olfaction and gustation

Question 1

what are the 4 reasons why we need a sense of smell

Answer 1

detec harmful substances, hedonistic value/pleasure for appetite, affective/emotional component (connected to limbic system), mode of communication (pheromones)

Question 2

smells can be evoked by…

Answer 2

specific airborne chemicals or numerous compounds

Question 3

what does olfactory mucosa contain

Answer 3

specialised neuroepithelium for olfaction which projects to the main olfactory bulb MOB

Question 4

what does olfacory mucosa line and compare humans to dogs

Answer 4

nasal septum and upper turbinates in nasal cavity
humans 10cmsqrd
dogs 170cmsqrd

Question 5

what does neuroepithelium do

Answer 5

samples volatile substances from external air and oropharynx which is important for flavour perception

Question 6

what produces mucous and what does that do

Answer 6

bowmands glands produce mucous which prevents cilia from dying out

Question 7

where are odorant receptors located

Answer 7

on the olfactory sensory neuonrs’ cilia membrane

Question 8

waht does the sensory neurons project through

Answer 8

through bone into the olfactory bulb

Question 9

what do basal cells do

Answer 9

stem cells for replacement of olfactory sensory neurons every 10-30 days

Question 10

describe the gpcr cascade when odorant molecules bind to receptor

Answer 10

gtp stimulates adenylate cyclase type III, increased cAMP -> open cyclic nucleotides gated cation channels for depol and AP

Question 11

what does amplification by G proteins allow

Answer 11

allows extremely low detection thresholds

Question 12

each olfactory receptor neurons expresses…

and where do you find these receptors

Answer 12

a single membrane receptor protein

and each receptor expressing the same protein is randomly dispersed throughout zones within the olfactory epithelium

Question 13

a broad range of odorants is detected by…

Answer 13

a single olfactory receptor, which means they are broadly tunes

Question 14

how do you get odour discrimination?

Answer 14

derived from the population code of neural activity, in terms of which receptors detect the odour across the population of receptors

Question 15

what does the same receptor class in the epithelium do?

Answer 15

project to the same golmerulus

Question 16

what produces a spatial map in the olfactory pathway?

Answer 16

each glomerulus receives input from one class of receptor neurons which are grouped together in zones

Question 17

what can interactions between glomeruli reflect?

Answer 17

specific patterns of odour

Question 18

what are the 3 elements of olfactory processing within glomeruli

Answer 18

local interneurons
inter-glomerular connections
projection neurons to cortex

Question 19

how is localised neural activity in olfactory bulb revealed and what does it show

Answer 19

through voltage and ca2+ sensitive dyes

show stimulus specific activity of many neurons

Question 20

what does recent evidence show about neuronal encoding in glomeruli

Answer 20

use timing properties

Question 21

describe anosmia, hyposmia and parosmia

Answer 21

anosmia = specific inability to smell something well (eg genetics/covid)
hyposmia = general impaired olfactory ability 
parosmia = abnormal odour perception

Question 22

where do projections from olfactory bulb go

Answer 22

• to contralateral olfactory bulb
• limbic system - links to emotion
• learning areas
• frontal cortex for integration and perception of smell and taste

Question 23

why do we need to taste

Answer 23

pleasure, test edibility, GIT reflex, homeostasis

Question 24

what are taste cells and what do they comprise

Answer 24

they are modified epithelial cells and there are 150 per taste bud which synapses with taste afferent nerve

Question 25

most taste receptor cells respond to ….

Answer 25

more than one stimulus type

Question 26

single afferent nerves innervate ….

Answer 26

multiple taste receptors

Question 27

what happens in terms of graded receptor potentials for the different flavours

Answer 27

salt and sour = dpol, VGa2+ channnels open -> ntsm release

seet, bitter umami = second messegners increase CA2+ -> stim ntsm release => amplifications of weak signals

Question 28

describe taste pathway

Answer 28

primary taste afferents synapse in nucleus of solitary tract in medulla (integrates in case of reflex)
project into thalamus and primary cortex

Question 29

where and how is flavour perceived

Answer 29

obitofrontal cortex smell + taste modailites are integrated