taste and olfaction Flashcards
flavour includes
taste
smell
other nerve endings in the mouth
sense of taste
gustation
MSG
monosodium glutamate- savoury
parts on a toungue
epiglottis
cranial nerve x
cicrumvallate papillae: big dots on back
cranial nerve ix
folate papilla: middle of tongue
cranial nerve VII
fungiform papillae: small dots in front
what are the things being sensed on the tongue
sucrose
NaCl
HCL
Quinine
water
what are the individual receptors on the tongue
chemoreceptors life span of 10 days and are renewable
what must taste molecules do in the tongue
dissolve in saliva
Na influx
salt tastant transduced
H blocks K channel
sour tastant transduced
glucose or similar chemical activates g protein CAMP- phosphorylation and blockage of K
sweet tastant transduced
more diverse tastants- alkaloids- g protein gusductin- inhibit phosphodiesterase- increase CAMP
bitter tastant transduced
triggered by amino acid especially glutamate- g protein IP3- Ca release from internal store- activation of monovalent selective cation channel
umami
nerve contributions in the tongue
VII: ant in 2/3 of the tongue, there may also be taste buds on the palate (roof of mouth)
IX: posterior 1/3 of tongue
X: mino contribution especially poteriorly around epiglottis
taste pathway in the CNS
at the tongue
in the medulla oblongata (solitary nucleus also connects to the area postrema)
in the pons
to the ventro-posterior medial thalamus, hypothalamus and amygdala
to the insular and orbital cortex
across fibre hypothesis
proposes that the pattern of responses to a particular stimulus across all fibres is the central feature of coding
individual TRCS are tuned to multiple taste quallities. same afferent fibres carries info for more than one modality
or TRC are still tuned to single taste qualities but the same afferent fibre carries info for more than one taste modality
response of individual fibres to different tastants
patterns of responses of cells in a population help discriminate tastes
labelled line model of taste
the receptor cells are tuned to respond to a single tastemodalities and are innervated by individually tuned nerve cells. each taste quality is specified by the activity of non overlapping cells and fibres
how is taste discriminated
connectivity (topography) and also activity patterns within the population
olfaction
sense of smell
how many olfactory receptor cells are there
5 mill
how many dog olfactory receptor cells are there
4 billion
surface area of olfactory epithelium in humans
10 cm^2
area of olfactory epithelium in some dogs
170 cm^2
smell for diagnosis
infection after surgery from bacteria may smell line wine cellar (musty)
breath of diabetic in coma smells like apples
garlic smell can indicate arsenic poisoning
olfactory epethilium location
lies high wihtin the nasal cavity and its olfactory cells project to the olfactory bulb
what do olfactory cells synapse with
secondary sensory neurons in olfactory bulb
how long do olfactory cells in olfactory epethilium live for
2 months replaced by new cells that must find their way to olfactory bulb 30-60 days
where is odor first detected
in the cilla of olfactory receptor neuron. strong enough signal generates action potential in neuron
olfactory receptor neuron
ORN
signal transduction of odorant
odorant
golf
inc in CAMP
open cyclic nucleotide gated channels (CNG channels)
what controls odor adaptation and excitation
Ca signal
Ca- CAM binds to the CNG channel reducing its affinity for CAMP
the extrusion of Ca through the activation of Na/ Ca exchange proteins
longer lasting adaptation mechanism
CO/cGMP, NO
coding at the ORN
individual odor receptorws expressing the same gene are dispersed throughout the olfactory epithelium but the axons of the receptors converge on 1 or 2 glomeruli in the olfactory bulb
what depicts one molecular feature
1 receptor
what are the primary sensory neurons that generate action potentials in the nose
olfactory receptor cells
life span of olfactory receptor cells
30-60 days
what can detect multiple odors sharingthe same molecular feature
1 receptor
what is all receptors encoding the same molecular feature
1 glomerulus
what does one odor activate
several glomeruli
what do different odors activate
distinct patterns of glomeruli
what do distinct pattern of flomeruli carry
distinct odor info to the cortex- chemotropic odor map
where are glomeruli
in the olfactory bulb
what contains the first order neuron axons that carry infor about one particular component of scents
glomeruli
what do the glomeruli neurons synpase with
mitral cells that refine the smell sense and relay it to the brain for further processing
what are the two routes from the OB
subcortical route
thalamo cortical route
regions of the limbic system- medial sides of temporal lobe (primary olfactory cortex)
subcortical route
route for conscious perception of smell and fine discrimination of smell
thalamo cortical route
what coding do olfaction at cortical neurons follow
population coding
VNO
vomeronasal organ
what is the VNO
accesory olfactory bulb pathway for pheromone detection
what pathway is more restricted (amygdala and hypothalamus) than the main olfactory system
the VNO
are sexually dimorphic and likely involved in mating preferences
VNO pathways in mamals
evidence for VNO existence in humans
not clear but sexually dimorphic nuclei are present in olfactory related structures
what system does the olfactory system interact with
the immune system
what molecules does the immune system use to inteact with the olfactory system
MHC moelcules that detect distinct odor in urine that can be detected by mice
leads mice to mate with distantly related mice rather than closely related mice if confronted with multiple potential mates to prevent defects associated with in breeding
