Sensory Two - Olfactory and Taste Flashcards
What does the ability to discriminate two point touch rely on?
The receptive field or receptors and their density.
Is receptor density uniform throughout a sensory organ?
No it is not
Why are receptors in a sensory organ not uniform?
They may be localized to give higher definition
How is intensity of a stimulus encoded generally?
BY the number of receptors activated and the frequency of their firing.
Where does all sensory information go to?
The thalamus before it is relayed
What do afferent pathways in sensory systems carry information about?
The detected stimulus (single type of stim, not bundled together)
Describe the neuron structure between the receptor and the cortex?
Polysynaptic pathways
What do chemical sense allow?
Identification of food, noxious stimuli and mates
What are two human sense that are chemoreceptive?
Olfaction
Gustatory
Where are the receptors located for gustation?
Chemoreceptors are localized to papillae
Gustation and olfaction, differ how?
They are separate pathways but compliment one another
Whats the density of taste receptors?
50-150 taste receptors per a taste bud.
Thus 2000-5000 taste receptors per a tounge
How do taste receptors on each papillae respond to different concentrations of stimuli?
Very selective at low concentrations, less so at higher ones.
The taste chemoreceptors are found where on the pipillae?
In taste pores and have a turnover rate of around 2 weeks.
What to gustatory chemoreceptors synapse with?
They synapse with gustatory afferent axons.
Whats unique about the tongue with regards to taste specificity?
The tounge is divided into five areas of taste. They somewhat overlap as no clear border is formed, like 99% of things in bio
What are the three types of gustatory receptor cells and what taste do they detect?
Type One: Salty
Type Two: Sweet, Better, Umami
Type Three: Sour
Salty and sour (acid) use what sort of receptors?
Ion channels
Describe the transduction of salt taste into perception of salty goodness?
Salt (Na) influxes through the ion channel, depolarizing the membrane causing Ca influx through voltage gated Ca channels and thus neurotransmission onto the gustatory afferent axon.
Describe the transduction of sour (acid) taste into perception of sourness?
Acid (H) influxes through the ion channel, inhibiting K efflux thus depolarizing the membrane causing Ca influx through voltage gated Ca channels and thus neurotransmission onto the gustatory afferent axon.
What sort of receptors do Sweet, Bitter and umami use?
GPCRs
What does chemointeraction with GPCRs result in?
The activation of phospholipase C, IP3 and or other secondary messangers.
Resulting in the opening of Na channels, depolarisation and thus Ca channels open and neurotransmission occurs
What GPCR specifically does bitterness use?
T2R (30 types)
Cant distinguish bitterness only that it is bad
What GPCR specifically does sweetness use?
T1R
- Requires two T1R receptors together (T1R2 and T1R3) together to detect sweetness
What GPCR specifically does umami use?
Umami is the detection of amino acids
Requires two T1R receptors (T1R1 and T1R3)
Are the gustatory afferent axons the same for every taste receptor?
No they are specific to the taste
Where does gustatory information project to in the brain?
Firstly to the ventral posterior medial nucleus of the thalamus which relays it the the cerebral cortex
Polysynaptic pathways for gustation are found in which cranial nerves?
7 (facial)
9 (Glossopharyngeal)
10 (vagus)
All cary gustatory fibres which innervate the NTS then the Thalamus
What areas of the cerebral cortex are dedicated to gustation?
Frontal operculum and insular cortex
What sort of receptors are olfactory receptors?
GPCRs
How many odours are each receptor specialized to?
One or Two
How is the olfactory organ organized?
The olfactory organ located in the upper nose is organized into zones which express a particular subset of receptor genes
Describe the olfactory pathway
Olfactory receptors Olfactory Bulb Several cerebral targets before all innervating either the: - Thalamus - Hypothalmus - Orbitofrontal cortex
Any receptor that is continuosly stimulated does what?
Adapts and stops firing i.e why bad smells cant be smelt after a while. In the case of light source, they fatigue and stop firing.
Similar olfactory receptors do what?
Innervate the same glomeruli in the olfactory bulb
Increasing the concentration of odour does what to the olfactory receptors?
Increases their rate of firing
What is a unique property of the olfactory organ caused by its structure?
It may also be directional
