is released | |
| What type of receptors can very salty things activate? | Bitter and sour receptors | |
| Describe the transduction of sour tastants | 1. H+ enters through the proton channel when sour tastant enters the mouth 2. H+ closes the K+ channel 3. depolarization occurs and voltage-gated Ca2+ channels are opened and serotonin is released | |
| Describe the transduction of bitter, sweet, and umami tastants | * Each tastant activates separate metabotropic receptor * 1. Gq protein activates phospholipase C, which converts PIP2 and IP3 2. IP3 releases Ca2+ from intracellular stores 3. ATP releases | |
| What transmits information from taste receptor cells to the brainstem | Cranial nerves | |
| Describe cranial nerve VII (CN VII) | sensory neurons from the anterior2/3 of tongue | FACIAL NERVE |
| Describe cranial nerve IX (CN IX) | sensory neurons from the posterior 1/3 of tongue | GLOSOPHARYGEAL NERVE |
| Describe cranial nerve X (CN X) | sensory neurons from throat | VAGUS NERVE |
| Describe the taste pathway to the cortex | 1. Synapse 1= gustatory nucleus (NTS) in medulla 2. Synapse 2= ventral posterior medial thalamus 3. Synapse 3= primary gustatory cortex in insula | |
| What are other medulla areas responsible for? | reflex control, swallowing, gagging, vomiting, and salivation | |
| What are the hypothalamus and amygdala responsible for? | hunger and emotion | |
| Where does the orbitofrontal cortex receive input from? | olfactory pathways, gustatory cortex, and somatosensory pathways (feel of the food in your mouth) | |
| What does the combination of information in the orbitofrontal cortex allow for? | The complete taste perception | |
| What allows for recognition of taste | population coding; information about different tastants converge along the gustatory pathway and the optimal response stimulus will begin to merge taste types | |
| How does the brain determine the taste | The brain looks at overall activity of all cells to determine the taste |
Created by:
keiannaowens
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