Abstract
The distal portion of the flexor muscles powering tailspine movement in the horseshoe crab is innervated by separate sensory and motor nerves. Records from the sensory nerve of an undisturbed preparation show tonic afferent activity which is increased by movement of the tailspine. Splitting the nerve, which randomly isolated small bundles of fibers, permitted identification of individual sensory units. Imposed lengthening or shortening of the passive muscle elicited unidirectional “movement” fibers. Another class of units fired only upon active contraction and showed increased activity with increasing muscle length. These units appear to be series tension receptors. Each of the receptor types observed showed phasic and tonic activity. Reflex motor activity could be elicited by stimulation of the sensory nerve, although the identity of the afferents eliciting this activity was not determined. Methylene blue staining showed multipolar and bipolar neurons near the muscle insertions, suggesting that these might be the receptors responsible for the observed sensory activity.
Published Version
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