SHARK ELECTRIC SENSE

Electrical Circuit Model and Active Membranes

Shark goes coo-coo for E-fields!

http://www.youtube.com/watch?v=Prq2HK8cT3A&feature=player_embedded

Quick review: 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

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• “Negative-going spikes”

Bioelectricity: Active Membranes and Action Potentials

Action potential: fundamental unit of electrical communication

Synaptic Transmission

For sharks, think of this as the receptor cell’s presynaptic ribbon

And think of this as the nerve terminal that eventually reaches the brain

Step 1:Electrical Stimulus causes depolarization across membrane of receptor cells

Step 2:Voltage gated channels open, and Ca++ ions rush in.

Step 3:This triggers vesicle release. Electrochemical message sent to neuronbrain

Neural Signals: Spike Rates

Sensory Neuron

Receptor Cells SynapseOnto Sensory Neuron

No stimulus: temporally uncorrelated spiking behavior

Electrical Stimulus Causes Spike Rate to Increase in Frequency

Spike Rate Coding: Linear Relationship between Ampullary Stimulus and Neuron Spike Rate

Non-zero resting spike rate.

HH Zakon, 1988; Obara 1976

But wait: Nerve is spontaneously active!

Neural Signals: No stimulus

Sensory Neuron

Receptor Cells SynapseOnto Sensory Neuron

No stimulus: temporally uncorrelated spiking behavior

Neural Signals: Stimulus Present

Sensory Neuron

Receptor Cells SynapseOnto Sensory Neuron

With stimulus: Receptor cell activity synchronized. Causes neuron to fire action potential

References HH Zakon, 1988. Sensory biology of aquatic animals: electroreceptrs

diversity in structure and function

Waltmann, 1966. Electrical Properties of the Ampullary Canals of Lorenzini, Acta. Physiol. Scand. 66: 1-60.

J Bastian, 1994. Electrosensory Organisms Physics Today, Feb 1994: 30-37

RW Murray, 1962. The Response of Ampullae of Lorenzini of Elasmobranchs to Electrical Stimulation. J. Exp Biol, 39: 119-128

S Obara and MVL Bennett, 1972. “Mode of Operation of Ampullae of Lorenzini of the Skate, Raja. J. Gen. Physiol., 60: 534-557.

B Waltman, 1966. Electircal properties and fine structure of the ampullary canals of Lorenzini. Acta Physiol Scand Suppl 264:1