The Chemical Senses Flashcards
What do chemoreceptors in the arteries of the neck measure?
CO2/O2 levels in our blood
What do nerve endings in skin/mucus membranes warn us of?
Chemical irritants
What do sensory nerve endings in muscle respond to?
Acidity
What are the innate taste preferences?
We enjoy sweet and avoid bitter flavours
What does gustation mean?
Taste
What are the 5 basic tastes?
Salt, sweet, sour, bitter and umami
What (apart from taste) plays an important role in flavour perception?
Touch, texture, smell and temperature
What are the organs of taste?
Tongue, palate, epiglottis, pharynx and nasal cavity
What does the palate and epiglottis contain that enables them to be an organ of taste?
Taste buds
How are the pharynx and nasal cavity involved in taste?
Odours can pass via the pharynx to the nasal cavity and are detected by the olfactory receptors
How many taste receptor cells do each taste bud contain?
50-150
What are taste pores?
The chemically receptive end of the taste cell
What are taste buds surrounded by?
Basal cells (taste cell precursors) and gustatory afferent axons
How do taste receptor cells transmit gustatory information?
Form synapses with gustatory afferent axons
What are the two mechanisms of taste transduction and which tastes work by what?
Ion channel mechanisms (salt, sour)
GPCR via T1 and T2 taste receptors (bitter, sweet and umami)
What is the salt taste mainly derived from?
Sodium
How does sodium cause a salty taste?
Ions pass through the Na+ selective channels down the conc gradients
This depolarises the taste cell, activating voltage gated calcium channels
Causes the vesicular release of neurotransmitter, activating gustatory afferents
What do high concentrations of salt activate?
Bitter and sour taste cells
What are the determinants of acidity and sourness?
Protons
How do we taste sourness?
Protons pass through the channels, bind to and block potassium selective channels. This leads to depolarisation of the taste cell, activating voltage gated sodium and calcium channels to open
What are bitter substances detected by?
25 T2Rs
What are sweet substances detected by?
T1R2 and T1R3 proteins
What are umami substances detected by?
T1R1 and T1R3 proteins
What is the T2R coupled to?
Gq pathway
What does the Gq pathway do?
Stimulates the enzyme phospholipase C, which leads to the production of IP3
IP3 activates a special type of sodium ion channel and releases calcium from intracellular storage sites
Why don’t we confuse bitter, umami and sweet tastes?
Taste cells express either bitter, umami or sweet receptors not both
What pathway does taste information take to the brain?
Taste cells -> gustatory axons -> gustatory nucleus -> ventral posterior medial nucleus -> gustatory cortex
Where is the gustatory nucleus found?
Medulla
Where is the ventral posterior medial nucleus found?
Thalamus
What three cranial nerves carry gustatory axons to the brain?
VII (facial), IX (glossopharyngeal) and X (vagus)
What are pheromones?
Olfactory stimuli used for chemical communication between individuals
What are pheromones important for (in animals)?
Reproductive behaviours, marking territory and indicating aggression or submission
What is the olfactory epithelium?
Small sheets of cells high up in the nasal cavity
What are the three main cell types in the olfactory epithelium?
olfactory receptor cells, supporting cells, basal cells
What do the olfactory receptor cells do?
Transduction
What do supporting cells do in the olfactory epithelium?
Function to produce mucus, because odorants dissolve in mucus layer before contacting the cilia of olfactory receptor cells
What are basal cells?
Immature olfactory receptor cells that are able to differentiate into mature olfactory receptor cells
What are the olfactory transduction mechanisms?
Odorant molecules bind to odorant receptor proteins in the cilia, which activates an olfactory specific G protein.
Adenylyl cyclase activate increases cAMP formation, which allows sodium and calcium influx
What do odorants generate in the cilia?
Slow receptor potential
Which parts of the brain deal with olfaction?
Frontal cortex, hypothalamus and amygdala and hippocampus
What part of olfaction does the frontal cortex control?
Conscious perception of smell
What part of olfaction do the hypothalamus and amygdala control?
Motivational and emotional
What part of olfaction does the hippocampus control?
Odour memory
What is population coding?
The responses of a large number of broadly tuned neurones are used to specify the properties of a particular stimulus
