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-What ions tend to move through open nicotinic acetylcholine receptor channels?
-How does the function of the Na+-K+-2Cl- cotransporter in chloride cells of the Atlantic salmon likely change in saltwater vs. freshwater (you read about this in the Pelis et al. article for lab last week)?
-How does the membrane potential in rods and cones change (depolarize or hyperpolarize) in response to light?
- In general, how does transduction take place in vertebrate hair cells?
Other questions I thought about asking:
Draw a picture that illustrates a hypotonic cell (relative to the interstitial fluid surrounding it).Draw a graph of an action potential. Be sure to label the axes.Define transduction in the context of sensory reception. How do you calculate the emf (electromotive force) acting on an ion species?
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7-27 Randall et al. 2002
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10-24 Silverthorn 2001
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7-5 Randall et al. 2002
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Mechanisms and Molecules
Lots of Evolutionarily Conserved Elements
e.g., 7 transmembranehelices and G-proteinintermediate
e.g., Vision, olfaction, sweet and bitter taste(also muscarinic AChreceptors and many hormone receptors)
7-3 Randall et al. 2002
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Mechanisms and Molecules
Threshold of Detectione.g., 1 photon or hair cell movement of H diam.
Enzymatic Cascade to amplify
Sour (pH; H+) and salt (Na+) move directly – no amplification
To measure quality need many receptors grouped into organ; different ‘tunage’ (e.g, wavelength of light or frequency of sound)
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Enhancing Sensitivity
- Spontaneous basal activity
- Constant rate of APs
- Directionality if ↑ or ↓ AP frequency
7-12 Randall et al. 2002
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Tonic vs. Phasic receptors
5-19 Randall et al. 2002
Slow-adapting
fast-adapting
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-Accommodation
Randall et al. 2002
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Enhancing Sensitivity
- Efferent Control
e.g., stretch receptors in muscle control length so can perceive stretch
- Feedback Inhibition
Auto (helps keep in dynamic range)vs. Lateral…
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Enhancing Receptor Sensitivity
- Lateral Inhibition
e.g., improve touch sensitivity and visual acuity (edges especially)
7-14 Randall et al. 2002
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Vision
- light is focused by lens (and cornea) to create an image on the retina
- refraction by cornea (85%) and by lens (15%)
- alter focal length by altering shape and curvatureof lens
(zonular fibers and ciliary muscle ‘sphincter’)
- binocular convergence (both eyes on same part of retina)
LIGHT INTENSITY
- pupil for variable aperture via iris and radial muscle
FOCUS
7-34 Randall et al. 2002
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7-37 Randall et al. 2002
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10-27 Silverthorn 2001
1810-29 Silverthorn 2001
Out of focus
distant close
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Vision
- sclera white tough outer layer- choroid lots of blood vessels- pigment layer with photoreceptors- fovea where highest acuity and highest # cones
-(visual streak?)
- photoreceptors (rods and cones)-Transduce photons (light) into electrical signal
When light hits, the Na+ current into the cell is stopped and membrane hyperpolarizes stopping release of NT7-39 Randall et al. 2002
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Bleaching of retinal photoreceptors
Photoreceptors called cones respond to particular wavelengths oflight. Their response involves “bleaching” of their responsive pigment, so that for some seconds they are unable to respond again.
Expectation after 1
5
seconds?
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Bleaching of retinal photoreceptors
Photoreceptors called cones respond to particular wavelengths oflight. Their response involves “bleaching” of their responsive pigment, so that for some seconds they are unable to respond again.
Expectation after 1
5
seconds?
13
25
Bleaching of retinal photoreceptors
Photoreceptors called cones respond to particular wavelengths oflight. Their response involves “bleaching” of their responsive pigment, so that for some seconds they are unable to respond again.
Expectation after 1
5
seconds?
26
Rhodopsin mechanism: cis-trans isomerization of retinal molecule
Changes conformation of opsinmolecule and therefore initiates transduction
activa
ted
7-43 Randall et al. 2002
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Activated retinal changes conformation of opsin molecule (opsin and retinal separate) and initiates transduction