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Behavioural neuro > Electric fish > Flashcards

Electric fish Flashcards

1
Q

What is passive electrolocation? Example animals

A

Animal is electroreceptive only

Sharks, rays, catfish

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2
Q

What is active sense electrolocation? Examples

A

Animal generates its own electric field and can detect changes
Weakly electric fish and some strongly electic such as electric eel, ray and catfish

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3
Q

Animate source

A

Biological e.g. conspecifics, predators, prey of active sense animals

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4
Q

Inanimate source

A

Naturally occurring electric fields e.g. geomagnetic, electrochemical

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5
Q

Examples of elecroreceptive amphibians and a mammal

A

Salamanders and caecilians

Platypus

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6
Q

Evolutionary development and losses of electroreception…

A

Evolved by common ancestor of fish
Lost by many including teleoists
Re-evolved separately by mormyriforms and gymnotiforms
Re-evolved by monotremes (platypus)

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7
Q

How many groups of fish have convergently evolved electroreception? 4 examples and their names

A

Mormyriforms - african elephantfish
Gymnotiforms - south american knifefish
Malapteruidae - catfish
Torpediniformes - ray

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8
Q

Relative proportions of electroreceptive and electrogenic fish

A

25% electroreceptive
0.7% electrogenic
(out of 32000 species)

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9
Q

Examples within the two main groups of electric fish

A

Strongly electric
Electric eel, catfish and ray (~500-600V) to stun prey

Weakly electric
south american knifefish, african elephantfish (~10V) communication

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10
Q

Two types of electrical discharge. Which uses which?

A

Mormyriforms (african elephantfish) use pulse

Gymnotiforms (s.american knifefish) us wave

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11
Q

How is the EOD generated?

A

Electrocytes have -ve potential
Na/K exchanger pumps Na out
Impulse arriving causes ACh release
LGNCs open, Na influx is responsible for current

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12
Q

How are electrocytes arranged?

A

Into series to form electroplaques

Current flows +ve to -ve

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13
Q

How does stacking of electroctes aid function?

A

Formation of electroplaques allows for synchronous discharge and summation of current
They are insulated by connective tissue to force current through water (instead of body)

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14
Q

Which muscles generate EOD?

A

Tail muscle in weakly electric fish

Branchial muscles in electric rays

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15
Q

How do tentacled snakes bypass electroreception to catch fish?

A

They adopt a J shape and startle fish as they approach

Fish attempts to swim away but often swims into snakes mouth

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16
Q

How is EOD controlled?

A

By pacemaker nucleus in brain
Waveform is dependant on complexity of innervation of electrocyte
Monopolar in strongly electric
Bipolar or more in weakly electric fish

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17
Q

2 categories of electroreceptors

A

Ampullary (evolved in ancestral fish)
Tuberous (only in weak electric fish)
All are hair cells, mechanoreceptors

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18
Q

Describe the structure of an ampullary receptor (for passive electroreception)

A

A pit (lined with apical cells) filled with conductive gel and exposed sensory neurones at the bottom (on basement membrane)

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19
Q

Describe the functioning of ampullary receptors

A

Spontaneously active and sensitive to weak fields (1V in 2000km - marine. 1V in 10km - fresh water. Difference due to salt conductance in ocean)
Low frequency detection

20
Q

Signal transmission from ampullary receptors

A

Receptor cell depolarised
NT released
Causes EPSP in sensory neurone

21
Q

Describe the tuberous electroreceptor (for active electroreception)

A 
Sensory cells within basement membrane
Loose epidermal cover
Time markers detect frequency
Amplitude coders detect change in amplitude
(high frequency detection)
22
Q

Decribe the time marker in the tuberous electroreceptor

A

Single AP per EOD with fixed latency
1-35 receptor cells to one neurone
Used in passive electrolocation to detect fields of prey

23
Q

Amplitude coders

A

Bursts of spikes produced
Latency of first spike encodes the amplitude
Latency = time between EOD and first spike

24
Q

Key points of paper by Kalmijn

A

Shark put into agar chamber with covered flatfish
Shark located fish without vision
Little response to whiting pieces, none when smell removed with film
Bioelectric field of flatfish simulated with electrodes, eliciting same response
Shark preferred buried electrodes to visible whiting

25
Q

Which fish families engage in active electrolocation?

A

Mormyrids (amplitude coders) and gymnotids (amplitude and time-marker coders)

26
Q

Modification of brain areas for EOD

A

Reduction in other sensory areas

Somatotropic maps of electrosensitive body surface

27
Q

Challenges with electrocommunication

A

Mormyrids experience interference with own EOD: corollary discharge inhibition of timing marker in pulse fish
Gymnotiforms experience interference from conspecifics: jamming avoidance response

28
Q

Describe the jamming avoidance response

A

Two fish with similar frequencies will shift their frequencies to increase the difference between them, stopping the jamming of their electroreception

29
Q

What does curare do and what is its use?

A

Blocks mAChRs to silence self EOD

Allows fish to assess neighbor fish EOD and respond by changing pacemaker firing frequency

30
Q

Results of JAR

A

Self EOD frequency altered
Self fish monitors EOD frequency, not pacemaker firing for JAR
Uses receptors on body, not head to monitor EOD

31
Q

How do receptors respond differently to self and neighbour EOD?

A

Receptors are present to detect same strength and different strengths of EOD
Strength of neighbor EOD will vary as distance from source and angle of receptors will differ (receptors perpendicular to field least activated)

32
Q

Why is position of EOD source important to JAR?

A

Neighbour EOD electronically added to self EOD and played through self electrodes
Can’t perform JAR
Fish relies on differen filed characteristics cause by different EOD sources

33
Q

Role of ampullary receptors

A

Tuned into DC and low frequency
AC signals are not in EOD range
e.g. sharks use to detect low freq. DC fields of prey

34
Q

How do weakly electric fish use ampullary and tuberous receptors?

A

Detect the weakly electric fields produced by other fish

35
Q

What do tuberous receptors encode?

A

Frequency and amplitude of EOD

Two types: time markers, T, and amplitude coders, P

36
Q

Interpretation of self EOD

A

Time marker ‘T receptor’
Summation onto spherical cells
Convergence of info into Laminae of Torus semicircularis

37
Q

Sharks use specialised ampullary receptors to

A

Detect prey’s low frequency DC fields

38
Q

Weakly electric fish use their ampullary and tuberous receptors to

A

Detect weakly electric fields produced by neighbours

39
Q

What is an efferent copy?

A

Internal copy of outflowing movement-producing signal generated by the motor system. This inhibits expected sensory feedback. The EOD inhibits knollenorganes as the EOD is expected to hit them so don’t detect own EOD

40
Q

What is somatotopy?

A

Correspondence of an area of the body to a specific point on CNS. Receptor location represented as 4 somatotopic maps. Ampullary: 1. Tuberous projects to 3 maps.

41
Q

How do fish use active electrolocation for location?

A

Objects cause change in current flow. Area of active receptors indicate objects location relative to body
Insulators reduce current and conductors increase, forming somatotopic maps

42
Q

How do fish use active electrolocation for conductance?

A

Objects distort electric field created by EOD (amplitude increased or decreased)

43
Q

How do fish use active electrolocation for distance?

A

Closer objects cause a larger change in amplitude
Far object produces large image with low contrast
Near object produces small image with high contrast
Uses single stationary array of receptors

44
Q

How do fish use active electrolocation to determine capacitance?

A

Ability to store electrical charge
Organisms have high capacitance
Mormyrid (pulse) amplitude coders compare responses of A and B cells to determine capacitance
Gymnotids (wave) T receptors compare timing distortions at different positions on the body to determine capacitance

45
Q

How does capacitance change the EOD

A

Modifies shape but not timing of EOD pulses in pulse-type mormyrids
In wave time gymnotids, it modified timing of field relative to emission

46
Q

Other uses for EOD

A

Gender identification - males and females have different freq. ranges
Males modify EOD during courtship
Short low freq. chirps indicate aggression - long high freq. chirps indicate submissions

Behavioural neuro (4 decks)

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