lec 20- Animal sensory systems part 2 Flashcards
how does chemoreception occur?
when chemicals bind to chemoreceptors and initiate action potentials in sensory neurons
what are the two senses recognized by chemoreceptors?
taste (gustation) and smell (olfaction)
what is the sensory transduction pathway used for chemoreception?
specialized sensory neurons
what are odorants and what do they do?
they are odour molecules that reach the nose and diffuse into a mucus layer in the roof of the nose and bind to membrane-bound receptor proteins, activating olfactory receptor neurons
where do the axons from the olfactory receptor neurons project to?
project up to the olfactory bulb, the part of the brain where olfactory signals are processed and interpreted
what are the 9 steps of signal transduction of an odorant receptor in the membrane of an olfactory receptor neuron?
- odorant molecule binds to the odorant receptor causing a conformational change in the odorant receptor protein
- this activates a G protein which activates adenylyl cyclase
- adenylyl cyclase converts ATP into cyclic AMP
- cAMP opens cAMP gated Na+/Ca2+ ion channels
- sodium and calcium influx causes depolarization of the neuron
- calcium influx also causes activation of Ca2+ gated Cl- channels
- Cl- leaves further depolarizing the neuron
- Na+, Ca2+ influx and Cl- efflux cause depolarization of the neuron which activates voltage gated Na+ channels
- action potentials are generated
in which way do action potentials travel in the olfactory receptor neurons?
towards the cell body, opposed to other neurons which go away from cell body
how many different odorant receptor proteins do humans have and how many are expressed in olfactory receptor neurons?
-100 but each olfactory receptor neuron only expresses one type of receptor protein
-each receptor can recognize more than one odorant
how do odorants have variable affinity?
because each odorant can bind to and stimulate more than one receptor
what is combinatorial coding of odorants?
an odorant can cause different magnitudes of responses in multiple receptors, these patterns of responses represent an odorants chemical identity
what is the glomeruli?
a distinct region in the olfactory bulb where olfactory receptor neurons that express the same single odorant receptor protein project to
how does the brain specify specific smells?
the brain interprets the intensity and pattern of activation of specific glomeruli to identify specific smells
what is the difference between photoreception and olfaction?
photoreception:
receptor proteins- 3
receptor cell- modified epithelial cell
receptor- g protein coupled
activation causes- hyperpolarization
secondary messenger- cGMP
olfaction:
receptor proteins- 100s
receptor cell- receptor neuron
receptor- G protein coupled
activation causes- depolarization
secondary messenger- cAMP
what are pheromones?
chemicals secreted into the environment and cause a physiological or behavioural change in members of the same species, pheromone receptors are localized in a distinct region from the olfactory bulb called vomeronasal organs (VNO)
