Chemical senses - Olfactory

Question 1

what does the term olfactory refer to

Answer 1

refers to the sense of smell

Question 2

what are advantages of olfaction

Answer 2

locate and track food prey at a distance
long distance warning beyond line-of sight and in the dark
sexual attraction
hedonic reward system - Gastronomic delights; fine wine; etc

Question 3

what does hedonic reward system

Answer 3

refers to the neural circuitry in the brain that is associated with experiencing pleasure and rewards

Question 4

what are some physiological and behavioural responses to odours

Answer 4

visceral responses: -smell food–> salivation and gastric motility
- noxious smell –> gag
infants recognize mothers by scent
mothers can recognize the scent of her baby
women housed together synchronize menstrual cycles (McClintook Effect)

Question 5

what do the food molecules hit in the nose

Answer 5

they reach the neuroepithelium (the olfactory epithelium)

Question 6

what does the olfactory epithelium contain

Answer 6

olfactory sensory neurons (ONS) surrounded by columnar supporting cells
basal cells

Question 7

explain the olfactory sensory neurons

Answer 7

Apical dendrite of sensory neuron projects through support cells to nasal cavity, and is capped by dendritic cilia projecting into specialized mucus in the cavity. The cilia have receptor sites for odorant molecules and are thus structures for olfactory signal transduction Olfactory sensory neurons (OSN) are fairly short-lived (1-2 months), and regenerate from basal stem cells Cribriform plate: bony structure with tiny holes, separating the nose from the brain. OSN axons pass through these holes to enter the brain

Question 8

what are mammalian odour receptors related to

Answer 8

other chemosensory receptors

Question 9

what are T1R and T2R

Answer 9

taste receptors

Question 10

what is V3R

Answer 10

vomeronsal receptors

Question 11

how are odors detected

Answer 11

by receptors and transduced into an electrical signal resulting in the generation of an action potential

Question 12

how does the action potential travel

Answer 12

down the axon of the olfactory receptor cell eventually meets the other axons and forms the olfactory nerve (CN I)

Question 13

what type of receptors are olfactory receptors

Answer 13

G protein-coupled receptors (GPCI) which activate adenyl cyclase type-III via the C protein, Golf

Question 14

What is cAMP

Answer 14

A signalling molecule (second messenger)

Question 15

What does cAMP do

Answer 15

Opens a nonselective, cyclic-nucleotide-gated (CNG) cation channel

Question 16

What does the opening of the CNG cation channel do

Answer 16

Depolarises the ciliary membrane by allowing the influx of Na+ and Ca2+ and Cl- leaves down it’s concentration gradient which further depolarises the cell

Question 17

what do neuronal Cl- channels normally mediate

Answer 17

inhibitory responses (think GABAa receptor)

Question 18

do OSNs have a high intracellular Cl- concentration or not

Answer 18

yes they do because of the membrane pup NKCC1