Sensing the Evnironment Flashcards
What are the types of electric sense?
Passive - Detects external fields. Electroreceptive.
Active - Generates its own electric field and detects changes. Electroreceptive and electronergic.
What are the types of passive electric sense?
Animate - Detection of bioelectricity generated by other organisms.
Inanimate - Detecton of naturally occurring electric fields in the environment.
Give examples of naturally occuring electric fields.
Electrochemical
Geomagnetic
Which organisms exhibit passive electric sense?
Sharks Skates Rays Catfish Electric fish types
What are the types of active electric sense?
Animate - Sensing other members of the species, predators and prey.
Inanimate - sensing anything with an electrical conductivity different to that of water.
Which organisms exhibit active electric sense?
Weakly electric fish Some strongly electric fish: Electric eel Electric ray Electric catfish
What types of vertebrates is electroreception present in?
Jawless fish Cartilaginous fish Bony fish Amphibians Mammals
Which jawless fish use electroreception?
Lampreys
Which cartilaginous fish use electroreception?
Sharks
Skates
Rays
Which bony fish use electroreception?
Sturgeons
Catfish
Which amphibians use electroreception?
Salamanders
Caecilians
Which mammal uses electroreception?
Platypus
Describe the evolutionary history of electroreception.
Evolved by common ancestors of fish
Lost by many bony fish
Re-evolved separately (together with electrogenicity) by mormyriform and gymnotiform fish.
Re-evolved by monotremes - platypus.
What are the 5 groups of electroceptive/genic fish? Give an example.
Mormyriforms - Elephantnose fish Gymnotiform fish - Electric eel. Knifefish Malapteruridae - Electric catfish Uranoscopidae - Stargazers Torpediniformes - Electric ray
What % of fish are electroreceptive?
25%
What % of fish are electrogenic?
0.7%
What are the electrogenic properties of strongly electric fish?
Live mainly above equator.
500-600V discharge.
What are the electrogenic properties of weakly electric fish?
Live mainly below equator.
10V discharge.
What is the discharge of strongly electric fish used for?
Stunning prey
What is the discharge of weakly electric fish used for?
Detection of perturbations in own electric field.
Used for location of prey/obstacles and communication.
What are the 2 types of discharge of weakly electric fish and which fish use them?
Wave - Most american knifefish
Pulse - Most african knifefish
What are electrocytes?
Modified muscle cells of the electric organ of electric fish.
How are electrocytes modified?
Negative on the inside.
Describe the stages of electric organ discharge (EOD).
Impulse arriving along the motor neuron causes release of ACh onto one side of the cell.
ACh binds to ion channels in the membrane.
Channels open causing depolarisation and flow of current.
Electrocytes arranged in battery-like series
Current flows from +ve to -ve side causing a synchronoud discharge.
What does the waveform of the EOD depend on? Give examples.
Innervation of electrocytes:
Monopolar - Strongl electric fish
Bipolar - Weakly electric fish
Why do electrocytes not contract?
Contraction decoupled from excitation.
What are electroplaques?
Stacks of electrocytes
How do fish ensure current flows through water and not bodily fluids?
Insulate body parts from the current.
Compare the location of electroplaques in fish.
WEF - By tail muscles
SEF - By branchial muscles
How is EOD controlled?
Pacemaker nucleus in the brain.
What are the types of electroreceptors?
Ampullary
Tuberous
Compare the evolutionary history of both types of electroreceptors.
Ampullary - evolved in ancestral fish. Now in all electrosensitive fish and elasmobranchs.
Tuberous - Evolved in WEF. Mormyriforms and Gymnotiforms only.
Describe the structure of ampullary receptors.
Pit filled with conductive gel and an exposed sensory neuron at the bottom.
What are the properties of ampullary receptors?
Spontaneously active
Sensitive to weak electric fields of 1V in 2000km of marine water or 10km fresh water.
Detect 0-30Hz
What is the function of ampullary receptors?
Passive electrolocation.
What are the properties of tuberous receptors?
Respond to discharges of electric organs.
What is the function of tuberous receptors?
Encoding information about frequency and amplitude of electric fields.
What are the types of tuberous receptors?
Time markers
Amplitude coders
What is the function of time markers?
Detection of frequency
Passive electrolocation
How do time markers detect frequency?
1-35 receptors per neurone.
Receptors cells fire single AP per EOD
Electrical synapses connect to the neurone for fast transmission.
What is the function of amplitude coders?
Detect change in amplitude
Active electrolocation
How do amplitude coders detect amplitude?
Latency of the 1st spike encodes amplitude
Shorter latency - higher amplitude.
What are the types of amplitude coders?
A
B
What are the components of the octavo-lateral sensory system?
Electroreceptors Hearing receptors Equilibrium receptors Gravity receptors Water current receptors
What is the risk associated with EOD in pulse fish? How is it avoided?
Interference with own EOD.
Corollary discharge inhibition of timing marker.
What is the risk associated with EOD in wave fish? How is it avoided?
Risk of interference from other conspecifics.
Jamming avoidance response.:
Frequencies of the two fish summate to create a wave within the wave.
Fish with higher frequency wave will shift its frequency even higher
Fish with lower frequency will shift its frequency lower.
What monitors the frequency of fish’s EOD?
External receptors
How is own EOD distinguished from others’?
Receptors will distinguish own EOD because the strength of the signal will be equal around the circumference of the fish
EOD of other fish will have different strengths around the circumference and the angle of the signal will be different too.
What is the role of tuberous receptors in electrocommunication?
Collection of information about surrounding EODs.
Why can’t ampullary receptors collect EOD info?
Ampullary receptors tuned to DC which is not in EOD’s range.
Tubular receptors are tuned to AC which is in EOD range.
How do time markers detect self and neighbouring EOD?
Fire action potentials when the amplitude of the incoming EOD goes from +ve to -ve.
Signal is synapsed onto the hindbrain’s somatotopic maps.
Signal summates onto spherical cells.
Frequency info passed onto Laminae of Torus semicircularis.
How do amplitude coders detect self and neighbouring EOD?
Fire action potentials in proportional frequency to the amplitude of the EOD.
Signal synapsed onto somatotopic maps of the hindbrain.
Excitation of basilar pyramidal cells
Inhibition of non-basilar pyramidal cells
Amplitude info passed onto laminae of torus semicircularis.
Describe the signalling pathways from torus semicircularis.
Signal passed onto nucleus electrosensorius.
Stimulatory signal activates PPnG in the prepacemaker nucleus which passes the signal onto pacemaker cells in the pacemaker nucleus.
PAcemaker cells transmit the signal to relay cells which activate the electric organ.
An inhibitory signal inhibits the SPPn in the pre-pacemaker nucleus.
Signal not passed onto relay cells of the pacemaker nucleus.
Relay cells reduce EOD frequency from the electric organ.
Describe the pathway of corollary discharge inhibition.
Motor output creates a copy which is used to inhibit the expected feedback from the action of the electric organ.
This means that the EOD inhibits knollerorganes at the same time its about to hit them.
This way fish do not detect own EOD.
How is the EOD information processed n somatotopic maps?
Electroreceptor location is represented as 4 somatotopic maps in the electrosensory lateral lobe (ELL) in the hindbrain.
1 map contains ampullary receptor projections
3 map contain tuberous receptor projections.
Receptor arrangement also preserved in the midbrain.
Which features are detected by active electrolocation?
Location Conductance Distance Capacitance Electrocommunication
How is location detected via active electrolocation?
Object within the EOD changes the current flow.
Insulators reduce current
Conductors increase current
Area of active receptor picking up the returning signal is detected in the somatotopic map and the relative position of the object can be determined.
How is electrolocation used to sense conductance of an object?
Objects distort the electric field
Conductors increase EOD amplitude
Insulators decrease EOD amplitude.
How is distance of an object determined using electrolocation?
Closer objects cause a greater change in amplitude.
Distant objects activate more receptors which means their “shadow” is more spread out.
Shadow of distant objects has less contrast because the change in amplitude that they cause is smaller.
Distance calculated slope-to-amplitude ratio.
How is electrolocation different to stereoscopic vision/auditory perception and echolocation?
Uses a single array of receptors.
No time measurements are taken.
What is capacitance and how does it compare in living organisms and inanimate objects?
Storage of charge
Living organisms have high capacitance
Inanimate objects have low capacitance.
How is capacitance detected by pulse fish?
Mormyrids use amplitude coders (mormyromast receptors) to compare responses of A and B cells to determine capacitance.
Capacitance modifies shape of EOD.
How is capacitance detected by wave fish?
Gymnotids use time markers (T-receptors) to compare timing distortions at different positions on the body.
Capacitance modifies the timing of the field relative to emission.
What is the function of electrocommunication?
Species identification
Gender identification
Courtship
Aggression
How are species identified by electrocommunication?
EOD is species-specific
May be pulse-like or wave-like
EODs of different species have different frequencies.