The anatomy, ultrastructure and mechanical properties of the locust metathoracic femoral chordotonal organ
2014-12-15T10:33:17Z (GMT) by
1. This thesis examines the anatomy, ultrastructure and mechanical properties of the metathoracic femoral chordotonal organ (mtFCO) in the locusts Schistocerca gregaria and Locusta migratoria. Some measurements were also made on the mtFCO of the giant grass hopper Tropidacris collaris. The mtFCO is of interest because of its complex mechanical linkages (the apodeme complex, Shelton et al. 1922) and its wide range of receptor response types (Zill, 1985; Field and Pfluger, 1989; Matheson, 1990).;2. Electron microscopy has been used in conjunction with modern image analysis techniques to provide the first comprehensive description of the composition of each of the mtFCO's mechanical linkages.;3. This thesis provides the best evidence so far that the mtFCO of the locust is formed from two fused scoloparia, each of which is innervated by a separate branch of the CO nerve (nerve 5b1). It has been shown for the first time that the neurones of the mtFCO can be subdivided consistently into 6 discrete populations, each of which is innervated by a separate bundle of axons. Neurone size, shape and orientation vary between the populations.;4. The dendrites of the sensory neurones terminate the pairs in specialised scolopale cells in a manner similar to that previously described in other insect COs. This thesis provides the first description of the dendritic distortions which occur upon stimulation of an unfixed sense organ.;5. Biomechanical investigations have revealed that the mtFCO is a viscoelastic system. The results from this thesis suggest that the organ's mechanical properties are likely to be partly or wholly responsible for two documented phenomena common to all COs; hysteresis of the sensory output in response to cyclic elongation/relaxation (Burns, 1974; Matheson, 1990, 1992) and adaptation in firing rate following a step displacement (Usherwood et al., 1968; Theophilidis, 1986).