Chapter 5 Adapting Motoneurons for Motor Behavior

Publisher Summary Motor commands from the spinal cord to muscle fibers are coded as firing patterns in motor axons. Among all the patterns that motor axons can generate only a few ever occur. This chapter describes how the intrinsic properties of motoneurons are specialized and continuously fine-tuned to favor these useful patterns over all other impulse patterns. Motor behavior evolves on time scales of milliseconds and seconds. While rapid changes in activity are easily implemented by changes in synaptic excitation and inhibition of motoneurons, slower changes require increasing levels of processing from the premotor network. This computational burden is relieved by the intrinsic response properties and their regulation in motoneurons. The intrinsic response properties of motoneurons can adapt motoneurons to generate functionally useful output patterns. By the dynamic properties of L-type Ca ++ channels and their regulation by metabotropic receptors, the excitability of motoneurons and the time course of their responses can be regulated over a wide range. In addition, motor performance may be optimized and refined by supplementing ionotropic motor commands with the metabotropic regulation of recruitment order.

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