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Transcript
10/25/16
Some updates to original. I will
probably update more later
Five sensory modalities recognized since ancient
times
•
•
•
•
•
Vision
Hearing
Touch
Taste
Smell
Ideal Sensory Receptor
Response
Stimulus
•Rapid response
•Large amplitude
•Rapid recovery
•Steady baseline
Important Features for Sensory Receptor Cell
Function
• High Sensitivity
• Adaptation
• Receptors code relative stimulus, not
absolute size
advantages of ionotropic vs
metabotropic signaling
“Ionotropic versus Metabotropic”
Sensory Receptors
Fast
Amplification
Response
Stimulus
A
A*
B
A
A*
B*
Notice anything strange given what he just said
about an ideal receptor?
C
C*
Which fire action potentials
•
•
•
•
•
Photoreceptors
Olfactory receptor neurons
Inner hair cells
Outer hair cells
Pain sensing neurons in your arm
Which fire action potentials
•
•
•
•
•
Photoreceptors
Olfactory receptor neurons
Inner hair cells
Outer hair cells
Pain sensing neurons in your arm
Signaling is metabotropic in which of
the following
• Photoreceptors
• Olfactory receptor neurons
• Hair Cells
Signaling is metabotropic in which of
the following
• Photoreceptors
• Olfactory receptor neurons
• Hair Cells
Ions responsible for depolarization
• Hair cells
• Olfactory receptor neurons
• Photoreceptors
Ions responsible for depolarization
• Hair cells
Mostly K, also Ca
• Olfactory receptor neurons
Na, Ca, Cl
• Photoreceptors
Na,Ca
Does the base of the basilar
membrane respond to high or low
frequencies?
Width greater at base or apex?
More stiff at base or apex?
Does the base of the basilar
membrane respond to high or low
frequencies?
High
Width greater at base or apex?
apex
More stiff at base or apex?
base
Cochlea Sound Frequency Tuning
Know that this is called
tonotopic mapping
Does deflection of stereocilia towards
the kinocilium depolarize or
hyperpolarize hair cells? What
experiment was done to show this?
Deflection of Hair Cell Bundle Towards
Kinocilium Causes Depolarization
Towards the kinocilium is moving in the direction where
the little hairs get taller.
Describe two experiments you could
do to find the preferred frequency
(characteristic frequency) of a hair cell
Hair Cells Frequency Tuning
can you explain the oscillation stuff in
hair cells with channels and stuff
Voltage- and Calcium-Activated Channels Shape
Hair Cell Voltage Responses
Tuning Frequency and K+ Conductance
Inner vs outer hair cells
sorry these are poorly phrased, but hopefully
you get the point
• Which type of hair cell is primarily responsible for
hearing
• Which type of hair cell is primarily responsible for
tuning
• Which type of hair cell provides most afferent input to
the brain
• Which type of hair cell receives efferent input from the
brain
Inner vs outer hair cells
sorry these are poorly phrased, but hopefully
you get the point
• Which type of hair cell is primarily responsible for hearing
– Inner. These are the hair cells that actually carry sound information.
• Which type of hair cell is primarily responsible for tuning
– Outer. Outer hair cells can change shape to damp movement of the
membrane, or amplify oscillations at certain frequencies.
• Which type of hair cell provides afferent input to the brain
– Inner. If you do not know what afferent means, google it. This should
make sense.
• Which type of hair cell receives more efferent input from the brain
– Outer. If you do not know what efferent means, google it. This should
make sense.
Channels responsible for the
depolarization of olfactory receptor
neurons are gated by
Channels responsible for the
depolarization of olfactory receptor
neurons are gated by
• Cyclic nucleotides (cAMP)
• There are also Ca activated chloride channels.
Signal Transduction in Olfactory Neurons
How would depletion of extracellular
Na+ influence the olfactory receptor
neuron response?
How would depletion of extracellular
Na+ influence the olfactory receptor
neuron response?
• The response would be reduced, but the cell
would still respond because you would still get
calcium influx and activation of Ca gated
chloride channels which depolarize ORNs
Signal Transduction in Olfactory Neurons
Signal Transduction in Olfactory Neurons
SITS is a chloride
channel blocker
Which ion is important for adaptation
in olfactory receptor neurons
Which ion is important for adaptation
in olfactory receptor neurons
• Calcium. Always calcium
Adaptation of the Olfactory Neurons
Why do
you think
they
normalized
the
responses?
Where are the receptors located
Signal Transduction in Olfactory Neurons
Here
Not here
Taste
Taste transduction
Vertebrate photoreceptors release
•
•
•
•
Glutamate
GABA
Glycine
Depends on whether they are part of the ON
or OFF pathway
Vertebrate photoreceptors release
•
•
•
•
Glutamate
GABA
Glycine
Depends on whether they are part of the ON
or OFF pathway
Channels responsible for the
depolarization of photoreceptors in
vertebrates are gated by
Channels responsible for the
depolarization of photoreceptors in
vertebrates are gated by
• Cyclic nucleotides (cGMP)
– Remember that in ORNs it was cAMP
Cyclic GMP-Gated Channels
The vertebrate photoresponse can be
described as a
•
•
•
•
Conductance increase EPSP
Conductance decrease EPSP
Conductance increase IPSP
Conductance decrease IPSP
• None of these. Why are you calling it a post
synaptic potential if we aren’t talking about
synaptic transmission
– Sorry. That’s true but the important stuff I am trying
to point out is still the same
The vertebrate photoresponse can be
described as a
•
•
•
•
Conductance increase EPSP
Conductance decrease EPSP
Conductance increase IPSP
Conductance decrease IPSP
– Photoreceptors have a constant inward current in the dark. When they
are activated by light, these channels close and photoreceptors
hyperpolarize.
Notice that the
photoresponse is reduction
of an inward current
Inward current
at rest
Reduction of inward current
light
Dark Current is Suppressed by Light
• If you were given
–
–
–
–
–
Rhodopsin
Transducin
PDE
cGMP/GMP
CNG channel
could you give a brief outline of the rod
photoresponse
Baylor 1996
• Rods can respond to a single photon of light.
Which steps in the previous thing are sites of
amplification
Calcium and Photoreceptor Adaptation
Baylor 1996
Losing which would be most damaging
for your ability to see a wide range of
wavelengths
• S-Cones
• M-Cones
• L-Cones
Losing which would be most damaging
for your ability to see a wide range of
wavelengths
• S-Cones
Less overlap
with other
types of
photoreceptors
Photoreceptor Spectral Tuning
In humans there are two blind spots
for rod vision. What/where are they?
In humans there are two blind spots
for rod vision. What/where are they?
• Optic disk – where RGC axons exit the retina
• Fovea – There are only cones in the fovea
Rod Cone Distribution in Human Retina
Cross section through human fovea
What are some differences between
rods and cones
Rod and Cone Photoreceptors
Rods:
A. High Sensitivity
B. Slow Response
C. Monochromatic
Cone Opsin
Cones:
A. Low Sensitivity
B. Faster Responses
C. Color Vision
Be careful with the ones in boxes. If he asks a test
question about differences in phototransduction
between rods and cones, C is not an answer. Color
vision comes from having multiple cones that
preferentially respond to different wavelengths.
Photocurrent (pA)
Comparison of Rod and Cone Physiology
CONE
ROD
0
0
-5
-20
-10
-40
-15
0
4
8
12
0
4
t (s)
8
12
t (s)
ROD
CONE
Normalized Response
1.0
0.5
0.0
1
10
2
10
3
10
PIGM* / cell
4
10
5
10
Which ion is important for adaptation
in photoreceptors
Which ion is important for adaptation
in photoreceptors
• It is always calcium
– We will talk about why/how next week
Calcium and Photoreceptor Adaptation
Baylor 1996
Photoreceptor Responses to Light
Light Adaptation Reduces Cone Sensitivity
Dark
1.0
8.8 X 103
0.8
R/Rmax
4.0 X 104
0.6
0.4
0.2
0.0
1
2
3
4
Log Light Intensity
5
6