A model of the feline medial gastrocnemius motoneuron-muscle system subjected to recurrent inhibition.
Recurrent inhibition in the mammalian spinal cord is complex, and its functions are not yet well understood. Skeletomotoneurons (alpha-MNs) excite, via recurrent axon collaterals, inhibitory Renshaw cells (RCs), which in turn inhibit alpha-MNs and other neurons. The anatomical and functional structure of the recurrent inhibitory network is nonhomogeneous, and the gain and filtering characteristics of RCs are modulated by inputs circumventing alpha-MNs. This complex organization is likely to play important roles for the discharge and recruitment properties of alpha-MNs. Modeling this system is a way of investigating hypothesized roles for normal functioning including muscle fatigue and different forms of physiological pathological tremor. In this paper, a detailed model including alpha-MNs, RCs, and the muscle fibers innervated by the alpha-MNs is presented. Outlines of the experimental data underlying the model and the modeling philosophy and procedure are presented. Then the behavior of a RC model is compared with experimental data reported in the literature. Model and experimental data agree well for burst responses elicited by synchronous single-pulse activation of different numbers of motor axons. In addition, the static relation between motor-axon activation rate and RC firing rate agree fairly well in model and experiment, and the same applies to the dynamic responses to step changes in motor-axon rate. The ultimate objective is to use this model in probing the role of recurrent inhibition in the control and stability of (isometric) muscular force under normal and altered conditions occurring during fatigue and muscle pain.
Uchiyama
Takanori
T
Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology, Keio University, 3-14-1, Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan. uchiyama@appi.keio.ac.jp
Johansson
Håkan
H
Windhorst
Uwe
U
D000818:Animals; D001676:Biofeedback, Psychology; D002415:Cats; D004558:Electric Stimulation; D007395:Interneurons / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008959:Models, Neurological; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D009716:Numerical Analysis, Computer-Assisted; D011930:Reaction Time; D011999:Recruitment, Neurophysiological; D013997:Time Factors