32 The Physiology of Sense Organs 



classics in the neurophysiological literature, are taken from the 

 work of Eyzaguirre and Kuffler,^' who were the first to 

 investigate this preparation with microelectrodes. In these 

 experiments the potential changes were detected by means of a 

 recording pipette inserted in the soma. The potential change 

 observed therefore consisted of soma action potentials as well as 

 depolarizing receptor potentials caused by stretch of the MRO 

 and deformation of the dendritic branches in the associated 



Fig. 12. Intracellular records from a slowly-adapting stretch 

 receptor neuron of the crayfish, showing action potentials super- 

 imposed upon stretch-induced receptor potentials. (A) Stretch 

 increased and then maintained at low levels to show regularity of 

 discharge. (B) Stretch gradually increased between first arrow and 

 vertical line, then maintained for several seconds (missing part 

 of record). Note slight hyperpolarization following relaxation. 

 (From Eyzaguirre and Kuffler,^'' Fig. 5.) 



sensory neuron. It was found that the amplitude of the receptor 

 potential could be finely controlled by the degree of passive 

 stretch applied to the receptor muscle. This effect appeared 

 uncomplicated by impulse activity until it reached an amplitude 

 of about ID mV (in slowly-adapting cells) or 20 mV (in fast- 

 adapting ones). The duration of the receptor potential in the 

 slowly-adapting neuron was essentially equivalent to that of the 

 applied stimulus. When an applied stretch was sufficiently 

 intense, nerve impulses appeared in the electrical records (fig. 12). 

 Although the regularity of the discharge tended to be less constant 

 at threshold than at higher amplitudes of depolarization, control 



