EFFECTOR MECHANISMS 399 



in central neurones aided by a field effect from the electroplates initially 

 excited. 



Membrane potentials have been measured in single electroplates of the 

 electric eel (Electrophorus). The resting potential is 84 mV across each 

 face, the inside of the cell being negative to the exterior. In this animal 

 only the posterior face of the plate is excitable; on stimulation a large spike 



.. .A,. .... 



Fig. 9.20. Electrical Discharges in Torpedo torpedo 

 (a) Simultaneous recording of nervous discharge and corresponding reflex discharge 

 in fragments of the electric organ connected to the c.n.s. Reflex discharge of the electric 

 organ above; nerve impulses below, with discharge artifact, (b^ Responses to stimula- 

 tion of the electric lobe by a brief shock. Reception in the two symmetrical organs. 

 (b 2 ) Stimulation of the electric lobe by prolonged current. Time trace in msec. (From 

 Albe-Fessard (5).) 



is produced, at the peak of which the membrane potential is reversed by 

 67 mV. During activity the voltages across the opposite faces add together, 

 each electroplate contributing 151 mV (on open circuit) to the total 

 discharge. The electrical response of the electroplate appears to be 

 fundamentally similar to that of a muscle fibre. An impulse is propagated 

 along its length at a velocity of 1 -7 m/sec. It is likely that, as in muscle, the 

 electrical energy liberated during discharge is derived from the migration 



