Motor Coordination in Crustacean Limbs
Over the past decade, it has become generally accepted that the cyclic patterns of motor neuron (MN) discharge which underlie rhythmic behavior can be generated in the absence of sensory feedback (Evarts, 1971; Grillner, 1975; Kennedy and Davis, 1976; Selverston et al., 1976). Nevertheless, the motor output observed in behaving animals is quite variable and capable of considerable adaptive response. Clearly, central oscillators are under the control of command systems (Hughes and Wiersma, 1960a,b; Ikeda and Wiersma, 1964; Davis and Kennedy, 1972a,b; Bowerman and Larimer, 1974a,b). The question of how central oscillators interact with the mechanical systems which they control has received much less attention (Kennedy and Davis, 1976). Here I shall review the role of proprioceptive feedback in the modulation of posture and locomotory behavior in decapod crustaceans. Crustaceans offer several technical advantages in the study of central peripheral interactions: First, the behavior of crustacean limbs is easily quantifiable in terms of joint position, movements, and tension and is interestingly variable. Second, the crustacean limb is controlled by a restricted number of identifiable motor units (Wiersma, 1961; Atwood, 1967a, 1973a). Third, crustacean appendages possess a rich complement of discrete receptor organs, each of which is sensitive to a limited range of inputs and can be studied in isolation (Alexandrowicz and Whitear, 1957; Whitear, 1962; Bullock and Horridge, 1965; Wales et al., 1970). Last, altered sensory feedback can cause major changes in the output of the central oscillators, and these phenomena can presumably be explained in terms of interactions between the different neuronal components.
KeywordsMotor Coordination Bipolar Cell Flexor Muscle Extension Unit Power Stroke
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