1. Chapter 11: Electroreception 3/31/11
Lecture # 15
Chapter 11: Electroreception
3/31/11

2. Class survey on midterm
Developing individual questions
Helpful 1.8±1 Interesting 2 ±1
Developing group questions
Helpful 2.8±2 Interesting 2.9 ±2
Using questions to study
Helpful 1.7±1 Interesting 2.2 ±1.3
Questions on midterm
Good coverage 1.8 ±1.3 Time to study 3.2 ±2
My grade 2.4 ±1.1
Final study questions 28 Y
Class designed questions 24 Y

3. My suggestions
Final - only do individual questions and skip the group questions
Will be fewer questions on final and more time to prepare
Do chapter assignments now so you can think about these as you go through the chapters

4. Chapters 10 Chemical signals (2) 20 Signal honesty (1)
11 Electroreception (2) 21 Conflict resolution (2)
12 Optimizing comm (1) 22 Territorial signaling (2)
13 Amount of info (1) 23 Mating games (2)
14 Value of info (1) 24 Social integration (2)
15 Coding (1) 25 Environmental signal (2)
16 Signal evolution (1) 26 Autocommunication (2)
17 Costs and constraints (1)
18 Signal design rules (1)
19 Evolutionary game theory (1)

5. Final project Assignment is on class web page
For next time, give one sentence each:
What is your topic?
Why is it important?
Why is it interesting to you?
Based on this, I will try to find each of you a few references

6. Chemoreception - Ways of sampling
Taxis - orientation with respect to chemical gradient
Sampling
Simultaneous - uses two nostrils or receptors which are compared
Sequential - samples two nearby locations
Usually move head
Not as sensitive as simultaneous sampling so requires steeper gradient

7. Dog tracking scent
Wander back and forth across scent trail to find its edges
Then can figure out which way scent is increasing - getting closer to source

8. Snake tracking Female leaves a trail
Male samples trail with forked tongue
Touches vomeronasal organ on room of mouth
Follow females pheromones

9. Sampling in a current Concentration may be discontinuous
Use current flow to also guide upstream
If lose scent, fly across current till find plume
Gypsy moth
Star marks pheromone release site. Arrows show wind direction. Thick line show when in plume. Light line shows when out of plume - at that point flies perpendicular to current till finds plume again

10. Electroreception Sense which humans do not have
Only found in aquatic organisms
Fish
Amphibians
Mammals?
Book calls platypus a mammal. I think it is a monotreme

11. Forces Coulomb’s law gives force between two charged particles
Same form as gravitational force
 Is the permittivity constant

12. Fields Field is force felt by a unit charge
Tells you what a single charge would feel (and so would do) as it moves around in a space containing other charges
Measure in newtons / couloumb

13. Electrical potential
Work you would have to do to move a point charge from infinity to a particular location
Field is slope of potential
Measure potential in volts (Joules / coulomb)

14. Electric field around single charge - monopole
Symmetric
Force is stronger as move closer to charge
Charges would move along dashed lines
If charge same sign they repel and if opposite sign then attract
Solid lines like a contour map. Connect points of constant potential or constant field
Force increases with distance squared

15. Electric field around single charge - monopole
Symmetric
Force is stronger as move closer to charge
Charges would move along dashed lines
If charge same sign as center, repelled and if opposite sign then attracts +
Solid lines like a contour map. Connect points of constant potential or constant field
Force increases with distance squared

16. Electric field around dipole
Two charges, one + and the other -
Dashed lines show directions particle moves along + -

17. Physics simulations

18. Electric hockey

19. Generation of bioelectric fields
How can animals generate electric field?
Use electric potential across cell membrane

20. Ion pump creates a concentration gradient across cell membrane
Cl- K+
Na+ K+
Cl-
Na+
Na+ K+
Cl-
Na+ K+
Na+
Cl- K+
Na+
Cl- 3
Na/K ATPase
Cl-
Na+ K+ K+ 2
Na+ K+
Get concentration gradients
Also get charge gradient since 3 Na+ go out and 2 K+ go in. Net neg charge inside cell.
Cl-
Na+ K+
Cl-
Na+ K+
Na+
Cl- K+
Cl- K+ K+ K+
Cl-
Cl- K+
Outside cell
Inside cell

21. Also creates charge difference: Pumps 3 Na+ out and 2 K+ in-
141 mM
124 mM
3.3 mM
Na+
10-20 mM
5-10 mM mM
Cl-
Cl-
Na/K ATPase K+
Fain Fig 3.6 K+
Outside cell
Inside cell

22. Membrane potential
When channels are open, there will be a balance of diffusion and electrostatics
Concentration K+ K+
Charge -
Concentration gradient will make K+ diffuse out. But charge distribution (neg charge inside) will attract K+ to diffuse in. This will happen until the two forces are balanced.
This assumes K+ is only ion that can move through these channels
Mass and charge make K+ move in opposite directions

23. Walther Nernst Won Nobel prize in chemistry in 1920
Original “Nernst equation” was written for electrochemistry

24. Personification of Nernst equation - students in a classroom
Student metaphor - If there are 100 students inside a room and none outside, there would tend to be students going out the door. However if there were hot fudge sundaes inside the room, the students might tend to stay in or diffuse in rather than go out. The number of hot fudge sundaes necessary to keep the students in the room would depend on ratio of students in vs out. If only 10 hot fudge sundaes, then most of the students would go out. If 100 sundaes then more students would come in.

25. Students will move out until same density in and out

26. If there are a few hot fudge sundaes…
Might get few students coming back in

27. If there are lots of sundaes…
Hot fudge sundaes = membrane potential
Students = K+ ions
Everyone who wants one will come back in

28. Nernst equation
At equilibrium, can determine membrane potential which offsets concentration gradient across membrane K+ K+ + -
If the concentration outside is 1/10 that inside, it will take -59 mV inside the cell to compensate to reach equilibrium with this gradient
If concentration outside is 1/100 that inside, it will take -118 mV inside the cell
Nernst equation comes from Gibbs free energy and work
dG = w = qE = nFE but this is all at standard conditions Need to correct for actual concentration quotients
Ko - outside
Ki - inside Vm

29. Membrane potential increases till there is equilibrium
Na/K ATPase K+ - +
3.3 mM
141 mM
120 mM
15 mM
Na+
Na+
At equilibrium, K+ diffusing out is same as K+ diffusing in.
At this point the inside of the cell is negative
-60 to -80 mV
Outside cell
Inside cell

30. Excite neuron and channels open
Na/K ATPase K+ +
Na+
Na+
At equilibrium, K+ diffusing out is same as K+ diffusing in.
At this point the inside of the cell is negative
+50 mV
Outside cell
Inside cell

31. Electrocyte discharge
Electrocyte is innervated by neuron
When receives signal, cell depolarizes = change in voltage K+
Na+
-80 mV
Na+ K+
+50 mV

32. Excitable cells Discharge of single cell contributes -80mV to +50 mV
130mV change in potential
130 mV

33. Cell potentials add just like batteries
Two electrocytes in series will produce twice the potential if they are both stimulated at same time +
mV = 260 mV
3.0 V
1.5 V

34. What voltage does this give? Why wire it this way?
You get 1.5 V same as for a single battery. However, you get 2x as much current and so 2x operating life of whatever electronic device you are using.

35. Stacks of electrocytes add in series to increase total voltage in discharge
130 mV
Up to 700 V
520 mV …

36. Electric eel Can have up to 6000 electrocytes 6000 * 130 mV = 720 V
Can have more columns of electrocytes to deliver more current

37. Why would an animal use two columns?
Up to 700 V … …
Can supply more current - better for stunning or killing

38. Electric organs Evolved multiple times in fishes
Longer organs can generate larger potentials

39. Ohm’s law V = I R In freshwater, fewer salts in water
Water resistance, R is higher
Need higher voltage to get same current
I = V / R

40. Electric organ discharge, EOD
Temporal pattern varies between species
Here electrocytes are shown oriented relative to fish picture. Black dots are points of innervation by stimulating nerve cells. Waveform goes up when anterior of fish is positive relative to tail. If innervated from back, go positive first. If innervated from front, go negative first

41. EOD waveform control Skate Eel Knifefish Elephant fish
Depends on how electrocyte is innervated - determines polarity of EOD pulse. Skate and eel only have one side excitable so only get one polarity.
Gymnotiforms are excitable on both sides so go both positive and negative

42. Species specific discharges
Gymnotiforms are wave fish: emit high pulse rates of Hz
Mormyrids are pulse fish: emit variable rate pulses at Hz
Species live in murky water and are often nocturnal. Mormyrids using electrocommunication and sound while others just use electrocomm

43. Sodium channel activation shapes discharge

44. Electric discharge for different species
A knifefish
B brown ghost
C electric eel
D pintailed knifefish
E Mormyrid

45. Voltage gated sodium channel

46. Sites undergoing rapid change

47. Electro-communication
Some species can generate electrical signals
Probe environment
Communication
Stun prey
More species can detect electrical signals
Navigation
Prey detection

48. Coupling electrical signals to medium
Use EOD to communicate with nearby fish or to sample environment
Electric potential falls off as 1/distance2
But electric field is
So signals fall of as 1/ distance3 so only short range

49. Electric field around fish
Fish is a dipole - Head is positive, tail is negative
Can sense nearby objects as perturbation in their dipolar field

50. Perturbations to idealized monopole electric field
Distortion of electric field due to object with lower or higher resistance than surrounding medium

51. Reception of electric signals
More common to detect electric signals than to generate them
Fish: lamprey, rays, sharks, skates
sturgeon, paddlefish, coelocanths
catfish, gymnotiforms, mormyrids
Amphibians: salamanders, frogs, toads
Platypus

52. Electroreceptive monotreme
Platypus bill can detect electric fields

53. Electroreceptors Similar to hair cells of lateral line and ear
Stimulated by large voltage difference
To maximize sensitivity to electric field, want to sample it at two locations as far apart as possible

54. Further apart measure Measured voltage Proportional to resistance
V = IR
Voltage Resistor

55. Further apart measure Bigger voltage if More resistance V = IR
If R is 2x bigger
V is 2x bigger
Voltage Resistor

56. Electroreception
Imagine fish is resistor that is part of larger circuit
To maximize voltage sensed by fish, want its resistance to be larger than all other resistances

57. Salt water skates - ampullary receptors
Skates detect electric field gradient from ampullary organ -canal with openings
Use hair cells modified from lateral line
Good for low frequency signals
Hunting prey
Longer canals will have larger potential drop across them and so can detect smaller changes in potential.
Canals pointing in different directions will sense field oriented in different directions
Cluster will average out internal field from skate itself so differences seen only from outside skate

58. Cartilagenous fishes
Marine fish can detect fields as low as 5 x 10-9V/cm
Freshwater sensitivities are less
5 x 10-5 V/cm
This is like 9V battery over 2000 m or 1.2 miles
Longer canals will have larger potential drop across them and so can detect smaller changes in potential.
Canals pointing in different directions will sense field oriented in different directions
Cluster will average out internal field from skate itself so differences seen only from outside skate

59. Noise Freshwater teleosts less sensitive
0.005 V / cm
Freshwater noise is due to lightning
Even far away burst causes noise
Typically around 2 kHz

60. Swimming in magnetic field
Ocean currents moving through earth’s magnetic field generate electric field 10-9 to 10-7 V/cm
Rays may be able to navigate using these fields

61. Detecting prey Bodies of fish at different potentials
If move generate potentials (breathing)
Sharks and rays can detect these potentials, especially if they vary as breathing would

62. Gymnotiforms and mormyrids use tuberous receptors
Designed to detect high frequency voltage changes
Canal with high resistance plug
Can tune to respond to species specific frequency

63. Frequency of electroreception is tuned to species signal frequency
Receptive organ sensitivity
Highest sensitivity is point where threshold is lowest. This matches quite nicely the peak of signaling frequency.
Can also use receptors on each side of body to look at time delays, just as in hearing with two ears. This can help localize
Divide response of receptors to those cells that detect pulse rates - species specific communication and those cells that detect amplitude for electrolocation

64. Mormyrid electrocommunication