2. Sensory Systems: Transducing the Environment ~50 “senses”! (5 “modalities”) 1. Light (G-coupled photoreceptors) 2. Electromagnetic Fields (VG channels) 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

3. 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 low directionality (convection) except some snakes w/ pits process as ‘visual’ information! low directionality (convection)

4. 5. Mechanical Deformation (stretch activation) soundpressuregravity/acceleration Cochlea basilar membrane tectorial membrane Lateral Line Organ Statocyst Cupula Hair Cells statolith molt + iron filings

5. Mechanoreceptors: Hair Cells → Receptor Potentials + Deflection (µm) +1.0 Receptor Potential Stretch Sensitive Channel (K + ) V Ca +2 graded potential NT release Afferent Sensory Neuron Deflection (µm) +1.0 AP Frequency ∝ receptor potential “Stimulus” Intensity → AP Frequency Logarithmic Response → %Response ∝ %Change stereocilia What about pitch (frequency)?

6. Different Signals Have Different Uses High Frequency Sound: Scatters easily, penetrates poorly Paired Ears: Intensity, Phase & Timing => Useful for Directional & Spatial Info Bat Sonar @ 100KHz = 3 mm wavelength => 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 Range of Human Hearing

7. Signal Conditioning by Accessory Structures Amplification: Pinna Drums, etc w/o pinna Tuning: Tectorial & Basilar Membranes 10KHz1KHz0.1KHz decreasing stiffness

9. Presynaptic Inhibition/Facilitation Fish Tail-Flip Response axonal terminal = graded potential ⇓  Em ⇓ NT release Sensory System? Crossed Inhibitory Interneuron Inhibitory Synapse 1 NT/neuron