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 Polyethylene film coated box: An “electric shield”
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.”
“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!
Injected ink shows distribution of sensory canals. From Montgomery et al. Journal of Experimental Biology 202, 1349–1355 (1999)
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
LAMINAR SECTION THROUGH CANAL WALL SAME, ZOOMED IN Epithelial Cells form tight junctions 100 um
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
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
N rc ~20000 I canal I apex ~ I canal
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!!