The chemical senses Flashcards
What is taste also known as?
Also known as gustation
What are the 5 basic tastes?
- Umami
- Sweet
- Bitter
- Sour
- Salt
What can contribute to the perception of flavor?
-Texture and appearance can contribute to out perception of flavour
What combination provides us flavor?
A combination of taste smell and touch provide us flavor
What are the organs of taste?
- Foliate papillae
- Vallate papillae
- Fungiform papillae
What are within our papillae and what reside in them?
WIthin the papillae there are ridges and valleys in which out tastebuds reside
What are there within each individual taste bud?
Within each individual tastebud there are segments of taste cells and basal cells
What do basal cells replace and do?
Basal cells mature and replace dead taste cells and then the basal cells used are replenished
What do microvilli have in taste cells?
Microvilli in taste cells have the receptors to detect the different tastes
By what mechanism is saltiness and sourness mediated by?
Saltiness and sourness mediated by ion channel mechanisms
By what mechanism is bitterness, sweetness and umami mediated by and via what receptors?
Bitterness, sweetness and umami mediated by GPCR mechanism via T1 and T2 taste receptors
What is a major component of salt?
Na+
Steps involved in the taste transduction of saltiness
- Na+ passes through Na+ selective channels in microvilli down its concentration gradient
- This depolarises the test cell, activating VGCC’s
- This results in vesicular release of neurotransmitter(Serotonin) and gustatory afferent activated
What is H+ the determinant of?
H+ is the determinant of acidity and sourness
Steps involved in the taste transduction of sourness
- H+ can pass through the same Na+ selective channels in microvilli that mediate saltiness down its concentration gradient
- H+ also blocks selective K+ channels
- Both these actions depolarise the taste cell, activating VGCC’s
- Results in vesicular release of neurotransmitter(serotonin) and gustatory afferents are activated
What is bitterness detected by?
Bitterness is detected by T2 taste receptors of which there are over 30 types
Steps involved in the taste transduction of bitterness
T1/T2 receptors are Gq coupled
- PLC converts PIP2 to IP3+DAG
- IP3 intracellularly activates a type of Na+ ion channel and releases Ca2+ from the ER
- Both these actions depolarise the taste cells, activating VGCC’s
- Results in vesicular neurotransmitter release and activation of gustatory afferents
What is sweetness detected by?
Detected by a dimer receptor formed from T1R2+T1R3
Steps involved in the taste transduction of sweetness
Same signal transduction mechanism as bitterness
What do taste cells express to ensure we don’t mix up taste?
Taste cells express either bitter, sweet or umami receptors so we don’t mix up the taste
What is umami detected by?
Detected by a dimer receptor formed from T1R1+T1R3
Steps involved in the taste transduction of Umami
Same signal transduction mechanism as bitterness and sweetness
What is the central taste pathway?
Anterior tongue(CNVII), Posterior tongue(CNIX) and Epiglottis(CNX) transmit information to the gustatory nucleus in the medulla. The information is then transmitted to the ventral posterior medial nucleus and the the gustatory cortex
What is smell also known as?
Also known as olfaction
What are pheromones?
Are chemical signals that are smelt
What are the organs of smell?
- Olfactory bulb
- Cribriform plate of ethmoid bone
- Olfactory tract
- Olfactory epithelium
What do we smell with?
Smell with olfactory epithelium
What is the olfactory epithelium?
Olfactory epithelium are dendrites of olfactory cells
What does the olfactory hairs(cilia) have?
The olfactory hairs (cilia) have a water base containing sugars, enzymes, antibodies and odorant binding proteins
How do olfactory receptor neurons function?
- Odorant molecules bind to odorant receptor proteins on the cilia
- Odorant receptor is Golf coupled and is activated
- Adenylyl cyclase activation increases cAMP formation
- cAMP activated channels open, allowing Na+ and Ca2+ influx
- Ca2+ activated chloride channels open enabling Cl- efflux
- This leads to depolarisation of the cell
How many olfactory receptor proteins are found in the human genome?
350 olfactory receptor proteins found in the human genome
What may olfactory receptor cells express?
May express only one receptor protein
What does each receptor protein respond to?
Each receptor protein responds to odors to a greater or lesser extent
What are smells differentiated due to?
Smells are differentiated due to population coding
What are temporal and spatial cues seem important for?
Temporal and spatial cues seem to be important for decoding olfaction
What is the central olfactory pathway?
Olfactory receptor cells(CN1) to the olfactory bulb. From olfactory bulb to the followig: -Frontal cortex -Hypothalamus amygdala -Hippocampus
NB: Doesn’t have to go via thalamus before anywhere else
