Chemosensory Flashcards
What two senses does chemosensory cover in vertebrates?
Gustation and olfactory
What is the main differences between gustation and olfactory?
Gustation needs direct contact, olfactory can be sensed over distance (airborne molecules).
Describe the human olfactory system.
The olfactory epithelium is found in the upper part of the nasal cavity. The olfactory epithelium is lined with the dendrites of sensory neurons containing olfactory receptors. The sensory neurons terminates in glomeruli in the olfactory bulb located right above the nasal cavity. Here the signal is passed from the sensory neurons to mitral cells, and transmitted to the brain.
Describe the general signal transduction in vertebrate olfactory signaling.
Odorant binds to GPCR –> G-alfa-olf dissociates from G-beta-gamma and activates ADCY3 –> increase of [cAMP] –> cAMP gates CNGA2 –> influx of Ca^2+ and Na^+ –> depolarization –> AP
Describe the termination of the olfactory signal in vertebrates.
The increase of [Ca^2+] after the signal transduction results in the activation of SLC24A4 (a Ca^2+/Na^+/K^+ transporter) transporting Ca^2+ out of the cell. Furtermore the increase of [Ca^2+] results in the formation of CAMKII-CaM-Ca^2+ complex which phosphorylates and inhibits ADCY3, and the formation of PDE1C-CaM-Ca^2+ which coverts cAMP to AMP. The increase of [cAMP] results in the formation of PKA-cAMP which together with GRK phosphorylates the GPCR. Lastly, RGS2 ensures the reassociation of the G-alfa with the GPCR.
Describe the CO_2 sensing mechanism in mouse.
CO_2 is taken up by the cells in the vomeronasal organ –> carbonic anhydrase II (CAII) converts CO_2 to HCO_3^- + H^+ –> HCO_3^- activates GC-D (guanylyl-cyclase) –> GC-D converts GMP to cGMP –> cGMP gates a CNG channel –> influx of Ca^2+ and Na^+ –> depolarization –> AP
What is the vomeronasal organ?
An organ in certain vertebrates (rodents, horses), amphibians, snakes and lizards expressing vomeronasal receptors, used to detect pheromones for social and reproductive behaviour, and sometimes CO_2.
Describe the Flehman response.
Closing the nostrils with the upperlip, opening the mouth (where the opening to the vomeronasal organ is located) and lifting the head. A behaviour found in animals with a vomeronasal organ, used to detect pheromones.
Describe the pheormone sensing in verterbrates.
Pheromone binds to GPCR –> G-beta-gamma activates PLC-beta-2 –> –> DAG gates TRPC2 –> influx of Ca^2+ and Na^+ –> depolarization –> AP
What are the main differences between olfaction in vertebrates and invertebrates?
Invertebrate olaftion: Ionotropic signalig, inverted structure of the receptors, dimeric receptors (one binds the ligand, the other is important for complex formation and transport to the membrane)
Where are the olfatory organs located on invertebrates?
Mainly on antannas or on sensory cillia.
Describe the olfactory system in flies.
OSNs located in the peripheral organs (antenna/sensory cillia) terminates in glomeruli in the antennal lobe, signaling to PNs. PNs signal through the mushroom body and terminates in the lateral horn signaling to LHON.
Describe the organisation of the vertebrate taste bud. What structures and cells are
present, what are their functions?
Gustatory cells (chemoreceptive cells with microvilli), basal cells (replacing the gustatory cells) and supporting cells (secreting cells, creates the microenvironment)
How are the chemoreceptors of arthropods organized? Where do they typically have
their “nose”?
Organized in setea, a hollow “hair” with cillia in the lumen with pores where the odorants can enter. The nose are typically the antenna, otherwise not known.
What ways are the odours filtered during acquisition?
The odours are filtered through pores (in the cutical of athropods), by odour binding proteins and by receptors. Sniffing and antenna flickering are an active way of filtering.
