Forelimb Proprioceptors Recorded during Voluntary Movements in Cats
Most of our knowledge regarding proprioceptive activity in freely moving cats comes from recordings from hindlimb afferents. Currently, little is known about this activity in the forelimbs. One might speculate that this could be extrapolated from existing hindlimb data. Indeed, assuming similarities in receptor morphology and sensitivity, this may be true for receptors not under efferent control. However, there are several reasons to suspect that this extrapolation is less secure for the muscle spindle receptor; 1) The forelimb performs reaching and manipulative tasks requiring more supraspinal control than hindlimb movements (Pettersson, 1990), 2) Supraspinal sites branch more extensively to cervical regions (Kuypers & Martin, 1982), 3) Presumed spindle afferents in arm and hand muscles of monkeys generally had more complex firing characteristics than cat hindlimb spindles (Schieber & Thach, 1985), 4) There may be differences in spindle receptor morphology, as demonstrated between hindlimb and neck musculature (Dutia, 1991). A knowledge of spindle receptor firing patterns from the cat forelimb may also shed some light on the differences in firing rates in humans (peak approx. 85 imp/s) compared to cats (peak approx. 600 imp/s). We have therefore been developing a technique to obtain forelimb afferent recordings in awake cats.
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