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ENGN/BIOL 267. vUtAU predators-shorts-white-tip-blind-killer.html

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Presentation on theme: "ENGN/BIOL 267. vUtAU predators-shorts-white-tip-blind-killer.html"— Presentation transcript:

1 ENGN/BIOL 267

2 vUtAU predators-shorts-white-tip-blind-killer.html ZZsAc

3  Visual  Odors  Mechanical  Thermal  Salinity  Oxygen/Carbon Dioxide concentration  Electrical But how do we really know electrical signal helps sharks find their next meal???

4 Plaice (weakly electric fish) sand

5 Fish odors

6 sand Fish odors

7 sand Polyethylene film coated box: An “electric shield”

8  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.”

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12  “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!

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14 Injected ink shows distribution of sensory canals. From Montgomery et al. Journal of Experimental Biology 202, 1349–1355 (1999)

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16 Ampulla: Bulblike termination of canal Alveoli: individual “pouches” Bv = blood vessel Mn = myelinated nerve From Waltman Acta Physiol. Scand. (1966) “The Fine Structure of Ampullary Canals of Lorenzini” Ampullary canal : filled with Mucous-like, sugary gel Receptor Cells line bottom of ampulla. Electrical stimulus  Neural signal To epidermis/ocean water

17 LAMINAR SECTION THROUGH CANAL WALL SAME, ZOOMED IN Epithelial Cells form tight junctions 100 um

18 SECTION 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

19 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

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22 N rc ~20000 I canal I apex ~ I canal

23 1.2 M  12 k  20 k  Voltage drop across apical membrane is about 97.4% of Vin  Only 2.6% loss of signal strength!!


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