NEUR30003 Lecture Notes - Lecture 10: Visual Cortex, Receptive Field, Enteric Nervous System
10 May 2018
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Lecture 10
• Gustation - taste
• Olfaction - smell
• Taste and smell create flavour (nature driving force behind appetite)
• Also use smell as key element in reproductive behaviour
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• Flavour - sensory experience of food and drink; dominated by smell and taste (but
includes texture, appearance, temperature, pain [chilli, pepper - active ingredient is
capsaicin], fat)
• Chilli is noxious stimuli
• 6 defined tastes - salt, sweet, fat, umami, sour, bitter; but many have subtypes (bitter
[critical element of broccoli and other veges, cruciforous veges] and sweet)
• Umami - monosodium glutamate (MSG), acidic amino acid, basic flavour ingredient
of chicken, glutamate is essential amino acid, every animal protein taste similar
• Fat and umami modify responses to other tastes, modify flavour
• Humans are capable of overcoming aversive effects in order to obtain good
outcomes for themselves - bitterness of caffeine
• Smell - human can detect more than 2000 different odours, each odour with own
receptor molecules
• Animal pheromones - increase attractiveness
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• Both olfaction and taste contribute to flavour
• Food/drink in mouth can activate taste (gustatory) afferents and olfactory afferents -
olfaction via diffusion of volatile odorants into nasal cavity
• Taste receptors on tongue in mouth
• In nose: olfactory epithelium (surface layer of nasal mucosa, where odours are
detected)
• Two are connected by air spaces in front but equally odours can and do reach
olfactory epithelium from within mouth going back up airway passages
• Move content around mouth to get maximum effect
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•
• Taste is the result of the activation of series of receptors in surface of tongue - those
receptors are localised within taste buds (particular structures in tongue, easy to
detect, quite large)
• Taste buds - are collections of taste-receptive cells (made up of 3 different classes of
modified epithelial cells)
• Apical end - epithelial cells are polarised cells with apical surface (in contact with
outside) and basolateral surface (inside body, where communication occurs to
nervous system); these cells are not neurons (sensory structures but not neurons)
• Each cell (apical end) have at their base - innervated, get terminal of primary afferent
neurons that are part of the gustatory pathway
• Taste activation of taste cell → leads to activation of neurons → triggers signals to
go back to brain
• Papillae are taste sensitive structures
• Usually have 2000-5000 taste buds (each has 5-30 taste cells), not as big system as
retina
• Taste cells turn over in about 2 weeks, characteristic feature of epithelial cells
• Unknown how olfactory axons decide what to end on when old taste cell dies and
new taste cell develops - what leads to connections between the two
• Olfactory axons themselves are tuned to the particular version of responsiveness
• Axon that responds to salt will not all of a sudden want to be innervating taste cell
that is sweet
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Document Summary
Lecture 10: gustation - taste, olfaction - smell, taste and smell create flavour (nature driving force behind appetite) [reduced more dramatically by acetate (vinegar), citrate compared to inorganic acid of equivalent ph such as hydrochloric acid, sulphuric acid]; lead to block of a potassium channel in membrane [depolarises cell opening of calcium channels . Nt release: closing potassium channel has same effect as opening other cation channels (does it more slowly, sweet and umami have more than one receptor, major classes include heterodimer g protein coupled receptors (t1r2/t1r3 sweet; T1r1/t1r3 umami: receptors coupled to phospholipase c and hence to depolarizing mechanisms, t1r1 - receptor for capsaicin, t1r1/t1r3 receptors respond to glutamate, enhanced by inosine. [where many peripheral pathways end] on to many subnuclei of thalamus primary gustatory cortex olfactory regions associated with flavour: gustatory (taste) info ends up going through medulla [involved in autonomic function]
