Key mechanisms for setting the input-output gain across the motoneuron pool.
This chapter summarizes a number of factors that control the "input-output" function across the motoneurons (MNs) comprising a single spinal motor nucleus. The main focus is on intrinsic properties of individual MNs that can be controlled by neuromodulators. These include: (1) amplification of the synaptic input at the cell's dendritic level by voltage-gated, persistent inward currents (plateau potentials); and (2) transduction of the net synaptic excitation into a frequency code (the MN's stimulus current-spike frequency relation) at the cell's soma/initial segment. Two other aspects of the synaptic control of MNs, which may affect their input-output gain, are also discussed. They include the hypotheses that: (1) a non-uniform distribution of synaptic effects to low- and high-threshold motor units causes a change in recruitment gain; and (2) recurrent inhibition, via motor axon collaterals and Renshaw cells, functions as a variable gain regulator of MN discharge.
Hultborn
Hans
H
Department of Medical Physiology, Panum Institute, University of Copenhagen, Copenhagen DK-2200, Denmark. h.hultborn@mfi.ku.dk
Brownstone
Robert B
RB
Toth
Tibor I
TI
Gossard
Jean-Pierre
JP
D000200:Action Potentials; D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D004525:Efferent Pathways / Q000502:physiology; D004553:Electric Conductivity; D009046:Motor Neurons / Q000502:physiology*; D011999:Recruitment, Neurophysiological; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology*; D013569:Synapses / Q000502:physiology