| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
* To whom correspondence should be addressed. E-mail: ken{at}biomed.queensu.ca.
A single spinal motoneuron receives tens of thousands of synapses. The neurotransmitters released by many of these synapses act on iontotropic receptors and alter the driving potential of neighbouring synapses. This interaction introduces an intrinsic non-linearity in motoneuron input-output properties where the response to two simultaneous inputs is less than the linear sum of the responses to each input alone. Our goal was to determine the impact of this non-linearity on the current delivered to the soma during activation of predetermined numbers and distributions of excitatory and inhibitory synapses. To accomplish this goal we constructed compartmental models constrained by detailed measurements of the geometry of the dendritic trees of three feline motoneurons. The current 'lost' due to local changes in driving potential was substantial and resulted in a highly non-linear relationship between the number of active synapses and the current reaching the soma. Background synaptic activity consisting of a balanced activation of excitatory and inhibitory synapses decreased the current delivered to the soma further, but reduced the non-linearity with respect to the total number of active excitatory synapses. Unexpectedly, simulations that mimicked experimental measures of non-linear summation, activation of two sets of excitatory synapses, resulted in nearly linear summation. This result suggests that non-linear summation can be difficult to detect, despite the substantial 'loss' of current due to non-linear summation. The magnitude of this 'loss' appears to limit motoneuron activity, based solely on activation of iontotropic receptors, to levels that are inadequate to generate functionally meaningful muscle forces.
This article has been cited by other articles:
|
|
 |
|
  C.J. Heckman, M. Johnson, C. Mottram, and J. Schuster Persistent Inward Currents in Spinal Motoneurons and Their Influence on Human Motoneuron Firing Patterns Neuroscientist, June 1, 2008; 14(3): 264 - 275. [Abstract] [PDF]
|
|
|
|
 |
|
 C. J. Heckman, A. S. Hyngstrom, and M. D. Johnson Active properties of motoneurone dendrites: diffuse descending neuromodulation, focused local inhibition J. Physiol., March 1, 2008; 586(5): 1225 - 1231. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Grande, T. V. Bui, and P. K. Rose Effect of localized innervation of the dendritic trees of feline motoneurons on the amplification of synaptic input: a computational study J. Physiol., September 1, 2007; 583(2): 611 - 630. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. T. Moritz, G. Newkirk, R. K. Powers, and M. D. Binder Facilitation of Somatic Calcium Channels Can Evoke Prolonged Tail Currents in Rat Hypoglossal Motoneurons J Neurophysiol, August 1, 2007; 98(2): 1042 - 1047. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. H. Schieber and G. Rivlis Partial Reconstruction of Muscle Activity From a Pruned Network of Diverse Motor Cortex Neurons J Neurophysiol, January 1, 2007; 97(1): 70 - 82. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M.-C. Perreault and M. Raastad Contribution of morphology and membrane resistance to integration of fast synaptic signals in two thalamic cell types J. Physiol., November 15, 2006; 577(1): 205 - 220. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
| Visit Other APS Journals Online |
