olfaction and gustation Flashcards
what are the 4 reasons why we need a sense of smell
detec harmful substances, hedonistic value/pleasure for appetite, affective/emotional component (connected to limbic system), mode of communication (pheromones)
smells can be evoked by…
specific airborne chemicals or numerous compounds
what does olfactory mucosa contain
specialised neuroepithelium for olfaction which projects to the main olfactory bulb MOB
what does olfacory mucosa line and compare humans to dogs
nasal septum and upper turbinates in nasal cavity
humans 10cmsqrd
dogs 170cmsqrd
what does neuroepithelium do
samples volatile substances from external air and oropharynx which is important for flavour perception
what produces mucous and what does that do
bowmands glands produce mucous which prevents cilia from dying out
where are odorant receptors located
on the olfactory sensory neuonrs’ cilia membrane
waht does the sensory neurons project through
through bone into the olfactory bulb
what do basal cells do
stem cells for replacement of olfactory sensory neurons every 10-30 days
describe the gpcr cascade when odorant molecules bind to receptor
gtp stimulates adenylate cyclase type III, increased cAMP -> open cyclic nucleotides gated cation channels for depol and AP
what does amplification by G proteins allow
allows extremely low detection thresholds
each olfactory receptor neurons expresses…
and where do you find these receptors
a single membrane receptor protein
and each receptor expressing the same protein is randomly dispersed throughout zones within the olfactory epithelium
a broad range of odorants is detected by…
a single olfactory receptor, which means they are broadly tunes
how do you get odour discrimination?
derived from the population code of neural activity, in terms of which receptors detect the odour across the population of receptors
what does the same receptor class in the epithelium do?
project to the same golmerulus
what produces a spatial map in the olfactory pathway?
each glomerulus receives input from one class of receptor neurons which are grouped together in zones
what can interactions between glomeruli reflect?
specific patterns of odour
what are the 3 elements of olfactory processing within glomeruli
local interneurons
inter-glomerular connections
projection neurons to cortex
how is localised neural activity in olfactory bulb revealed and what does it show
through voltage and ca2+ sensitive dyes
show stimulus specific activity of many neurons
what does recent evidence show about neuronal encoding in glomeruli
use timing properties
describe anosmia, hyposmia and parosmia
anosmia = specific inability to smell something well (eg genetics/covid) hyposmia = general impaired olfactory ability parosmia = abnormal odour perception
where do projections from olfactory bulb go
- to contralateral olfactory bulb
- limbic system - links to emotion
- learning areas
- frontal cortex for integration and perception of smell and taste
why do we need to taste
pleasure, test edibility, GIT reflex, homeostasis
what are taste cells and what do they comprise
they are modified epithelial cells and there are 150 per taste bud which synapses with taste afferent nerve
most taste receptor cells respond to ….
more than one stimulus type
single afferent nerves innervate ….
multiple taste receptors
what happens in terms of graded receptor potentials for the different flavours
salt and sour = dpol, VGa2+ channnels open -> ntsm release
seet, bitter umami = second messegners increase CA2+ -> stim ntsm release => amplifications of weak signals
describe taste pathway
primary taste afferents synapse in nucleus of solitary tract in medulla (integrates in case of reflex)
project into thalamus and primary cortex
where and how is flavour perceived
obitofrontal cortex smell + taste modailites are integrated
