Abstract
Physiological properties of isolated gastrocnemius motor units were measured in normal juvenile postmetamorphic Xenopus frogs and in a group of juvenile animals with a single bilaterally innervated hindlimb. The aim of this study was to evaluate changes to the organisation of the motor unit when the muscle is hyperinnervated. Animals with a single bilaterally innervated hindlimb have previously been shown to support up to twice the normal number of motoneurons projecting into a single hindlimb. Under these circumstances there was a lowering of average neuromuscular efficacy (as judged by motor unit twitch/tetanus ratio) in comparison with normal age-matched siblings. Motor units with neurons in the lateral motor column contralateral to the remaining hindlimb were indistinguishable from those originating ipsilaterally. There is a wide range of safety margins for neuromuscular transmission at the various terminals of individual frog motor units, and comparison of motor unit contraction times with twitch/tetanus ratios showed that under pressure of hyperinnervation, motoneurons tend to retain their safest terminals on muscle fibres with fast contraction times.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
