The Neuromuscular System Of The Flexible Arm Of The Octopus: Physiological Characterization. Henry Matzner, Yoram Gutfreund and Binyamin Hochner. Department of Neurobiology and Center for Neuronal Computation, Institute of Life Sciences, Hebrew University, Jerusalem 91904, Israel.
APStracts 6:0550N, 1999.
The octopus arm is an outstanding example of an efficient boneless and highly flexible appendage. We have begun characterizing the neuromuscular system of the octopus arm in both innervated muscle preparations and dissociated muscle cells. Functionally antagonistic longitudinal and transverse muscle fibers showed no differences in membrane properties and mode of innervation. The muscle cells are excitable, but have a broad range of linear membrane properties. They are electrotonically very compact, so that localized synaptic inputs can control the membrane potential of the entire muscle cell. Three distinct excitatory neuronal inputs to each arm muscle cell were identified; their reversal potentials were extrapolated to be about -10mV. These appear to be cholinergic as they are blocked by hexamethonium, dTC and atropine. Two inputs have low quantal amplitude (1-7mV) and slow rise times (4-15 ms), while the third has a large size (5-25mV) and fast rise time (2-4ms). This large synaptic input is most likely due to exceptionally large quantal events. The probability of release is rather low, suggesting a stochastic activation of muscle cells. All inputs demonstrated a modest activity-dependent plasticity typical of fast neuromuscular systems. The pre- and postsynaptic properties suggest a rather direct relation between neuronal activity and muscle action. The lack of significant electrical coupling between muscle fibers and the indications for the small size of the motor units suggest that the neuromuscular system of the octopus arm has evolved to ensure a high level of precise localization in the neural control of arm function.
Received 9 July 1999; accepted in final form 28 October 1999.
APS Manuscript Number J558-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999