Document Detail


Intrinsic rhythm and basic tonus in insect skeletal muscle.
MedLine Citation:
PMID:  650145     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The jumping muscle of orthopterous insects contains fibres that possess an intrinsic rhythm (IR) of slow contraction. The contributing fibres are generally synchronized, but as many as three or four pacemakers are present. The frequency, amplitude and duration of IR contractions fluctuate erratically over a 24 h period. Metathoracic DUM neurone bursts suppress IR for a few minutes. Other, unidentified dorsal neurones enhance its amplitude. In addition to IR, the extensor tibiae shows intrinsic basic tonus (BT). BT is relaxed for several s by low-frequency burst output from unidentified metathoracic dorsal neurones. DUM neurone bursts may enhance extensor BT, relax it, or leave it unaffected. The effects on IR of various regimes of activity in the slow extensor tibiae (SETi) and the common inhibitor (CI) axons were examined. CI affects IR when stimulated at frequencies above 2 Hz. It causes amplitude depression and reduced duration of individual IR contractions as well as increased frequency. At 30 Hz and above, CI completely suppresses IR. An enhanced IR contraction starts within a few milliseconds of the termination of a CI train. At low frequencies (below 10 Hz) SETi causes increased frequency and decreased amplitude of IR, with a depressed IR contraction following cessation of the SETi burst. At frequencies above 15 Hz the SETi-evoked contraction dominates tension development, though IR summates with it during the rising phase. In quiescent preparations not showing IR, SETi stimulation at 10 Hz often started up IR. Single SETi or FETi impulses can initiate an IR contraction, and cause altered phasing, with up to a quintupling of frequency. After a critical period has elapsed following the onset of an IR contraction, a single single impulse in any one of the three axons will terminate it abruptly. The early termination is followed by a reduced interval which is proportional to the reduced IR contraction time. The rhythm of accumulated readiness to go into an IR contraction is independent of the pacemaker rhythm that initiates the contraction.
Authors:
G Hoyle
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  The Journal of experimental biology     Volume:  73     ISSN:  0022-0949     ISO Abbreviation:  J. Exp. Biol.     Publication Date:  1978 Apr 
Date Detail:
Created Date:  1978-07-15     Completed Date:  1978-07-15     Revised Date:  2003-11-14    
Medline Journal Info:
Nlm Unique ID:  0243705     Medline TA:  J Exp Biol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  173-203     Citation Subset:  IM    
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MeSH Terms
Descriptor/Qualifier:
Animals
Female
Male
Membrane Potentials
Motor Neurons / physiology
Muscle Contraction*
Muscle Tonus*
Muscles / physiology*
Orthoptera / physiology*
Periodicity

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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