NEURAL PATHWAYS FOR CARDIAC REFLEXES TRIGGERED BY EXTERNAL MECHANICAL STIMULI IN LARVAE OF BOMBYX-MORI

Stimuli applied to mechano-exteroceptors induce the following five types of reflex cardiac responses in larvae of Bombyx mori. (1) Tactile stimuli applied to sensillar setae of the anal proleg induce antidromic heartbeat. (2) The stimuli simultaneously inhibit orthodromic heartbeat. These stimuli increase the heart rate if applied during a phase of antidromic heartbeat. The visceral nerve arises from the frontal ganglion. The anterior cardiac nerves branching out of the visceral nerve were found to trigger antidromic heartbeat. Posterior cardiac nerves branching out of the visceral nerve are the inhibitory motor nerves which inhibit orthodromic heartbeat. These posterior cardiac nerves also contain motor nerves for alary muscles in the 2nd abdominal segment. (3) Contraction of the alary muscle increases heart tone and results in acceleration of antidromic heartbeat. (4) Tactile stimuli to the antennae accelerate orthodromic heartbeat. The motor pathway is through the paired dorsal nerves of the 1st abdominal ganglion in a segment which lacks a pair of alary muscles. (5) Contraction of the alary muscles in the 7th and 8th abdominal segments evoked by these stimuli contributes to acceleration of the orthodromic heartbeat. The motor pathways for this are in the paired dorsal nerves of the 7th abdominal ganglion.