Relative strengths and distributions of different sources of synaptic input to the motoneurone pool: implications for motor unit recruitment.

Understanding how synaptic inputs from segmental and descending systems shape motor output from the spinal cord requires information on the relative magnitudes of the synaptic currents produced by the different systems and their patterns of distribution within a motoneurone pool. Equally important are quantitative descriptions of how different synaptic inputs are integrated when they are concurrently active and of how voltage- and ligand-gated conductances on the dendrites of motoneurones affect the transfer of synaptic currents to the soma. We have carried out a number of experimental studies of these inter-related problems on motoneurones in the cat spinal cord and have explored the implications of our findings with computer simulations utilizing a synthetic model of the cat medial gastrocnemius motoneurone pool. This paper provides a brief review of the principal results of our studies.