Motoneurons are unique in being the only neurons in the CNS whose firing patterns can be easily recorded in human subjects. It has long been appreciated that the connection of motoneurons to their muscle fibers allows their action potentials to be amplified and recorded, but only recently has it become possible to simultaneously record the firing pattern of many motoneurons via array electrodes placed on the skin. These multiple firing patterns contain detailed information about the synaptic organization of motor commands to the motoneurons. This review focuses on parameters in these firing patterns that are directly linked to specific features of this organization. It is now well established that motor commands consist of three components, excitation, inhibition and neuromodulation; the importance of the third component has become increasing evident. Firing parameters linked to each of the three components are discussed, along with consideration of their limitations. Future work based on realistic computer simulations of motoneurons may allow quantitative "reverse engineering" of human motoneuron firing patterns to provide good estimates of the relative amplitudes and temporal patterns of all three components of motor commands.
- motor unit
- electrode array
- Copyright © 2017, Journal of Neurophysiology