Comparative analysis of an excitatory motor unit in crustaceans
The leg stretcher muscle motor unit was examined in five different decapod crustaceans (Gecarcinus, Grapsus, Goniopsis, Homarus andPanulirus) with the objective of establishing interrelationships between nerve terminal and muscle fiber properties.
In each species, nerve terminals varied greatly in their capacity for facilitation of transmitter release (Fe), muscle fibers varied with respect to sarcomere length (SL), and a wide range of excitatory postsynaptic potential amplitudes (EPSPs) was observed.
Fe was inversely correlated with EPSP amplitude and SL in all five species. Therefore, selective matching of nerve terminals to muscle fibers appears to be a general rule of organization in the stretcher excitatory motor unit in decapod crustaceans.
A correlation was found between the Fe type of terminal and total depolarization of the sarcolemma at frequencies up to 20 Hz for all species. No such correlation was evident above 40 Hz for any species, indicating that all muscle fibers in the motor unit are activated to approximately the same extent at the higher levels of activity.
Possible consequences of these interrelationships for the performance of the motor unit are discussed.
KeywordsMuscle Fiber Comparative Analysis General Rule Motor Unit Nerve Terminal
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