Practical 2 Flashcards
what do taste receptors signal?
nutritional value
the nose
Odors as volatile components of chemical substances
- Aliphatic
- Aromatic
- Terpenes
- Amines
- Heteroaromatics
- Sulfur compounds:
example of sulfur compounds
rotten smells
garlic
thousands of smells and lots of diff molecules
Optical isomers of terpenes may elicit completely different sensations
Structurally dissimlar odourants can elicit the same sensation
what are natural odours?
blends of many single odourants
natural odours
Gas chromatographic profile of a guinea pig scent mark. Each peak is an odorant of particular strength.
Scents:
- Banana fruit ~ 400 volatile compounds
- Rose - ~600
- Coffee - ~ 800
How many scents does a nose discriminate and how does it deal with scent bouquets?
how are odours sensed?
- odourants bind to receptors
- olfactory receptor cells activated and send electric signals
- signals relayed to glomerulli
- signals transmitted to higher regions of brain
how many olfactory receptors do we have?
Olfactory receptors are sensitive to particular sets of odours, but among those there are one or a few odours to which they are most sensitive (highest affinity of the receptor molecule in the receptor cell membrane for binding the preferred type of odour).
Each receptor type expresses only one type of receptor molecules.
Humans:
- 350 receptor types
Mice:
- 1000 receptor types in ~10 million receptor cells (converging on ~2000 glomeruli)
similarity between odour recognition and colour vision
Olfactory receptors specialise on a subset of physical stimuli.
As with colour, several receptor signals are combined in combinatorial manner to code odour identity
difference between odour recognition and colour vision
Odours differ in more than one dimension (chemical structures).
Many receptors contribute to a complex combinatorial code for each odour sensation
olfactory pathways in the human brain
In humans, a sheet of cells called the olfactory epithelium lines the dorsal portion of the nasal cavities and adjacent regions, including the septum that separates the left and right nasal cavities.
Within the 5–10 cm2 of olfactory epithelium that we possess, three types of cells are found: supporting cells, basal cells, and about 6 million olfactory receptor neurons.
Each olfactory receptor cell has a long, slender apical dendrite that extends to the outermost layer of the epithelium, the mucosal surface.
There, numerous cilia (singular cilium) emerge from the dendritic knob and extend along the mucosal surface
At the opposite end of each bipolar olfactory receptor cell, a fine, unmyelinated axon, which is among the smallest-diameter axons in the nervous system, runs to the olfactory bulb.
If the olfactory epithelium is damaged, it can be regenerated and will properly reconnect to the olfactory bulb.
Olfactory cues arrive at the orbitofrontal cortex.
olfactory cues combine with taste
Primary gustatory cortex (AI/FO):
Retronasal olfaction:
Orthonasal olfaction:
Orbitofrontal cortex receives input from taste, temperature, touch and smell
diffs in perception of everyday odours
Primates and humans were traditionally considered to be ‘microsmatic’, e.g. with a less developed sense of smell.
Recent studies however show high sensitivity for many odourants that compares or is even better than that of ‘macrosmatic’ animals (dog, rat).
Humans seem to rely strongly on odours, e.g. determining the identity of objects, their edibility
aliphatic
alcohols, aldehydes, acids, esters
aromatic
benzoids, phenols, phenylpropanoids
