Unit 2 Week 1 Flashcards
What are examples of sensory stimuli?
chemical senses
auditory system
somatic sensory system
visions part I and II
What are the two examples of chemical senses?
taste (gustation)
smell (olfaction)
What impacts our perception of flavor?
chemical senses
-taste and smell
other sensory modalities
-temp
-texture
What are we actually tasting?
hydrophilic chemicals that dissolve in saliva
What is taste for?
-distinguish between food and poison
-distinguish between different types of food
-important for the control of feeding
What are the 5 basic tastes? Include examples of chemicals that cause the taste
Saltiness - NaCl
Sourness - H+
Sweetness - Sucrose
Bitterness - Caffeine
Umami - Glutamate
Define Tastant
a chemical that stimulates the sense of taste
Describe the anatomy of the tongue
covered in papillae, each papillae has about 100 taste buds
taste buds have synapses, taste receptor cells,
What are taste receptor cells?
respond the taste stimuli, 50-150 TRCs per taste bud
Where does the synapse from a taste bud go?
onto gustatory afferent axons, pass along taste sensing
Describe the central taste pathway
- taste receptor cell
- gustatory nucleus
- VPM of thalamus
- gustatory cortex
Describe receptor potential
-a stimulus-induced change in the membrane potential of a sensory receptor
-can be depolarizing or hyperpolarizing
What is unique about taste receptor cells?
can respond to more than one basic taste, but with preference
When the taste receptors depolarize and release transmitters, what is the result?
excitatory effects on downstream neurons
Describe sensory transduction
the process by which an environmental stimulus causes an electrical response (receptor potential) in a sensory receptor cell
How is sensory transduction possible?
ion channels, GPCRs
What are the mechanisms of taste transduction?
During the transduction process, taste stimuli may:
-pass directly through ion channels
-bind to and block ion channels
-bind to G-protein-coupled receptors (GPCRs) and activate a second messenger to open ion channels
Which taste types use Ion Channels as receptors vs. dimer GPCRs?
Saltiness and Sourness - Ion Channels
Sweetness, Bitterness, and Umami - GPCRs
Describe the detection of saltiness
Salt-sensitive taste cells
-activate special Na+ selective channel
-cause depolarization
-release serotonin to activate gustatory afferent axons
Describe the detection of sourness
Proton-sensitive tase cells
-activate H+- selective channel
-block K+ - selective channel
-cause depolarization
-release serotonin to activate gustatory afferent axons
What are the two ways to detect sourness?
Both H+ channel and K+ channel
What are the receptors for bitter, sweet, and umami?
bitter : T2Rs (25 types)
sweet: T1R2 + T1R3
umami: T1R1 + T1R3
Describe the detection of bitterness, sweetness, and umami.
Transduction process:
-activate GPCRs
-trigger the PLC to IP3 to Ca2+ signaling cascade
-cause depolarization
-release ATP to activate gustatory afferent axons
Define receptor potential:
a) an action potential in a sensory axon
b) hyperpolarization of the receptor membrane
c) the potential for a receptor to fire
d) a change in membrane potential in a receptor in response to an appropriate sensory stimulus
D
Which of the following is not a basic taste?
a) bitter
b) sweet
c) spicy
d) umami
C
For sensing sweet and umami, which of the following is TRUE?
a) there is a different ligand-gated channel to sense each
b) the transmitter released in response to these is different
c) both use dimers of G-protein coupled receptors
d) the second -messenger pathways used are different
C
Describe the function of smell
Smell: detection of airborne chemicals
-warns of harmful substances/danger
-combines with taste for identifying foods
-serve as a most of communication
Described the simplified central olfactory pathway
- olfactory receptor cells
- glomeruli
- 2nd order olfactory neuron
- olfactory cortex
Describe the relationship between olfactory receptor neurons (ORNs) and odorants
ORNs are activated by odorants
What is an odorant?
a chemical that stimulates the sense of smell
What is unusual about intracellular Cl- levels in dendrites of olfactory cells?
higher intracellular Cl- allows Cl- to leave cell visa Ca2+ activated Cl- channels leading to depolarization
Describe the mechanism of olfactory transduction
-odorants bind to GPCRs
-activate G-protein and adenylyl cyclase
-increase cAMP level
-open cAMP-gated cation channel (Na+ and Ca2+ influx)
-open Ca2+ activated Cl- channel (Cl- flow out of the cell)
-become depolarized and fire action potential
Describe the specifics of ORN expression and activation.
-each ORN expresses a single odorant receptor
-each ORN can be activated by multiple odorants
Each ORN expresses only one receptor, but that one receptor can detect multiple scents
How are odorants represented?
By multiple combinatorial activation of ORNs
Describe the makeup of an olfactory bulb
~2000 glomeruli
-each glomerulus receives inputs from one type of ORN expressing the same receptor
-creates a sensory map
What is a sensory map?
an orderly arrangement of neurons that correlated with certain features of the environment
What are two examples of spatial representations of olfactory information at the olfactory bulb?
-olfactory population coding
-olfactory maps
What are GCaMPs?
a class of genetically encoded Ca2+ indicators used in calcium imaging
What is calcium imaging used for?
visualizing neuron activity with in vivo
What is temporal coding in the olfactory system?
the representation of information by the timing of action potentials rather than by their average rate
For olfactory receptors in vertebrates, which of the following is part of the response to an odorant?
a) an odorant directly activates an ion channel
b) cAMP levels increase
c) a chloride channel opens and this makes the cell more negative
d) cAMP-gated ion channel is closed
What is a sensory map?
a) temporal patterns of spiking that produce different sensations
b) a set of population-coded information specifying properties of stimulus
c) a spatial representation of the timing of action potentials
d) orderly arrangement of neurons correlated with certain features of the environment
D
What is true of population coding?
a) a large number of neurons specify the properties of a stimulus
b) there is an orderly spatial arrangement of neurons
c) olfactory receptor cells are each responsive to only a single odor
d) none of the above
A
What are sounds?
sounds are audible variations in the air pressure (sound waves)
What is the audible range for humans?
20Hz - 20,000 Hz
What is the relationship between pitch and frequency?
high pitch = high frequency
low pitch = low frequency
What is the relationship between amplitude and intensity?
low intensity, low amplitude, quieter
high intensity, high amplitude, louder
What is the sensation organ for sound detection?
cochlea
Where are sounds converted into membrane vibration?
tympanic membrane (eardrum)
What are the first stages of the auditory pathway?
- sound wave
- tympanic membrane
- ossciles
- oval window
- fluid in cochlea
- auditory sensory neuron
What happens in the middle ear?
-sound force amplification by the ossicles (function like levers)
-much greater pressure at oval window than eardrum so that footplate can move fluids in cochlea, in response to sounds
What are the three ossicles?
malleus, incus, stapes
What happens in the inner ear?
transduction of sound energy into neural signals
What is the organ or Corti for?
contains auditory receptor cells (hair cells)
How many chambers are there in the inner ear? What fluids fill them?
3; two of them are filled with perilymph and one is filled with endolymph
Describe the contents of perilymph vs. endolymph
perilymph: a liquid with 7 mM K+ and 140 mM Na+
endolymph: a liquid with 150 mM K+ and 1mM Na+
How do vibrations travel?
in cochlear fluid
What does the vibration of cochlear fluid lead to?
the vibration of the basilar membrane
What are hair cells? Where can they be found?
hair cells are the auditory sensory cells that are activated by sounds
they sit on the basilar membrane in the organ of Corti
Why type of cells are hair cells? How do they work?
mechanosensory
1. sounds
2. sterocilia
3. receptor potential in hair cells
What controls the receptor potential of hair cells?
depends on the bending of stereocilia
increased tension = higher receptor potential
Describe transduction by hair cells
- stereocilia bends and tip link is stretched
- mechanically-gated K+ channel open and K+ ion enters the cell
- hair cells depolarize
- calcium influx through VGCC
- release the transmitter glutamate
What are the auditory sensory cells?
hair cells
How do hair cells get their name?
have stereocilia (hair-like structure) in the apical surface
What are the two types of hair cells?
OHC - outer hair cells
IHC - inner hair cells
Describe IHC
dominate synaptic output to spiral ganglion cells (SGCs)
1 IHC feeds ~ 10 SGCs
IHC contribute to 95% output to SGCs
What is the ration of OHC/IHC?
3:1
Describe OHCs
amplify basilar membrane deflections
depolarized
motor proteins are compressed
hair cells are shortened
function as the cochlear amplifier
What is the cochlear amplifier?
loop mechanism that causes the stereocilia of IHC to bend more
Describe what happens during human deafness
-hair cell damage or lost is the most common cause
-in many cases, auditory nerves remain intact
-can require a cochlear implant: an artificial, electrical cochlear
Which of the following contains auditory receptor neurons?
a) tectorial membrane
b) basilar membrane
c) organ of corti
d) none of the above
C
What are the two properties of sound?
frequency (pitch)
intensity (loudness)
What is a characteristic frequency?
a given intensity frequency at which a neuron is most responsive
auditory nerve responses are frequency tuned
Describe the properties of the basilar membrane of the cochlea along its length
Base: stiffer and narrower
Apex: more flexible and wider
What is the tonotopy of the basilar membrane of the cochlea?
high frequency at the base, low frequency at the apex
Define Tonotopy
the systematic organization within an auditory structure based on the sound frequency
as sensory map for the auditory system
What is phase locking?
the consistent firing of a neuron at the same phase of a sound wave
important for encoding low frequency sound
When does phase locking occur?
low-frequency sound can elicit phase-locked response in auditory neurons
phase locking occurs with sound waves up to ~5 kHz
It happens on every cycle or some fraction of cycles
Can high-frequency sound elicit phase-locked response?
no
Describe the mechanisms that can be used for encoding sounds for the following frequencies:
20-200 Hz
200-5,000 Hz
5,000 Hz - 20,000 Hz
phase locking
tonotopy + phase locking
tonotopy alone
What impacts encoding sound intensity?
-firing rate of auditory nerve
-number of active neurons in auditory nerve
How do we localize sound in the horizontal plane?
-required a comparison of the sounds reaching the two rears
-Interaural Time Delay (ITD)
-Interaural Intensity Difference
-Depend on sound frequency
What is the Interaural Time Delay (ITD)?
difference in time for sound to reach each ear
sound reaches the closest ear first
works with a frequency range of 20-2,000 Hz
What is the Ineraural Intensity Difference (IID)?
sound at one ear less intense because of head’s sound shadow
sound intensity is larger at the closest ear
works for sounds with a frequency range of 2,000Hz- 20,000Hz
What is sensitive to ITD?
superior olive, has binaural neurons
-receives inputs from both left and right cochlear nuclei
-selective for interaural time delay
What is the Duplex theory of sound localization in the horizontal plane?
ITD: 20-2,000 Hz
IID: 2,000 - 20,000 Hz
How do we localize sound in the vertical plane?
-vertical sound localization based on reflections from pinna
-the delays between direct path and the reflected path changes as the sound source move vertically
Which of the following is a definition of phase locking?
A. the firing of a neuron at 60 Hz
B. firing of a cell at the same phase as that of a sound wave
C. Firing of the cell at a predetermined frequency that is independent of the sound wave
D. the locking of the neuron’s firing rate to that of the body’s circadian rythym
B
