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Voluntary activation of spindle endings in human muscles temporarily paralysed by nerve pressure.
Author(s) -
Burke D,
Hagbarth K E,
Skuse N F
Publication year - 1979
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1979.sp012662
Subject(s) - isometric exercise , muscle spindle , efferent , anatomy , afferent , free nerve ending , pulmonary stretch receptors , contraction (grammar) , popliteal fossa , chemistry , postsynaptic potential , medicine , receptor , respiratory system
1. In normal human subjects, the afferent activity from muscle spindle endings in the pretibial muscles was recorded while a pressure block was applied to the peroneal nerve proximally in the popliteal fossa. 2. In five of ten blocks, spindle activity increased in attempted isometric voluntary contractions when the receptor‐bearing muscles were completely paralysed. In the remaining five blocks, voluntary effort still increased spindle activity when maximum voluntary power was reduced by more than 90%, but the ability to activate spindles voluntarily was lost with or slightly before block of the last motor units. When the ability to activate spindle endings in an attempted voluntary contraction was lost sympathetic efferent fibres remained unblocked. 3. It is concluded that the fusimotor effects seen during a voluntary contraction are mediated by myelinated fibres of small calibre which probably innervate intrafusal structures exclusively (gamma fusimotor fibres). There is no necessity to postulate that skeleto‐fusimotor (beta) fibres are responsible for the tight 'alpha‐gamma co‐activation' seen in man during voluntary contractions.