Lecture 2-3: Matheson

Question 1

What types of electric sense are there?

Answer 1

Passive sense- detecting external fields

Active sense - detecting disruptions in the individuals electric field

Question 2

Describe passive electric sense?

Answer 2

Marine species e.g. sharks, skates, rays, catfish.
Can be animate bioelectricty or electrochemical
Used to detect external fields

Question 3

Describe active electric sense?

Answer 3

Detecting disruptions in the individuals electric field
Animate: conspecifics, predators, prey
Inanimate: anything in the envrionment with a different conductivity
E.g. all weakly electric fish

Question 4

What are the orders of weakly electric fish?

Answer 4

Gymnotiformes and Mormyriformes

Distantly related but evolved senses separately (convergent evolution)

Question 5

How are electrical discharges produced- what body part

Answer 5

Organs consiting of modified muscle cells (electrocytes which are stacked to produce electroplaques)
Surrounded by a insulating connective sheath
Produce electric organ discharge (EOD)

Tail muscles - weakly electric skates
Brachial muscles- strongly electric ray

Question 6

How are electrical discharges produced- mechanism

Answer 6

Channel of electroplaques formed with a current flowing through surrounding medium. Alternating +I- +I-

Current has to be forced out of the body into the environment

Timing of the electric pulses is controlled by the medulla

Question 7

What is the difference in the electric discharge in strongly and weakly electric fish

Answer 7

Strongly - monopolar discharge good for stunning
Weakly - bipolar or complex wave form (size and shape determined by innovation of the electroplaques)
-Gymotids –> wave shape (modified + varied sin wave)
-Mormyrid –> pulses (like action potentials)

Question 8

What are the properties of the electric organ discharge

Answer 8

Formation of an electric field around the organism

• One end positive the other negative
• Voltage decreases with distance, only active over a short range (formation of iso-voltage curves)
• Current flows at right angles to voltage curves
• Circuit generated and completed in the organism

Question 9

What are the two types of electroreceptive sense organs

Answer 9

All are hair cells and form part of the octavo-lateral sensory system (lateral line) which is used to detect vibrations.

Ampullary is one type of receptor - passive sense
- Jelly filled canal from inside through epidermis to outside
Tuberous receptors - active sense
- Low resistance plug between inside and outside
- Loosley attached to outside layers of epidermis
-Only found in electric fish.

Question 10

Describe ampullary electroreceptive sense organs?

Answer 10

Sensitive to weak electric field gradients allowing a behavioural response in response to low frequency signals.
Able to modulate responses as they are spontaneously active.
Fire tonically so can modulate in both directions
Can be used for navigation e.g. elasmobranchs

Question 11

Describe tuberous electroreceptive sense organs?

Answer 11

Respond to discharges of electric organs
Two types:
- Time markers + Amplitude coders
Allow for electro-communication and electro-location

Question 12

Why is the difference between time markers and amplitude coders?

Answer 12

Time markers- highly sensitive and fixed latency (phase locked), used to detect the fishes own EOD and also that of conspecifics
Amplitude coders: low overall sensitivity, but highly sensitive to changes in amplitude of the fishes own EOD

Question 13

How are tuberous electroreceptive sense organs used in mormyrids?

Answer 13

Time-coders: Knollenorgans (K receptors), 1-35 receptors cells but only 1 neuron, single action potential per EOD, electical synapses

Ampltidue coder: Mormyromasts (D receptors), two types (A&B) which are seperately innervated, respond with a burst of spikes with the latency of the first spike accounting for amplitude.

Question 14

How are tuberous electroreceptive sense organs used in gymnotids?

Answer 14

Pulse fish
-Time coders: M receptors, Amplitude coder: B (burst) receptor

Wave fish:
- T (time) receptors, P (probability) receptors

Question 15

What does electrolocation require?

Answer 15

Electric organ and tuberous electro-receptors

• Control of the EOD and sensory signals (pacemaker - in the medulla)
• Somatotopic map of the electro-sensitive body surface

Question 16

What is the purpose of electrolocation?

Answer 16

Detecting:
- location (allows for movement)
- Conductance, Capacitance, Distance
Allows them to visualise the environment even in murky conditions.

Question 17

How does electrolocation work?

Answer 17

Measuring disturbance in the environment
- no disturbance = no distortion
- Increased resistance (insulator) –> electric field diverted
- Increased conductance –> diversion to flow through hotspot, leading to less current flowing in other areas
The location of receptors which detect distortion indicate the objects location due to somatotopic map
If distortion is +/- indicates changes in conductance

Question 18

What electroreceptive sense organs do each type of fish use?

Answer 18

Morymyrids use mormyromasts

Gymnotids use all types

Question 19

How can electrolocation be used to detect distance?

Answer 19

More extreme changes in amplitude –> closer objects
- tested by placing electrodes at different distances
Image on somatotopic map:
- large and low contrast = far away
- small image in high contrast = close
Slope: amplitude ratio is proportional to distance

Question 20

What benefit is it to the electric fish being able to measure capacitance?

Answer 20

Capacitance is the store of electrical charge

• Organisms have high levels of capacitance, inanimate objects have low levels of capacitance
• Therefore allows the distinguishing of objects in environment.
• This is because it modifies the EOD

Question 21

How is the EOD modified by capacitance in Mormyrids?

Answer 21

Pulse type: modified shape but no changes in timing
Wave type: modified timing (frequency)
Mormyromasts detect waveform changes.
- A and B cells distinguish between resistance and capacitance

Question 22

How is the EOD modified by capacitance in Gymnotids?

Answer 22

T-type receptors detect timing changes, compare these to the rest of the body to detect and localise capacitive objects

Question 23

What are the two-key problems with electro-communication?

Answer 23

• How do you remain sensitive when producing your own EOD?

- How do you avoid interference with conspecifics? As the signals can also cancel out or summate

Question 24

How you get around the issue of sensitivity?

Answer 24

The knollenorgane is inhibited when the EOD occurs

This is controlled by the pacemaker

Question 25

How do you get around the issue of interference

Answer 25

Pulse type - spare signals
Wave type fish vary in frequency from 300-600 Hz with each individual having an individual frequency.

Must identify its frequency out of the groups- uses jamming avoidance response

Question 26

How does the Jamming avoidance response work?

Answer 26

• Detects which fish has the higher frequency, which one has a lower frequency, using sensory information and its electroreceptive organs.
• Monitoring frequency of own EOD and compares to conspecifics frequency. Extracts own frequency and then finds the difference.
• Shift in that direction to prevent jamming