INTEGRATIVE PROPERTIES OF A REFLEX MOTONEURON IN BRAIN OF CRAB CARCINUS MAENAS

1. A proximal portion of the reflex eye-withdrawal motoneuron in the crab brain (Carcinus maenas) does not conduct spike potentials but acts instead as an integrating sink for signals coming into it from smaller side branches. 2. Stimulation of the primary sensory input to the reflex evokes an excitatory depolarization in this integrating segment. The excitatory depolarization is made up of summed spike potentials occurring in small side branches of the integrating segment. 3. The reflex can be inhibited and also excited by axons in the ipsilateral oesophageal connective. The inhibitory, and probably also the excitatory inputs, act post-synaptically, that is, on the motoneuron. 4. It is suggested that whereas the excitatory synaptic contacts are made at the ends of thin, excitable side branches extending from the integrating segment, inhibitory contacts are made directly on the main body of the integrating segment. © 1969 Springer-Verlag.