EXCITATORY AND INHIBITORY PROCESSES 



307 



V V W W 







Fig. 16. Post-inhibitory polarization, a (a). Stretched slow receptor cells dis- 

 charge at 7/sec. Intracellular records, a (b). Inhibitory impulse train at 45/sec 

 inhibits discharge, a (c). Inhibitory impulse train at 150/sec causes longer 

 inhibitory period. End of inhibition potential is followed by a delayed polariza- 

 tion phase. A (d). Inhibitory train at 200/sec. A delayed polarization potential is 

 further increased, b (a). Extracellular records. Another slow receptor cell under 

 light stretch. Inhibitory train at 100/sec sets up repolarization during stimulation 

 followed by additional delayed polarization, b (b). Stimulation at 50/sec causes 

 polarization and little post-inhibitory effect, b (c). Longer inhibitory train at 

 50/sec sets up marked post-inhibitory polarization phase, b (d). Less stretch 

 on cell. Inhibitory impulses at 50/sec set up smaller polarization potential during 

 train. Time, 10 c/s. (From Kuffler and Eyzaguirre, /. Gen. Physiol. 39 : 155-184, 



1955.) 



in a number of preparations. After inhibition has been withdrawn the rate 

 of rise of the pre-potential increases and the discharge rate may be transiently 

 accelerated in some slow receptors. This phenomenon is particularly well 

 seen in rapidly adapting neurons which have been stretched near to their 

 firing level. A short burst of inhibitory impulses may initiate one or more 

 afferent discharges in a quiescent receptor cell (see Fig. 17). This is probably 

 a post-inhibitory rebound phenomenon since inhibition removes effectively 

 the depolarization produced by stretch. If the transmitter effect produced by 

 inhibitory impulses is suddenly removed, this will be equivalent to applying 

 stretch very quickly. 



