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Spatial and Temporal Changes in the Coupling of Cockroach Spiracles to Ventilation
1 Department of Zoology, University of Oxford
1. Spiracles 10 of Blaberus giganteus can be coupled with ventilation so as to open either with inspiration or with expiration. Similar activity in a mantid has been shown to produce either anteriorly or posteriorly directed ventilating airstreams in longitudinal tracheae. Switching between the two modes of coupling, which can be controlled experimentally, may pass through a maintained transitional stage when both forms occur.
2. Coupling with inspiration involves symmetrical activity in opener muscles of left and right spiracles. However, when coupled to expiration only one spiracle is active. The unilateral application of electrical or mechanical stimuli to various regions of the body causes the spiracle on that side to open with expiration.
3. Medially divided abdominal ganglia still joined to the CNS through the connectives are capable of both forms of coupling. It is suggested therefore that reciprocal inhibitory coupling between coordinating interneurones and not between motor neurones accounts for asymmetrical activity when the spiracles are coupled to expiration.
4. Spiracles 3, 6, 7 and 8 act in a similar way to spiracle 10 but have higher thresholds. Spiracles 4, 5 and 9 are associated with glandular structures and their activity is different. They may allow chemicals to be expelled through them when the insect is strongly stimulated.
5. A model is presented which accounts for some aspects of the activity of spiracles 10.
Submitted on January 10, 1973
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