Date post: | 16-Jan-2016 |
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Sensory Systems: Transducing the Environment~50 “senses”! (5 “modalities”)
1. Light (G-coupled photoreceptors)
2. Electromagnetic Fields (VG channels)
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• mostly visible (~380-760 nm)• opaque >near IR, <300 nm• damage at <300 nm• >IR (radio) very low energy
• generated by APs (muscle)• e-fields: sharks, fish, platypus• magnetic-fields: sea turtles, bees
• travels in straight lines=> determine direction & distance (paired detectors)
• fields lines = directional=> determine direction & shape
Sensory Systems: Transducing the Environment~50 “senses”!
3. Temperature (TRP channels)
4. Chemicals (G-coupled receptors)
• both ‘hot’ and ‘cold’ detection• most sensitive to T• surface & CNS (hypothalmus)
• taste = smell (water vs air) • highly specific (human = ~400 receptors)• high sensitivity
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• low directionality (convection) except some snakes w/ pits process as ‘visual’ information!
• low directionality (convection)
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5. Mechanical Deformation (stretch activation)
sound pressure gravity/acceleration
Cochlea
basilarmembrane
tectorialmembrane
Lateral Line Organ
Statocyst
Cupula
Hair Cellsstatolith
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Qu
ickTim
e™
an
d a
de
com
pre
sso
rare
nee
ded
to
see
th
is p
ictu
re.
molt + iron filings
Mechanoreceptors: Hair Cells → Receptor Potentials
+ Deflection (µm)-1.0 +1.0
Rec
epto
r P
ote
nti
al
Stretch SensitiveChannel (K+)
VCa+2
graded potential
NT release
Afferent Sensory Neuron
Deflection (µm)-1.0 +1.0
AP
Fre
qu
enc
y
∝ receptor potential
• “Stimulus” Intensity → AP Frequency
• Logarithmic Response → %Response %∝ Change
stereocilia
What about pitch (frequency)?
Different Signals Have Different Uses
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High Frequency Sound:• Scatters easily, penetrates poorly
• Paired Ears: Intensity, Phase & Timing
=> Useful for Directional & Spatial Info
Bat Sonar @ 100KHz = 3 mm wavelength QuickTime™ and aTIFF (Uncompressed) decompressor
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=> spatial resolution < 1 mm!
Low Frequency Sound:• Scatters poorly, penetrates easily
• Long WL = no for phase differences
• Elephants, whales, (birds?)
=> Long Distance Info
Ultrasound
Infrasound
Rangeof Human Hearing
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Signal Conditioning by Accessory Structures
Amplification:PinnaDrums, etc
w/o pinna
Tuning:Tectorial & BasilarMembranes
10KHz 1KHz 0.1KHz
decreasingstiffness
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Presynaptic Inhibition/Facilitation
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Fish Tail-Flip Response
axonal terminal = graded potential
⇓ Em ⇓ NT release
Sensory System?
Crossed InhibitoryInterneuron
InhibitorySynapse
1 NT/neuron