ENGN/BIOL 267
http://www.youtube.com/watch?v=BPDu0T
vUtAU
http://dsc.discovery.com/videos/perfectpredators-shorts-white-tip-blind-killer.html
http://www.youtube.com/watch?v=5JWvTF
ZZsAc







Visual
Odors
Mechanical
Thermal
Salinity
Oxygen/Carbon Dioxide concentration
Electrical
But how do we really know electrical signal
helps sharks find their next meal???
sand
Plaice (weakly electric fish)
Fish
odors
sand
Fish
odors
sand
Polyethylene film coated box:
An “electric shield”
sand



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)
To epidermis/ocean water
Ampullary canal: filled with
Mucous-like, sugary gel
Ampulla:
Bulblike termination of canal
Alveoli: individual “pouches”
Bv = blood vessel
Mn = myelinated nerve
Receptor Cells line bottom of ampulla.
Electrical stimulus Neural signal
From Waltman Acta Physiol. Scand. (1966) “The Fine Structure of Ampullary Canals of Lorenzini”
LAMINAR SECTION
THROUGH CANAL WALL
SAME, ZOOMED IN
100 um
Epithelial Cells form tight junctions
SECTION THROUGH AMPULLARY
ALVEOLUS
RECEPTOR CELL FORMS SYNAPSE
Accessory cell: electrical
insulation for receptor cells
Receptor Cell
Presynaptic ribbon:
Connection coming from
receptor cell  nerve terminal
Nerve terminal:
Path to sensory neuron
Synapse formation
Subthreshold
response
Action
potential
A cartoon model of the
receptor cell making synapse
onto nerve.
* Receptor cells are electrically active!
• Exhibit all-or-nothing response
From Obara and Bennett: J Physiol (1972) “Mode of Operation of Ampullae of Lorenzini Skate, Raja
Icanal
Nrc ~20000
Iapex ~ Icanal
20 kW
1.2 MW
12 kW
Voltage drop across apical membrane is about 97.4% of Vin  Only 2.6% loss of signal strength!!