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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molt + iron filings

Mechanoreceptors: Hair Cells → Receptor Potentials

+ Deflection (µm)-1.0 +1.0

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Stretch SensitiveChannel (K+)

VCa+2

graded potential

NT release

Afferent Sensory Neuron

Deflection (µm)-1.0 +1.0

AP

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∝ 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