Taste and Smell

Taste and Smell

1. Taste

   • 5 basic tastes
     • Umami
     • Sweet
     • Bitter
     • Sour
     • Salt
   • Taste buds
     • Create neural signals
       • Sent via cranial nerves
     • Embedded in papillae
     • Contain taste receptor cells
   • Coding of taste quality
     • Labelled lines
       • Each taste fibre carries a particular taste quality?
     • Patterns of activity across different taste neurons?
     • Examples of both in other senses
   • Genetic variation
     • Arthur Fox (1931)
     • Dennis Drayna (2003)
     • Supertasters
       • Different genes for PROP receptors
       • More taste buds
     • Hardwired taste preferences
       • Evidence from babies
       • People can be desensitised to chilli peppers
         • Only humans eat it!

2. Smell

   • Smelly molecules
     • Small
     • Volatile
     • Hydrophobic
   • Physiology
     • Air flow through nose disrupted by turbinates
       • Contacts with olfactory epithelium which odourants stick to
     • Nose has a cycle time of three hours during which different nostrils have different flow rates and smell different things
     • Anosmia
       • Cribiform plate moved backwards (usually because something has hit you in the front of your face)
     • Odours bind to olfactory cilia
       • Part of the OSN
         • Each OSN has a single type of odour receptor
         • 5 million of these!
         • Fire once 8 binding sites are filled
         • Sends to olfactory bulb (not thalamus)
       • Lock and key model
         • But it is difficult to predict smell from shape...
       • Vibrational sensitivity?
     • 300 receptor types
       • Generate patterns of activity in entorhinal and piriform cortices
         • Associate code pattern with object
   • Human pheromones?
     • VNO
       • Doesn't function in adult humans (but it does in foetuses)
     • HLA
       • MHC is present in humans as a result of this gene complex
     • Androstadienone
       • Metabolite of testosterone
   • Blindsmell
     • Brain response to concentrations below perceptual threshold?
     • Smell of tears
       • Chemosignal