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!!