Electric Fish

Electric Fish
I)
Electroreception
A) Receptors – modified hair cells – sense electric fields
generated by other animals or objects in environment
B) Weakly electric fish – emit electric field (electric organ) and
can sense distortions in this field produced by objects in
external environment
C) Strongly electric fish – electric eels - predation
(Africa)
(South America)
II. Physiology
A) Electric Field Characteristics
Constant
Voltage
Current
Flow
Undistorted electric field
Insulator
Conductor
Heiligenberg, J Comp Physiol
87:137-164, 1973
Distorted Electric Field
B) Electric Organ
1) Modified Muscle Cells – stacked end to end
2) Generating an Electric Field (Electric Organ Discharge – EOD)
+70
-80
excitable
0
-80
inexcitable
-150
0
-150
-80
-80
0
0
2) Generating an Electric Field
+70
-80
excitable
0
-300
-80
-230
inexcitable
-150
0
-150
-80
-80
0
0
3) Electroreceptors
a) Modified hair cells – sensitive to
amount of current across skin
b) Two types –
i) ampullary organ – in all fish
that have electrosensation
ii) tuberous organ – only in fish
that generate an EOD
c) Cranial Nerve – Lateral Line
Nerve
Lateral Line
Nerve
III. Anatomy
A) Lateral Line nerve – near 8th cranial nerve
B) Electrosensory lateral line lobe –
C) Torus semicircularis (homologous to inferior colliculus)
1) projection to tectum and tegmentum
D) Nucleus electrosensorius
E) Prepacemaker nucleus
F) Pacemaker nucleus
G) Electromotor neurons (ventral horn of spinal cord)
IV Electrosensation – ampullary receptors in weakly electric fish
A) The problem – how to distinguish external electric field from the one
generated by the fish?
1) Proposed solution – reafference – efference copy – corollary
discharge
B) Experiment – CC Bell and colleagues
1) Record from ELL
2) Curarize animal –
blocks EOD
3) Record from motoneuron –
command signal - C
4) Generate artificial electric
field - STIM
Bell, J Neurophysiol 47: 1043-156, 1982
record
C) The Result
Command Only
Invert Electric Field
Paired
Later
Command Only
Later again
1) Motor command and sensory consequence must be in temporal proximity