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[Th025] Citation: Abstract
A mechatronic structural model of the mammalian muscle spindle Ia
response was developed and used to investigate neuromechanical
mechanisms contributing to individual spindle dynamics and the
information content of spindle ensemble response. Engineering
specifications were derived from displacement, receptor potential and
Ia data in the muscle spindle literature, allowing reproduction of
core muscle spindle behavior directly in hardware. A linear actuator
controlled by a software muscle model replicated intrafusal
contractile behavior; a cantilever-based transducer reproduced sensory
membrane depolarization; a voltage-controlled oscillator encoded
strain into a frequency signal. Results of engineering tests met all
performance specifications. Data from the biological literature was
used first to tune the model against 5 measures of ramp and hold
response, then to validate the fully tuned model against ramp and
hold, sinusoidal and fusimotor response experiments. The response with
dynamic or static fusimotor input was excellent across all studies.
The passive spindle response matched well in 5 of 9 measures. Dynamic
intramuscular strain data from 28 locations on the surface of a
contracting rat medial gastrocnemius was sent sequentially through the
model to reconstruct the Ia ensemble response of a large population of
muscle spindles. Results showed that under dynamic fusimotor
stimulation, the ensemble significantly increased Ia correlation to
whole muscle kinematic inputs and that homogeneously distributed
dynamic fusimotor stimulation increased Ia ensemble correlation to
muscle velocity in a dose-dependent manner. Proposed mechanisms
include decorrelation of spindle noise by intramuscular strain
inhomogeneities and fusimotor-dependent noise and nonlinear gains, as
well as fusimotor-dependent velocity selectivity. Potential
applications for the robotic model include basic science motor control
research and applied research in prosthetics and robotics.
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Updated: Tue Jul 15 23:54:51 2008
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