Components of a Response Programme Involving Inhibitory and Excitatory Reflexes in the Surf Clam

Abstract

1. Electrical records from ganglion cells in the central nervous system and from intact muscle groups controlling siphon retraction and shell-valve adduction have revealed qualitative similarities in the response characteristics of two neurone-effector systems following stimulation of tactile afferents. 2. Simultaneous electrical records from neurones and muscle indicate that Type I ganglion cells are motoneurones to the fast portion of the posterior adductor muscle. 3. The waveform and polarity of the post-synaptic responses of Type 1 cells depend critically upon the intensity of stimulation over intact sensory pathways. High-intensity input transiently excites the fast portion of the adductor; low-intensity input inhibits the adductor motoneurones. The input organization of Type I neurones therefore permits discrimination of stimulus magnitude and thus controls the characteristics of the response programme.