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Bioelectric Sensing in Sharks and Rays. ENGN/BIOL 267. Behavior and Electrosensory Capability. http://www.youtube.com/watch?v=BPDu0TvUtAU http://dsc.discovery.com/videos/perfect-predators-shorts-white-tip-blind-killer.html http://www.youtube.com/watch?v=5JWvTFZZsAc. - PowerPoint PPT Presentation
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BIOELECTRIC SENSING IN SHARKS AND RAYS
ENGN/BIOL 267
Behavior and Electrosensory Capability
http://www.youtube.com/watch?v=BPDu0TvUtAU
http://dsc.discovery.com/videos/perfect-predators-shorts-white-tip-blind-killer.html
http://www.youtube.com/watch?v=5JWvTFZZsAc
What sensory cues are important for predation?
Visual Odors Mechanical Thermal Salinity Oxygen/Carbon Dioxide concentration Electrical
But how do we really know electrical signal helps sharks find their next meal???
Plaice (weakly electric fish)sand
sand
Fish odors
sand
Fish odors
sand
Polyethylene film coated box:An “electric shield”
So far we know… Sharks don’t use visual sense to find
plaice Don’t use mechanical stimuli to find
plaice Suspect they use electrical sense, but not
yet proved. In Kalmijn’s words:
“However, such an indirect conclusion may indicate only a limitation on the human imaginative faculty if not tested thoroughly and affirmed by more direct evidence.”
The Big Question “How do they do it?
What about their physiology endows it with such keen electrical sensing?
How can we apply physics principles to understand/model the system?
And, equipped with this knowledge, what we be inspired to build?
Glad you asked...Good thing we’re all in bioE!
A bit of shark physiology
Pores leading to “jelly-filled canals” on the Ray (raja natusa) and tiger shark
Injected ink shows distribution of sensory canals. From Montgomery et al. Journal of Experimental Biology 202, 1349–1355 (1999)
Electroreceptors in the Shark
Ampullae of Lorenzini
Ampulla:Bulblike termination of canal
Alveoli: individual “pouches”
Bv = blood vesselMn = myelinated nerve
From Waltman Acta Physiol. Scand. (1966) “The Fine Structure of Ampullary Canals of Lorenzini”
Ampullary canal: filled withMucous-like, sugary gel
Receptor Cells line bottom of ampulla.Electrical stimulus Neural signal
To epidermis/ocean water
Ampullae of LorenziniLAMINAR SECTION THROUGH CANAL WALL SAME, ZOOMED IN
Epithelial Cells form tight junctions
100 um
Receptor Cell—Nerve TerminalSECTION THROUGH AMPULLARY ALVEOLUS
RECEPTOR CELL FORMS SYNAPSE
Nerve terminal:Path to sensory neuron
Presynaptic ribbon:Connection coming from receptor cell nerve terminal
Receptor Cell
Synapse formation
Accessory cell: electrical insulation for receptor cells
Coding electricity in neural impulses/responses
From Obara and Bennett: J Physiol (1972) “Mode of Operation of Ampullae of Lorenzini Skate, Raja
A cartoon model of the receptor cell making synapse onto nerve. * Receptor cells are electrically active!
• Exhibit all-or-nothing response
Subthreshold response
Action potential
Receptor cells at base of alveolus
Full circuit model
Current Divider
Nrc ~20000
Icanal
Iapex ~ Icanal
Equivalent Circuit
1.2 MW
12 kW
20 kW
Voltage drop across apical membrane is about 97.4% of Vin Only 2.6% loss of signal strength!!