Compare the neural mechanisms of smell and taste

Sanjay Manohar, Oxford 2017


extraordinary sensitivity
chemoception evolution old - food, defensive, social, navigation, mating
reward; drive appetite etc
pleasantness ~ 1/quantity
obesity; tax, education

Smell Anatomy

 - naris, turbinates, palate, cribriform. obstructive apnoea
   10m neurons. largest gene superfamily ~300 genes
   clonal map: lineage correlates with glomerular choice. broad and narrow range.
   thin dendrites, thru cribriform.
   1000 glomeruli: synapse on Mitral, periglomerular, tufted cells.
   granule cells - GABA
   medial system - anterior commissure, olf tubercle, septal nn
   lateral system - piriform cx (bypasses thalamus!), 
    also entorhinal, hippoc, amyg; newer: -> MDthal, insula OFC
    POMC / NPY arcuate hypothal

Smell relevance:

   anosmia - PD. glomeruli lost with age. head trauma
   olfactory aura.
   pheromones, vomeronasal organ?

   cell turnover
   mucus bowman's glands antibodies, odorant binding proteins
   Gs-cAMP-Ca = action potential. 
    -> amplification
   ligand gated salt / sugar; other GPCR too
    -> adaptation, amplification
   neural processing; labelled lines
     -> lateral inhibition, deconvolve the broad receptor sensitivity


 - facial, glossopharyngeal -NTS - gustatory thalamus - insula
 - hydrophilic, nonvolatile.
 - foliate, fungiform, filiform, circumvallate papillae
 - receptors 2 wk turnover. microvilli, ATP/5HTergic.
 - sweet/umami/bitter: TRPM5 receptors Gq/Na -> GLP1,NPY (autocrine)
 - sour/salt: TRPP receptors/Ca -> 5HT, ACh, NA, gaba at synapses