Moyes and Schulte .docx - Moyes and Schulte Chapter 7...

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Moyes and Schulte Chapter 7: Sensory Systems Chemoreception Odorant receptors are G protein coupled Odorant molecule binds to an odorant receptor, the receptor undergoes a conformational change that sends a signal to an associated G protein, G-olf Activated G-olf signals via adenylate cyclase, activating a signal transduction pathway which causes depolarization which creates action potential An alternative chemosensory system detects pheromones G protein coupled receptors of the vomeronasal organ activates a phospholipase C based signal transduction system which causes an ion channel in the transient receptor potential (TRP) to open, membrane potential, then electrical signal Invertebrate olfactory mechanisms differ from those in vertebrates Olfactory sensilla have a small pore at the tip to allow odorants to cross the exoskeleton Drosophila - each olfactory neuron expresses a single odorant receptor and olfactory neurons likely code odorant information combinatorially C. Elegans , each olfactory neuron expresses several different odorant receptors and thus the odorant code cannot be a simple combinatorial system like that found in mammals Taste buds are vertebrate gustatory receptors Dissolved chemicals from food, tastants, enter through a pore and contact the taste receptor cell Vertebrate taste receptors use diverse signal transduction mechanisms Sodium and hydrogen compete for the access to the channel, channels are probably important for the perception of sourness for animals with relatively low sodium levels in saliva Umami caused by L-glutamate is detected by multiple types of G protein coupled receptors Glutamate binds to glutamate receptor, conformational change, activates g protein, activates a phosphodiesterase that degrade cAMP into AMP, decrease in cAMP triggers neurotransmitter release Signal transduction pathways in taste receptor cells Salty: 1. Sodium enters through sodium channel 2. Depolarization opens voltage gated calcium channel 3. Influx of calcium causes neurotransmitter release Sour:
Moyes and Schulte 1. Hydrogen ions block potassium channel 2. Prevents potassium from leaving the cell 3. Depolarization opens calcium channels 4. Influx of calcium causes neurotransmitter release Sweet: 1. Sweet substance binds to receptor causing conformational change 2. Activated G protein, gustducin, activates adenylate cyclase 3. AC catalyzes conversion of ATP to cAMP 4. cAMP activates protein kinase that phosphorylates and closes potassium channel 5. Depolarization opens calcium channel 6. Influx of calcium causes neurotransmitter release Bitter: 1. Bitter substance binds to receptor causing conformational change 2. Activated G protein, transducin, activates phospholipase C 3. PLC catalyzes conversion of PIP2 into the second messenger IP3 4. IP3 causes release of calcium 5. Influx of calcium causes neurotransmitter release Mechanoreception Touch and pressure receptors Baroreceptors detect pressure Tactile

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