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Neuronal networks and behaviour summary chemical senses
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This document contains a summary of the chapter “chemical senses” of the course neuronal networks and behaviour.
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Chemical senses chapter 15Olfaction is the oldest evolutionary system, we use it to detect Olfactory epithelium and anosmia
danger when there is for example smoke or fire, eating (taste), The olfactory receptor cells are embedded in the epithelium and
parenting, and social interactions (pheromones). Even bacteria use have long cilia that are packed with receptors that detect odours.
it for chemotaxis, where they can sense their environment by There are also stem cells present in the epithelium that can
detecting chemical cues. replace the receptors eventually. There are also some supporting
cells in the epithelium and glands for mucus production.
The olfactory system Olfactory epithelium can be easily damaged, but it can
Odorants are chemicals that we can smell, it is filtered by the regenerate within a few days. This happens when you get sick
hairs and cavities in the nose. The olfactory sensory neurons in and you cannot smell anymore, but the smell returns.
the nose are embedded in the olfactory epithelium. The olfactory Anosmia is when the whole epithelium layer comes off and all
neurons themselves are short-lived (30-60 days) and are replaced connections are destroyed. When you recover from this it is
by the basal stem. possible that the connections did not grow back normally and
The odorants enter the nasal cavity and diffuse into the mucus. have to be made again.
The olfactory sensory neurons are located in the cribriform plate
above the nasal cavity. The olfactory neurons in the cribriform
plate can detect the odours and send the information to the
olfactory bulb. Since the neurons are epithelial cells, the cells
can be renewed quickly.
Olfactory receptor, 7 transmembrane receptor
Organization of the olfactory system
After the information arrived in the olfactory bulb, the
information travels via the olfactory tract to the olfactory bulb
targets, which include the pyriform cortex, olfactory tubercle, Odorant receptors
amygdala, and entorhinal cortex. The amygdala is involved in To recognise 10000 different odours there is a large family of
emotional memory. After this, there are second target places, genes for olfactory receptors, which is about 3% of all our
which include: the orbitofrontal cortex (involved in higher order genes!
emotional processing, such as motivation, thalamus, hypothalamus Each odorant receptor neuron type is localised in one of the four
(hormones), hippocampal formation (memory, and position in the zones in the olfactory epithelium. Also, each neuron expresses
environment/navigation/location in space). only one type of odorant receptor, but all the neurons that
express the same receptors are located in the same zone.
Response of olfactory receptor neurons to odorants
3 cells are exposed to 3 different odours, cell 2 responds to
Activation during the presentation of olfactory stimuli odour 3 and a little bit to 2, so there is a combinatorial effect.
Cell 3 responds to all 3 odours and some cells respond to
combinations of different odours.
The olfactory bulb in rats takes up more space compared to
humans, which means that rats rely more on the olfactory system.
Though, humans can still detect odours at very low
concentrations (10 molecules per billion), and trace objects in
space using the olfactory system.
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