Smell - chemoreception

function of smell

• food selection

• mate selection

  • pheromones: smell of animals that attract to mates

receptors of smell in nose

• inhaled air goes through nasal conchae and is sent up to olfactory tract, bulb, epithelium which are what detect odorous chemicals

• bipolar neurons; ciliated dendrites

• Proteins in cilia bind to odors

olfactory reception in nose

chemical binds to receptor protein and then opens up ion channels

olfactory processing

• glomerulus: cluster of neurons that recieve info from the receptor cells with similar selectivities; 1st place of sensory processing

  • olfactory epithelium contains olfactory receptor cells

  • from this it goes to mitral cells

    • abt 25000 receptor cell axons synapsing on abt 25 mitral cells

how smell works

1. odor binds to receptor protein: G-protein coupled

2. Activated G-proteins activates adenylate cyclase to make cAMP

3. cAMP opens Na and Ca channels

4. results in graded depolarization which triggers AP

combonational code for odor

• odorants are coded by combos of olfactory receptors: across fiber patterning

• specific receptors may be part of code for multiple odorants

  • ex: we have 26 different letter in the alphabet, you can have multiple combonations of these letters to create words

    • each word has different meanings tho

the perception of flavor

• perception of flavor comes from the combonation of smell, taste, and other sensations (such as burning a lot of peppers)

• odor stimuli from food in moth reaches olfactory mucosa through retronasal route

• taste of most compounds is influenced by smell

the puzzle of olfactory quality

there are abt 350 functional genes coding for different olfactory receptors in humans: each gene for 1 receptor

• therefore each receptor is best “tuned” to 1 of 1000 different chemical “types”

• what these types are are still not clear nor is how the code gets turned into a “smell”

  • maybe combinational code?