Thoracic Connections Between Crayfish Giant Fibres and Motor Giant Neurones Reverse Abdominal Pattern

Abstract

ABSTRACT The escape tail-flip of the crayfish is ‘commanded’ by two bilaterally paired sets of giant fibre (GF) interneurones, the lateral giant (LG) and medial giant (MG) (see e.g. Wine, 1984, for a review). The two classes of GF respond to different stimuli and initiate tail-flips with different kinematic forms. An arousal stimulus applied to the front of the animal initiates a spike in the MG system, and this causes a tail-flip that drives the animal directly backwards, away from the stimulus. An arousal stimulus applied to the rear of the animal initiates a spike in the LG system, and this causes a tail-flip that drives the animal upwards and forwards, again moving it away from the stimulus. The major motor output path from the GFs is through monosynaptic rectifying electrical connections to a class of powerful trunk flexor motor neurones called the motor giant (MoG) neurones (Furshpan and Potter, 1959a). There is one MoG neurone in each hemisegment of the thorax and abdomen.