ISSN:
1432-1351
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary In spiders, stimulation of cuticular tactile hairs on the ventral aspects of proximal leg parts elicits reflex activity in certain leg muscles; contraction of these muscles raises the body. InCupiennius salei, using video film analysis, electromyography, and sensory recordings we studied the body-raising behavior and associated leg reflexes (i) in freely walking spiders, (ii) in animals tethered above a treadmill device, and (iii) in completely immobilized preparations. 1. Freely walking spiders abruptly (within 160 ms) raise their bodies by extending the legs when they touch a ventral flexible wire obstacle. The same animals collide with the obstacle when all tactile hairs on the sternum and on the ventral sides of all proximal leg segments have been removed (Fig. 1). 2. Body raising is also readily induced in tetheredCupiennius that are stimulated ventrally while standing on an air-suspended styrofoam sphere. Deflection of just one ventral hair can induce coordinated extension of all 8 legs (Fig. 2). Electromyograms reveal transient activity in several muscles that occurs almost simultaneously in all walking legs (Fig. 3). 3. Unlike the coordinated response of all legs in spiders tested on the treadmill, tactile reflex activity in spiders immobilized on their backs is confined to muscles of the particular leg being stimulated (‘local reflexes’). Again, deflection of a single tactile hair elicits activity in muscles such as the promotor/adductor of the leg coxa (muscle c2; Figs. 4, 7), which is involved in body raising. 4. The 3 bipolar, mechanosensory neurons innervating each tactile hair differ both in their rates of adaptation to maintained, step-like deflections of their hair shafts (Fig. 8) and in their frequency response to single and to repeated sinusoidal stimulus cycles. Tests with trains of sinusoidal hair deflections demonstrate that activity of one sensory-hair unit alone (unit ‘3’ in Fig. 8) is sufficient to drive the local tactile reflex in muscle c2. 5. Anterograde cobalt fillings of afferents from tactile hairs on the antero-ventral coxa (nerve ‘aCo’) into the fused subesophageal leg ganglia reveals a ventral group of fibers with ipsilateral, intrasegmental endings and a dorsal group with ipsilateral, plurisegmental arborizations in central neuropil (Fig. 9). A companion paper (Milde and Seyfarth 1988) identifies central neuronal correlates of the reflex activity described here.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01342636
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