The Chemical Senses

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What are sensory organs?
Structure specialised for detecting particular types of stimuli.
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What are sensory receptor neurons?
Converts stimuli into electrical signals.
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What is sensory transduction?
Conversion of stimulus energy into electrical signals.
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What is the sensory/ afferent pathway?
How information travels from sense organ ---> brain stem ---> tectum ---> thalamus ---> cortex.
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Why are neurones described as specialist?
Because of its parent, environment and education, a neuron will be particularly interested in one type of information.
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What does specialisation of sensory cells depend on?
The type of receptor.
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What are afferent/ sensory nerves?
Carry information from sensory receptors towards the brain.
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Why is olfaction special (2)?
Approximately 4% of our genes code for olfactory sensory receptors, the cerebrum evolved initially for olfactory processing.
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What are some features of the olfactory system (4)?
Evolved much before the neocortex, develops from tissue in the olfactory bulb, basic to brain functioning, strongly linked to the limbic system meaning that olfactory memories tend to be the most emotionally intense.
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Where does olfactory information go to?
The orbitofrontal cortex.
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What is the olfactory organ?
The nose.
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What is the purpose of mucus?
To capture odorants and allow them to diffuse onto the cilia. It also protects the cilia and removes old odorants.
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What are olfactory receptor neurons (ORNs)?
Produce action potentials and send information along axons. Replaced approximately every 28 days.
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What is the process of olfaction using G-protein receptors?
Odorant molecule binds to receptor protein ---> Receptor-odorant complex activates G-protein, which combines with one GTP molecule, displacing GDP ---> G-protein α subunit dissociates and activates adenyl cyclase, producing cAMP --
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*CONTINUED*
-> cAMP activates gates cation channels. Na+ and Ca2+ enter cell, depolarising it and inducing Cl- channels to open, leading to further depolarisation ---> Receptor protein returns to unbound state.
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What is amplification in the context of olfaction?
If lots of cAMP is produced, many channels become opened. Even small amounts of odorant can produce an action potential.
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How can different people smell different things?
Due to differences in the genes using to code receptors of ORNs.
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How are ORNs organised in the olfactory epithelium?
ORNs in the same family are grouped together, and ORNs with the same type of receptor project to the same glomerulus.
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What is a glomerulus?
A cluster of nerve endings.
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What do mitral cells synapses do?
Project information from glomeruli to piriform cortex.
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Where are taste buds found?
On the papillae.
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What is the purpose of saliva?
To carry tasteants through taste pores into taste buds.
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What are the five types of taste and nutritional categories?
Sour, bitter, sweet, umami, and salty.
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What does bitterness generally indicate?
Toxins.
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Why are bitter receptors generally at the back of the tongue?
To trigger reflexes to prevent food from being swallowed.
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What are salty and sour tastes triggered by?
An influx of tastant cations through amiloride-sensitive Na and H sensitive TRP channels respectively. This causes depolarisation.
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What are bitter tastes triggered by?
A family of G-protein coupled receptors.
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What type of receptors do sweet/ umami tastes use?
Combinations of two G-protein coupled receptors.
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How are primary afferent neurons organised?
In three cranial nerves that terminate in the medulla.
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How is information from different types of tastes carried to the brain?
By different subsets of neurons and activate different populations of neurons in the cortex.
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What are the roles of taste receptors (2)?
To monitor nutritional state, to aid in long-term learning by providing reward signals.
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Card 2

Front

What are sensory receptor neurons?

Back

Converts stimuli into electrical signals.

Card 3

Front

What is sensory transduction?

Back

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Card 4

Front

What is the sensory/ afferent pathway?

Back

Preview of the front of card 4

Card 5

Front

Why are neurones described as specialist?

Back

Preview of the front of card 5
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