Fig. 5. (A) Lateral view of the spatial organisation of thoracic and abdominal stretch receptors. Segmental stretch receptors are located on the dorsal side and extend axons that run towards the central nervous system (CNS) via nerve 3 (N3). Note that, as in crayfish, the axons of the abdominal stretch receptors project to the eighth thoracic ganglion. (B) The CNS and central projection of the axon of TSR-2. The CNS is depicted dorsally, and the CNS posterior to TG3 is not drawn, and the oesophageal connectives are interrupted. Ascending and descending central projections of the axon of TSR-2 are shown (camera lucida drawing). This was revealed by electrophoretically applying Lucifer Yellow to the centrifugal cut end of N3. (C) Ventral view of the organisation of thoracic stretch receptors. Thoracic stretch receptors are located dorsally and bilaterally. Dendritic branches from the receptor cell of TSR-1 innervate the extensor muscle, while those of TSR-2 entwine with the receptor muscle-like strand, which is exaggerated in size. TSR-3 to TSR-7 have two receptor cells and a single receptor muscle. AS, abdominal segment; ASR, abdominal stretch receptor; TS, thoracic segment; TSR, thoracic stretch receptor; ROS, rostrum; Deutero, deuterocerebrum; Mx, maxillary nerve; Proto, protocerebrum; Trito, tritocerebrum; TG, thoracic ganglion.
