The Effects of Fusimotor Activity on the Static Responsiveness of Primary and Secondary Endings of Muscle Spindles in the Decerebrate Cat

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  • PMP. B. C. Matthews
    P. B. C. Matthews
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Abstract
The effect of fusimotor activity on the static behaviour of soleus muscle spindle receptors in the decerebrate cat has been investigated by comparing their responses before and after ventral root section. The endings were classified as primary or secondary according to the conduction velocities of their afferent fibres. Their static behaviour was assessed by measuring their frequency of discharge at different lengths 0.5 sec after completion of a slow stretch at 3 mm/sec. Fusimotor activity increased the static responses of both kinds of ending; measured at physiological full extension, the average increase was slightly greater for primary than for secondary endings. The static responses of both kinds of ending tended to increase or decrease together when the level of fusimotor activity changed. The static sensitivity (slope of frequency‐extension relation) of both kinds of ending was commonly, but not invariably, increased by fusimotor activity. These findings, in conjunction with previous work, show that the behaviour of primary and of secondary endings is more alike under static than under dynamic conditions. This is discussed in relation to the possible functions of the secondary ending.

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