Chemical Senses Flashcards
What are the chemical senses?
taste
smell
What is the importance of chemical detection (Chemoreceptors)?
Finding food
Finding mates
Avoiding dangerous substances
Homeostasis
What are the submodalities of Taste?
salt, sweet, sour, bitter, umami
What is the distribution of taste cells?
distributed all over the tongue (no absolute regions) however some areas have a higher density of taste cells for a specific modality
what are taste buds?
groups of taste cells
Where are taste buds found?
tongue, palate, pharynx
what are taste cells not?
sensory neurones (they look like a synpase but they aren’t a synapse because they have no neurone)
What are some properties of tase cells?
Taste receptors (not neurones)
Constantly replaced (every 2 weeks)
Have various transduction mechanisms depending on the submodality type
What happens when a chemical binds to a taste cell?
- chemical binds
- transduction occurs causing a receptor potential
- depolarisation
- voltage gated calcium channels open
- calcium entry
- neurotransmitter released
- excites sensory neurone
- action potential
How is salt detected?
- sodium entry causes depolarisation through leak channels
2. if there is a high conc of Na+ it causes an action potential
How is sour detected?
- H+ ions can either enter through TRP
- or H+ block K+ channels causing depolarisation
How are sweet, umami and bitter detected?
- G protein coupled receptors
- subunits are T1R and T2R family
- unique combination of each subunit for each taste
What is the combination of GPCRs for the modality of sweet?
T1R2 and T1R3
What is the combination of GPCRs for the modality of Umami?
T1R1 and T1R3
What is the combination of GPCRs for the modality of Bitter?
T2R and T2R
What is the central gustatory (taste) pathway?
gustatory sensory axons (1’ neurone)
cranial nerves
Synapse in brainstem (gustatory nucleus) (2’neurone)
Synapse in thalamus (3’ neurone)
primary gustatoty cortex
What are the secondary pathways for taste and what are they used for?
-medulla
responsible for salivation and swallowing
-hypothalamus
for satiety (fullness) palatability (how nice it is)
What does the neural coding of taste do?
Comparison from all taste inputs
Gives a general taste of substances
Which is more sensitive, taste or smell?
Smell is much more sensitive than taste
Where are the smells receptors?
small receptors in the olfactory epithelium in the nose
Are olfactory cells neurones?
yes
How many types of receptor does each olfactory cell have?
1
Can receptor molecules bind to more than one odourant?
yes
What are some properties of olfactory cells?
They are neurones
replaced every 4-8 weeks
1 type of receptor molecule per olfactory cell
Each receptor molecule can bind to a range of odorants
How are smells detected?
Signal transduction
- Single mechanism for all receptors
What is a key speciality of olfactory neurones?
Rapidly adapting and therefore will lose sensitivity of an environment the longer the cells are exposed to it.
how is an action potential generated in an olfactory cell to detect smell?
Odorant binds to receptor
G-protein mediated events
intracellular cascade
Na/Ca channels open
depolarisation (receptor potential)
passes threshold
Action potential
What is the olfactory bulb?
Location of the 1st synapse of the primary neurone.
Neurones of a similar range of molecules synpase close together in the glomerulus.
What is the central olfactory pathway?
olfactory neurones (1’ neurone)
olfactory bulb (2’ neurone)
olfactory cortex
Where can the olfactory pathway lead to after the signal has reached the olfactory cortex?
Limbic areas (associate information with emotion eg. smell of a place)
MD thalamus to orbitofrontal cortex (recognition and combining smell and taste)
