This chapter focuses on the spinal mechanisms controlling stepping and scratching movements of the cat's hind limb. The reasons for considering scratching are two-fold: first, the stepping and scratching motor patterns have many features in common, suggesting that their control mechanisms share basic elements. Second, the mechanisms for scratching are easier to analyse because of their relative simplicity, since only one limb performs rhythmic movements, in contrast to stepping, where all four limbs participate. It is well established that rhythmic activity with an efferent motor pattern similar to stepping for each of the hind limbs, and with bilateral alternation, can be generated by the spinal cord in the absence of sensory feedback. This was demonstrated in the deafferented cat, which is after transection of all dorsal roots in the lumbosacral enlargement of the spinal cord. When deprived of sensory feedback, the limb controller can generate efferent patterns closely resembling rhythmical movements of the limb.
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