Fox, part of Chapter 10, figure from chapter 8
There are 5 "special" senses
touch (somesthesis) - already covered in previous outline
taste (gustation) - next (this outline)
smell (olfaction - after taste (this outline)
hearing (audition) - a big topic, next outline
sight (vision) - a huge topic, the outline after next
for chemicals dissolved in water
Gustation - chemicals - Many "flavors" are smell
Hanig (1901) - preferential localization:
sweet - tip of tongue
salt - front sides of tongue
sour - back sides of tongue
bitter - back middle of tongue
Papillae: Circumvallate (preference for quinine), foliate, fungiform (preference
also receptors in epiglottis
epiglottis via nerve X (vagus), circumvallate (9 of them) via IX (glossopharyngial),
others via VII (facial)
Several types of papilla including the circumvallate papillae on the back
of the tongue, shown in this picture
from our histology course
Within each papilla are numerous clusters of cells called taste
buds shown in this histology picture. support cells and sensory cells
Note that there are taste "blindnesses" Ptc = phenylthiocarbamide,
taster is dominant and nontaster
Use taste vs. non-taste to screen for G-protein coupled receptors (M. Barinaga,
Family of bitter taste receptors found, Science 287, 2133-2135, 2000)
generally, channel or G-protein linked receptor ultimately increasing calcium
somehow for synapse
note receptor does not have axon
salt - Na+ channel opens (depolarization)
sour - pH sensitive channel closes (depolarization)
sweet - G-protein linked cAMP close K+ channel - depolarize
bitter -G-protein cascade
umami (glutamate) - and amino acids, channels as well as G-protein cascade
In each case, Ca2+ involved in vesicle release
(much simpler than for olfaction)
Gustatory nucleus in medulla,
there to thalamus and then to sensory cortex, overlap to touch area - postcentral
also from medulla to hypothalamus
There are unusual primaries like aromatic and putrid , there may be many
primaries, although mixtures give a single perception confounding the ability
to define primaries
Relative to other senss, receptors difficult to stimulate
Even more than with the sense of touch, olfaction is related to motivational
The sense of smell is especially important in other animals (dogs)
Anatomy of olfactory epithelium.
Note: the receptors are neurons with axons, unlike for taste
Receptors are ciliary, with cilia in mucus
Transduction - G protein coupled receptor via adenylyl cyclase
There is a specialized olfactory alpha subunit of the G protein (Golf)
Na+ - Ca2+ channel is like that of photoreceptor in that cAMP acts as a
ligand to open the channel from inside the cell
Ca2+ opens Cl- channel
there is also a pathway involving PLC and IP3, but which is otherwise similar
in the background, there is a Na+/Ca++ exchanger
G-protein coupled receptor is very variable (there may be thousands, meaning
that olfactory receptors contribute predominantly to diversity of G-protein-coupled
receptors) and has specific variable regions
Axel and Buck won the 2004 Nobel
prize (Physiology and medicine for this contribution)
Glomeruli - > Mitral cells -> lateral olfactory tract
Olfaction is a complex sensory system in part because of the CNS projection
to amygdala, hypothalamus, hippocampus) , areas called Limbic system
There are senses outside the 5 special senses
note proximity with cochlea (for hearing)
utricle and sacculus linear motions
3 semicircular canals - rotations
stones (otoconia) provide mass for bending in utricle and sacculus
cupula displaced as semicircular canal fluid is displaced
TRANSPARENCY Fig. 10.14
hair cells (also for audition) [mechanoreceptor]
kinocilium (real cilium)
plus about 30 stereoocilia
mechanoreception assisted by tip links - depolarization if move toward kinocilium
hyperpolarize if in opposite direction
Test questions from 2004 - 2011 relating to this outline
Name (or give the number for) one of nerves that connect the taste receptors
to the brain.
vagus 10, glossopharyngial 9, mostly facial 7
A gustatory receptor sensitive to quinine has a G protein-coupled receptor;
the cascade results in calcium ions being released from an endoplasmic reticulum.
Why would an increase in cytoplasmic calcium ions be useful in gustatory
for release of synaptic transmitter vesicles
Monosodium glutamate affects which taste receptor primary?
The diagram of axons from olfactory receptors does not show connection to
the closest glomerulus. What characteristic of the olfactory receptor determines
which glomerulus it connects to?
ones that respond to the same primary pool to the same glomerulus
Approximately how many G protein coupled receptors are there for human olfaction?
Gustatory receptors connect to cranial nerves that project to the brain.
Name one of the three places in this projection pathway.
medulla, thalamus, postcentral gyrus
What is the cause of the difference among the students in the physiology
class as to whether they could taste PTC?
genetic, non-tasters are homozygous recessive
When a G protein coupled cascade in an olfactory receptor alters the cAMP
level, what does this cAMP do?
gates a channel
Say something about what "hair" means with respect to hair cells
in the vestibular or auditory systems.
real cilium=kinociliun and cilia-like stereocilia
Some taste cells depolarize in response to the appropriate chemical stimulation.
What must happen, downstream of depolarization, for vesicles of neurotransmitter
to be released?
Calcium ions must come in through calcium channels
Contrast how cAMP gates a cation channel in an olfactory receptor cell with
the way acetylcholine gates the nicotinic receptor.
cAMP from inside the cell, Ach from outside, both channels are ligand gated
The receptor molecule for gustation is either (what?) or (what?).
a channel or a G protein coupled receptor
The chemoreceptive part of the olfactory cell is in the nasal cavity. Where
is the synapse?
In the olfactory bulb (first cranial nerve) of the brain
In the vestibular system there are 3 fluid-filled (what) plus 2 organs with
otoliths, the (what?) and the (what?). [Answer one of the above.]
semicircular canals, utricle & saccule
What type of molecule must come in many varieties to mediate the richness
of olfaction you enjoy?
G protein linked receptor
Where is the first synapse in the olfactory system?
What is detected when endolymph bends the cupula?
What does the term "umami" refer to?
a taste, glutamate
Which sensory system projects to the limbic system, including the amygdala?
After a bitter tastant causes Ca2+ to increase in the cell, what does that
cause transmitter release
Out of the 5 special senses, which one does not have a localized area of
the cerebral cortex as its final projection?
About how many different G protein coupled receptors are involved in human
In addition to the vestibular sense, which utilizes hair cells where "hair"
refers to stereocilia?
All taste cell types, by one mechanism or another, have an influx of Ca2+.
What process does this increased cytoplasmic calcium mediate?
synaptic vesicle release
A portion of the brain hypothesized to be involved in olfaction, emotion,
limbic system (or any part of it)
What is PTC (phenylthiocarbamide) and what did it reveal about sensory transduction?
a substance that tastes bitter and helped in the isolation of the G protein-coupled
How is the richness of olfactory experience coded in the genes for olfactory
a different gene for each G protein-coupled receptor, very variable
Upon stimulation, for each taste primary, cytoplasmic Ca2+ increases. What
is it used for?
for release of transmitter vesicles
The ciliary receptor cells in the nasal epithelium have axons that terminate
olfactory bulb (first cranial "nerve")
What brain center involved in motivational aspects of hunger does the olfactory
bulb project to?
There are three nerves that carry taste information to the brain. These
three nerves are among a famous set of about a dozen that are collectively
referred to as (what)?
In olfactory transduction, what does cAMP do to affect the electrical properties
of the receptor cell membrane?
cAMP is the ligand that gates the cation channel from inside the cell
Where are the sense organs that monitor your head position to keep your
eyes upright for slight tilting of the head?
near the cochlea (for hearing)
In what way does the tastant for umami relate to a central nervous system
About how many olfactory receptor molecules does a human have?
In addition to G protein-coupled receptors, what is the other type of taste
In taste receptors, Ca2+, mediating transmitter release, comes from either
outside the cell or (what subcellular structure?)?
Where do olfactory neurons make their synapses?
What are the "hairs" of hair cells, and what happens when they
cilia (stereocilia), open or close channel, depolarize or hyperpolarize
In what way are calcium ions essential for the signaling of the taste receptor
cells to the cranial nerves?
mediate exocytosis of vesicles
In some cases, taste receptor molecules are channels. Alternatively they
G protein coupled receptors
Why do olfactory axons seem to zig-zag rather than just connect to the closest
glomerulus? (That pertained to yellow and green receptors, as colorized
in your figure, connecting to yellow and green glomeruli.)
presumably, each glomerulus receives only from receptors expressing the
In the G protein-coupled receptor cascade in the olfactory cell, how did
the cAMP affect the cell's response?
ligand close K+ channel
Describe the receptor cells of the vestibular system with respect to their
(1) structure, or (2) the type of stimulus that excites them.
(1) "hair" cells with stereocilia, mechanical
On the back of the tongue, taste buds are found on what larger structure
(hint, nine of them, and the nerve projects by the IX cranial nerve, the
65. In terms of the respective molecular biology of transduction, why is
olfaction a much richer sense than taste in humans?
There are maybe a thousand receptors for different primaries
Where is the first synapse in the sense of taste?
in the taste receptor cell
In olfactory transduction, what does cAMP do?
ligand for channel
By looking in the genome at G protein coupled receptors, what was isolated
when responders vs. nonresponders to PTC (phenylthiocarbamide) were
bitter taste receptor
For the fifth taste primary (other than sweet, sour, salt and bitter), what
chemical(s) stimulate it?
glutamate, amino acids
Where is the first synapse in the sense of smell?
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