taste and smell

Question 1

Gustation

Answer 1

means to taste

Question 2

Five basic tastes

Answer 2

Saltiness (Na+)
Sourness (K+)
Sweetness (Sugars and some amino acids, ie: sucrose, fructose, aspartame)
Bitterness (K+, Mg+, quinine, caffeine, nicotine, and denatonium) -> survival
umami (glutamate and other proteins)

Question 3

the tongue

Answer 3

composed of papillae and taste buds

each papillae has one to several hundred taste buds

Question 4

taste receptor cells

Answer 4

non-neuronal by standard histology, but do form chemical synapses with gustatory afferent axons
life span of 2 weeks
has receptor potential
most taste cells respond to over two of the five tastants

Question 5

receptor potential

Answer 5

activation of cell by appropriate chemical

Question 6

Salty

Answer 6

Na+ influx
works down [] gradient
ions opened by Na+ ions

Question 7

sour

Answer 7

H+

inhibits the K+

Question 8

Bitter, sweet, and umami

Answer 8

they all work via g protein coupled receptors

Question 9

neural circuitry of taste

Answer 9

includes:
tongue, managed by nerves XII (hypoglossal), IX (glossopharyngeal), and vagus (X)
the medulla (NTS)
thalamus
gustatory cortex

Question 10

perception of flavor

Answer 10

mandated by volatile molecules going to olfactory nerves in nasal cavity
this process of smell is sped up via somatosensory stimulation of tongue and retronasal passage of odorants

Question 11

olfaction

Answer 11

the ability to discriminate scent
humans can detect >10,000 volatile chemicals, and highly trained perfumers can distinguish ~5,000 different types of odorants
wine tasters can distinguish >100 different components of taste

Question 12

olfactory system

Answer 12

lifespan 30-60 days, regeneration by basal stem cells
~5 cm^2 total for area
olfactory cells are embedded in specialized epithelium
the cells themselves are bipolar nerve cells, where the dendrite extends from apical end to epithelial surface, giving rise to thin cilia that protrude into the mucus of the nasal cavity
cilia recognize odorants that diffuse through mucus and transduce the smell into an electrical signal

Question 13

odorant receptor (G_off receptors)

Answer 13

phasic receptor with a mysterious underlying mechanism

odorants bind to the membrane of these receptors, which causes activation of adenylyl cyclase (makes ATP to cAMP by cleaving pyrophosphate)
cAMP then binds to specific cation channel which causes influx of Na+ AND Ca2+
the opening of Ca2+ activated chloride channels causes current flow and membrane depol

Question 14

Encoding of odorants

Answer 14

each olfactory sensory neurons expresses ONE odorant receptor
each receptor recognizes MANY odorants; each ODORANT can be recognized by multiple receptors
each odorant is detectable by a unique code of receptors and has a distinct pattern of signal to brain

Question 15

Olfactory bulb interneurons

Answer 15

has peri-glomerular cells and granule cells

the two provides better signal-to-noise ratio for odorant discrimination

Question 16

peri-glomerular cells

Answer 16

receives excitatory input from olfactory sensory neurons and have reciprocal synapses with the primary dendrites of mitral and tufted relay neurons suggesting a possible role in signal modification

Question 17

granule cells

Answer 17

reciprocal excitatory-inhibitory input with secondary dendrite of mitral and tufted relay neurons, provide negative feedback to relay neurons that shapes odor response

Question 18

Neural circuitry of olfaction

Answer 18

olfactory cell -> olfactory bulb -> olfactory tubercle -> thalamus -> orbitofrontal cortex
the olfactory bulb also sends information to olfactory cortex and related temporal lobe structures