Taste System

what is the transduction mechanism for taste receptors for saltiness?

taste of salt is mostly due to the detection of Na+, saltiness receptors express Na+ channels (amiloride sensitive channels), detect Na+ at low concentrations, however high concentrations of salt can also activate other receptor cells for sour and bitter

what does the umami taste modality involve?

taste of the amino acid glutamate (monosodium glutamate)

where does the tertiary neuron for taste go to and from?

tertiary neuron carries input from the VPM, and connects to the insular cortex

how many bitter receptors are there and to which family do they belong?

30 bitter receptors belonging to the T2R family

how many receptor cells does one taste bud contain?

50-150 receptor cells

where is the taste receptor organ located?

primarily located in the papillae of the tongue, in receptor organs called taste buds, in addition there are receptors located in the palate, pharynx, epiglottis, and nasal cavity

what is the term that means protrusions in the tongue shaped like ridges, or pimples?

papillae

how many taste buds does each papillae contain?

1-100 taste buds

what two cortical regions are primarily involved with taste?

1. insular cortex 2. opercula

which three taste modalities are triggered by organic ions?

1. sweet 2. bitter 3. umami

what are the five basic taste modalities?

1. sweet 2. bitter 3. umami 4. sour 5. salty

what is the neurotransmitter involved with bitter, umami, and sweet taste modalities?

ATP

what kind of receptor protein are taste receptor proteins?

G-protein coupled receptors

attractive tastes trigger what receptor family?

T1R family (R1, 2, 3)

umami receptor cells express which T1R family receptors?

T1R1 and T1R3

what kind of receptor proteins are expressed in umami receptor cells?

T1R1 and T1R3

sweet receptor cells express which T1R family receptors?

T1R2 and T1R3

what kind of receptor proteins are expressed in sweet receptor cells?

T1R2 and T1R3

sweet and umami receptor cells express different combinations of what receptor protein family?

T1Rs

what kind of receptor proteins are expressed in bitter receptor cells?

T2Rs

what does the sour taste modality involve?

acids, vinegar, citrics (triggered by H+ ions)

what does binding of a substance to the chemoreceptor do?

binding of a substance to the chemoreceptor depolarizes the taste receptor, either allowing Ca2+ influx, or causes release of Ca2+ from intracellular stores

poison receptors trigger what taste modality?

bitter

describe how you can distinguish between bitter, sweet, and umami if their receptors activate the same second messenger cascade

bitter, sweet, and umami receptor proteins (G-protein couple receptors) are expressed in different receptor cells, which are connected to different gustatory axons, the bitter, sweet, and umami signals are transmitted preferentially in different transmission lines (parallel processing)

T1R3 is a receptor for what ion?

calcium

what do receptor responses depend on?

depend on the transduction mechanism present on the cell

are the neural pathways for taste primarily ipsilateral or primarily contralateral?

ipsilateral

are taste receptors selective for particular chemicals?

no

what is the sixth debated taste modality?

oleogustus (fatty acids, but transduction mechanisms are unclear at the moment)

where are the chemoreceptors for taste located on the taste cells?

on the apical end of taste cells in the microvilli

where does the primary neuron for taste go to and from?

primary neuron carries input from the tongue to the solitary nucleus (afferent fibers carried in by VII, IX, and X, SVA component)

what does the bitter taste modality involve?

quinine or caffeine, can be detected at nanomolar concentrations, poisonous substances are bitter (triggered by K+, Mg2+, and complex organic molecules)

what does the salty taste modality involve?

salts (triggered by Na+ ions)

where does the secondary neuron for taste go to and from?

secondary neuron carries input from the gustatory nucleus (a special part of the solitary nucleus that processes taste) and projects to the VPM in the thalamus

what is the neurotransmitter involved with sour and salty taste modalities?

serotonin

what is the transduction mechanism for taste receptors for bitter, sweet, and umami?

share the same transduction mechanism, using receptor proteins of the T1R and T2R families (G-protein coupled receptors), and use ATP as neurotransmitter

describe how the tongue responds to the five different taste modalities

some area of the tongue are slightly more sensitive to a particular taste modality (e.g. sweet and salty at the tip, sour on the sides), but there are no areas exclusively dedicated to each taste, the whole tongue is sensitive to all basic tastes

what is the transduction mechanism for taste receptors for sourness?

sour taste is mostly due to the detection of H+ from acids (HCL, acetic acid, etc.), sour receptors express PKD2L1, a special type of K+ channel blocked by H+

what does the sweet taste modality involve?

sugars (fructose, sucrose, etc.)

more than 90% of the receptor cells respond to how many of the basic tastes?

two or more of the basic tastes (receptors are not selective)

can receptors respond more or less selectively to a taste depending on the concentration of the taste?

yes