Chemical Senses (2) Flashcards
Positive chemotaxis is used to what?
find nutrients or locate a mate,
Negative chemotaxis does what?
helps us avoid noxious agents such as rotten smells and food.
Our nervous system codes for chemicals in our environment by using what?
Labeled Line and Population Coding.
What is Labeled Line?
Each chemical is a preferred stimulus which has its own receptor and circuit.
Population Coding (Pattern Coding) is what?
Receptors/circuits not ultimately selective. NS analyzes all chemical responses coming in, compares to pinpoint what chemical stimulus might be.
What are the different Taste cell types?
Receptor cells- modified epithelial, 50-150 per taste bud; Supporting cells develop into receptor cells. Basal cells develop into supporting cells.
What is the innervation of taste cells?
Afferent n. enter buds, end on receptor cells.
Nerves chem synapse on cell, 1:many or many: 1 receptor:nerve; nerves continually remodel synapses on new receptor cell; Receptors degenerate w/o innervation
Most of the tongue is sensitive to all basic tastes. What are the exceptions?
receptor can respond to more than one taste, has a preferred taste at threshold levels; Certain regions are more sensitive to specific basic tastes
Receptor potentials of taste receptor cells are generated where?
microvilli and apical membrane by a tastant.
What does a tasant do?
moves through ion channels or activates a G
protein.
What are the characteristics of a taste receptor potential?
graded, changing (depolarizing or hyperpolarizing) by an appropriate chemical
Action potentials in the cell body of taste
receptor cells lead to what?
increased Ca2+ influx thru voltage-gated membrane channels w/ release of Ca2+ from intracellular stores-> NT released-> synaptic potentials in dendrites of sensory nerves;
How does salty stimuli act on receptor?
tastant mostly Na+ may pass directly thru ion
channels down its concentration; insensitive to voltage; open at rest; inward current causes the membrane to depolarize.
How does sour stimuli act on receptor?
Tastant is H+; permeate channel that mediates the salt taste; inward H+ current, cell depolarizes; H+ ions can bind/block a K+-selective channel. When K+ permeability is decreased, cell depolarizes. 2 processes work together
How does bitter stimuli act on receptor?
several mechanisms: Some bitter tastants bind directly to K+-selective channels and block them or can activate GPC 2nd messenger cascades.
How does sweet stimuli act on receptor?
Sweet molecules bind specific receptor sites (GPCR), activate cascade of 2nd messenger in certain taste cells.
How does umami stimuli act on receptor?
Glutamate activates G-protein-coupled 2nd messenger cascades in certain taste cells; meaty flavor
How is intensity of taste coded?
greater the amount of tastant, the faster the
firing rate of afferent fibers
What is taste pattern coding?
Each taste cell responds differently to four tastants
What is population coding of taste?
responses of 4 taste cells to 4 different tastants; combined in brain to determine
the final taste
What other senses are involved in taste sensation?
vision first, tactile, taste, olfaction, Thermal, irritative, kinaesthetic and auditory patterns
What other than sensory modalities effects taste perception?
adaptation, memory and conditioning; Taste is acquired;
Aguesia results in what?
effects control of feeding and digestion; control of body weight may be difficult
At low concentrations of an odor what is the sensation? high concentrations?
smell sensation is unspecific; specific
What are the 6 primary smells?
floral, fruit, spicy, resin, burnt, and putrid
Olfactory receptors are what in the neural pathway?
primary afferent neuron; both the transducer and encoder of the signal
Chemosensory transduction takes place where?
mucus lining the surface
What are the characteristics of the olfactory receptor?
short peripheral process extends to surface of mucosa, long central process runs from nasal cavity to olfactory bulb (unmyelinated axons slow AP), turnover every 4-8 weeks
What is the role of the supporting cells?
produce mucus; flows constantly replaced every 10 minutes.
What is the role of mucus in smell?
Odorants dissolve in mucus b4 receptor, water base with dissolved salts, mucopolysaccharides and odorant-binding proteins.
odorant-binding proteins contribute to what?
odorant concentration or removal
