Over the past several decades, the functional organization of motor systems, and in particular those controlling rhythmic movements, has been viewed in the context of two conceptual hypotheses. The observation that many rhythmic motor patterns and behaviors could persist in the absence of phasic sensory feedback led to the idea of a central pattern generator (CPG). The CPG is envisioned as a group of central neurons that generates a sequence of temporally and spatially coordinated activity. It is now clear that most, if not all rhymic behaviors have as their basis a central pattern generator (Delcomyn, 1980). The second major hypothesis has been the concept of the “command” neuron or system. This idea is founded in the work of Wiersma and Ikeda (1964), who observed that stimulation of certain neurons in the crayfish could elicit rhythmic movements of the swimmerets. Despite attempts to define a command neuron by explicit criteria (Kupfermann and Weiss, 1978), the term is most commonly used to describe neurons that, when active, will “turn on” some recognizable, coordinated behavior. The overall organization of rhythmic motor systems can be represented as a series of “black boxes” representing the command and CPG function (Fig. 1) (Grillner, 1977). In this scheme, initiating stimuli would activate an appropriate command neuron or set of command neurons that in turn would activate the central pattern generator for a particular rhythmic behavior.
KeywordsCentral Pattern Generator Command Neuron Spike Frequency Adaptation Burst Pattern Ramp Current
Unable to display preview. Download preview PDF.
- Adams, P. R., Brown, D. A., and Constanti, A., 1982, M-currents and other potassium currents in bullfrog sympathetic neurons, J. Phyiol. (London) 330:537–572.Google Scholar
- Byrne, J. H., 1980a, Analysis of ionic conductance mechanisms in motor cells mediating inking behavior in Aplysia californica, J. Neurophysiol. 43:630–650.Google Scholar
- Connor, J. A., and Stevens, C. F., 1971, Voltage clamp studies of a transient outward current in gastropod neural somata, J. Physiol. (London) 213:21–30.Google Scholar
- Davis, W. J., 1976, Organizational concepts in the central motor networks of invertebrates, in: Neural Control of Locomotion (R. M. Herman, S. Grillner, P. S. G. Stein, and D. G. Stuart, eds.), Plenum Publishing Corporation, New York, pp. 265–292.Google Scholar
- Dekin, M. S., and Getting, P.A., 1983, Delayed excitation in neurons of the nucleus tractus solitarius studied in vitro, Neurosci. Abstr. 9:677.Google Scholar
- Getting, P. A., 1981, Mechanisms of pattern generation underlying swimming in Tritonia, I. Neuronal network formed by monosynaptic connections, J. Neuroophysiol. 46:65–79.Google Scholar
- Getting, P. A., 1983c, Neural control of swimming in Tritonia, in: Neural Origin of Rhythmic Movements (A. Roberts and B. L. Roberts, eds.), Cambridge University Press, Cambridge, England, pp. 89–128.Google Scholar
- Getting, P. A., and Dekin, M. S., 1983, Maintenance of Tritonia swimming by reciprocal excitation, Neurosci. Abstr. 9:541.Google Scholar
- Getting, P. A., and Dekin, M. S., 1985, Mechanisms of pattern generation underlying swimming in Tritonia, IV. Gating of a central pattern generator, J. Neurophysiol. (in press).Google Scholar
- Grillner, S., 1977, On the neural control of movement—A comparison of different rhythmic behaviors, in: Function and Formation of Neural Systems (G. S. Stent, ed.), Dahlem Konferenzen, Berlin, pp. 197–224.Google Scholar
- Heitler, W. J., and Mulloney, B., 1978, Crayfish motor neurons are an integral part of the swimmeret central oscillator, Soc. Neurosci. Abstr. 4:381.Google Scholar
- Weeks, J. C., and Kristan, W. B., Jr., 1978, Initiation, maintenance, and modulation of swimming in the medicinal leech by the activity of a single neurone, J. Exp. Biol. 77:71–88.Google Scholar