The chemical senses Flashcards
What is the gustatory system?
Taste
What is the olfactory system?
Smell
What are the chemical senses?
Olfactory and gustatory system
What are the functions of the chemical senses? (3)
- Identify food sources
- Avoid noxious substances
- Find a mate/mark territories (pheromones)
What are the 5 basic tastes?
- Salty
- Sweet
- Sour
- Bitter
- Umami (savoury)
Why do we crave salt?
Required for many physiological processes e.g. neurotransmission
What is our natural preference to sour tastes and why?
- Avoid
- High acidity (H+) could cause damage to GI tract
Why do we crave sugars?
Required for energy and growth
Which is the first flavour we learn to enjoy?
Sweet
What is our preference to bitter tastes and why?
- Avoid
- Toxic substances and poisons are often bitter
What is the umami taste related to?
- Amino acids, specifically glutamate
- MSG added to foods (monosodium glutamate)
Why do we crave umami tastes?
Amino acids needed for protein synthesis, neurotransmission etc.
What is the chemical in chilli which makes it taste spicy?
Capsaicin
How is capsaicin detected?
- Receptors for capsaicin on the tongue
- Same receptors which detect heat on the skin
What are the taste organs? (5)
- Tongue
- Cheeks
- Soft palate
- Pharynx
- Epiglottis
What is the name of the structures on the tongue which contain taste buds?
Lingual papillae
What do the taste buds contain?
Taste cells
What are the 4 types of lingual papillae?
- Filiform
- Foliate
- Fungiform
- Circumvallate
Where are the filiform papillae located?
Middle of the tongue
What is the function of the filiform papillae?
Detect texture (no taste buds)
Where are the circumvallate papillae located?
Back of the tongue
Where on the tongue is the majority of taste detected?
- At the back by the circumvallate papillae
- Contains the most taste buds
Where are the foliate papillae located?
Round the sides of the tongue
Where are the fungiform papillae located?
Front of the tongue
Where are the taste buds on the fungiform papillae?
Top
What is the structure of a taste bud?
- Contains taste cells
- Microvilli at the apex of the taste cells pointing into the taste pore which is in contact with saliva and food, where the taste receptors are
- Synapse to the gustatory afferent neurones at the base of the taste bud
How many taste buds are there?
2000-5000
How many taste cells are there per taste bud?
100
Which receptor detects salty flavours?
ENaC and an unknown mechanism
What kind of receptor is ENaC?
Ionotropic
Which receptor detects sour flavours?
OTOP1
What kind of receptor is OTOP1?
Ionotropic
What kind of receptor perceives salty tastes?
Ionotropic
What kind of receptor perceives sour tastes?
Ionotropic
What kind of receptor perceives bitter tastes?
Metabotropic
What kind of receptor perceives sweet tastes?
Metabotropic
What kind of receptor perceives umami tastes?
Metabotropic
Which receptors detect bitter tastes?
T2Rs
What kind of receptor is T2R?
Metabotropic
What are the subunits in the receptors for sweet tastes? (2)
- T1R2
- T1R3
What are the subunits in the receptors for umami tastes? (2)
- T1R1
- T1R3
Which subunit do the receptors for sweet and umami have in common?
T1R3
How many types of taste can each taste cell respond to?
One e.g. sweet taste cells only respond to sweet stimuli
How many types of taste can each taste bud respond to?
Many i.e contains many taste cell types
How do taste cells transmit information?
- Chemical stimulus binds to receptor at apex of cell (transduction)
- Causes depolarisation of taste cell
- Causes influx of calcium
- Neurotransmitter released across synapse to gustatory afferent neuron
What are the major anatomical components of the olfactory system? (4)
- Olfactory cavity
- Olfactory epithelium
- Olfactory bulb
- Olfactory cortex
How are odorant stimuli sent to the brain?
- Diffuse into the olfactory cavity and dissolve into a mucus layer on the olfactory epithelium
- Signal transduction occurs on the cilia of the receptor cells
- Graded potentials travel up the dendrite to the axon initial segment where the may trigger action potentials
- Receptor cells send axons through the cribriform plate to glomeruli in the olfactory bulb and to secondary afferent neurones
What is the olfactory epithelium?
Location of the olfactory receptor cells
What kind of cells are olfactory receptor cells?
Neurones
Which part of the nervous system is the olfactory bulb classed as?
CNS
Which part of the nervous system is the olfactory epithelium classed as?
Peripheral
What is the area of the human olfactory epithelium?
10 cm^2
What is the area of the dog olfactory epithelium?
170 cm^2
Are olfactory receptor axons myelinated or unmyelinated?
Unmyelinated
Which neurones are regularly replaced?
Olfactory receptors
How many odorant receptor proteins do humans have?
350
How many types of odorant receptor proteins are there per olfactory receptor cell?
One
How many odorants can each odorant receptor protein bind to?
Multiple
What allows us to distinguish specific odours?
Unique combinations of receptor activation by an odorant
What kind of receptors are odorant receptor proteins?
G-protein coupled
Which G protein are odorant receptor proteins coupled to?
Golf (olfactory G protein)
What happens when an odorant receptor protein is stimulated?
- Activates Golf
- Activates adenylyl cyclase
- Increases cAMP levels
- cAMP binds to channels which open and allow influx of Na+ and Ca2+
- Causes depolarisation
- Ca2+ gated Cl- channels open and Cl- LEAVES cell causing further depolarisation
What is the effect of a larger stimulus on action potentials?
Increased frequency (APs don’t change size)
What happens at the glomerulus in the olfactory bulb?
Receptor cells expressing the same type of odorant receptor protein converge at the same glomerulus
What is the olfactory cortex?
Area of the brain which perceives smell
