Summary
The dynamic responses of spindle receptors to large ramp changes in length cannot be broken down into length, velocity and acceleration components. Instead, it is shown that, except for a brief transient phase associated with the initial burst, response is proportional to the product of a velocity-dependent and a length-dependent term. The velocity-dependent term is approximately ν0.3 for both primary and secondary endings, both in the presence and in the absence of spontaneous fusimotor activity. For the majority of receptors, length dependence is well characterised by an upwardly offset straight-line relation between discharge rate and muscle length. It seems likely that this peculiar form of relation derives from the mechanical properties of intrafusal muscle fibres. Regardless of the mechanism, the relation places many interesting constraints on theories of motor control.
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References
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Houk, J.C., Rymer, W.Z., Crago, P.E. (1981). Nature of the dynamic response and its relation to the high sensitivity of muscle spindles to small changes in length. In: Taylor, A., Prochazka, A. (eds) Muscle Receptors and Movement. Palgrave Macmillan, London. https://doi.org/10.1007/978-1-349-06022-1_4
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DOI: https://doi.org/10.1007/978-1-349-06022-1_4
Publisher Name: Palgrave Macmillan, London
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