| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
The Journal of Neurophysiology Vol. 87 No. 4 April 2002, pp. 1850-1858
Copyright ©2002 by the American Physiological Society
1Division of Neuroscience and 2Department of Physical Therapy, Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
Gorassini, Monica,
Jaynie F. Yang,
Merek Siu, and
David J. Bennett.
Intrinsic Activation of Human Motoneurons: Possible Contribution
to Motor Unit Excitation. J. Neurophysiol. 87: 1850-1858, 2002. The main purpose of this study was to
estimate the contribution of intrinsic activation of human motoneurons
(e.g., by plateau potentials) during voluntary and reflexive muscle
contractions. Pairs of motor units were recorded from either the
tibialis anterior or soleus muscle during three different conditions:
1) during a brief muscle vibration followed by a slow
relaxation of a steady isometric contraction; 2) during a
triangular isometric torque contraction; and 3) during
passive sinusoidal muscle stretch superimposed on a steady isometric
contraction. In each case, the firing rate of a tonically firing
control motor unit was used as a measure of the effective
synaptic excitation (i.e., synaptic drive) to a slightly
higher-threshold test motor unit that was recruited and
de-recruited during a contraction trial. The firing rate of the control
unit was compared at recruitment and de-recruitment of the test unit.
This was done to determine whether the estimated synaptic drive needed
to recruit a motor unit was less than the amount needed to sustain
firing as a result of an added depolarization produced from intrinsic
sources. After test unit recruitment, the firing rate of the control
unit could be decreased significantly (on average by 3.6 Hz from an
initial recruitment rate of 9.8 Hz) before the test unit was
de-recruited during a descending synaptic drive. Similar decreases in
control unit rate occurred in all three experimental conditions. This
represents a possible 40% reduction in the estimated synaptic drive
needed to maintain firing of a motor unit compared with the estimated
amount needed to recruit the unit initially. The firing rates of both
the control and test units were modulated together in a highly parallel
fashion, suggesting that the unit pairs were driven by common synaptic inputs. This tight correlation further validated the use of the control
unit firing rate as a monitor of synaptic drive to the test motor unit.
The estimates of intrinsically mediated depolarization of human
motoneurons (
40% during moderate contractions) are consistent with
values obtained for plateau potentials obtained from intracellular recordings of motoneurons in reduced animal preparations, although various alternative mechanisms are discussed. This suggests that similar intrinsic conductances provide a substantial activation of
human motoneurons during moderate physiological activity.
This article has been cited by other articles:
|
|
 |
|
  R. K. Powers, P. Nardelli, and T. C. Cope Estimation of the Contribution of Intrinsic Currents to Motoneuron Firing Based on Paired Motoneuron Discharge Records in the Decerebrate Cat J Neurophysiol, July 1, 2008; 100(1): 292 - 303. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 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]
|
|
|
|
 |
|
 J. A. Norton, D. J. Bennett, M. E. Knash, K. C. Murray, and M. A. Gorassini Changes in sensory-evoked synaptic activation of motoneurons after spinal cord injury in man Brain, June 1, 2008; 131(6): 1478 - 1491. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Z. A. Riley, A. H. Maerz, J. C. Litsey, and R. M. Enoka Motor unit recruitment in human biceps brachii during sustained voluntary contractions J. Physiol., April 15, 2008; 586(8): 2183 - 2193. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. M. ElBasiouny and V. K. Mushahwar Suppressing the excitability of spinal motoneurons by extracellularly applied electrical fields: insights from computer simulations J Appl Physiol, November 1, 2007; 103(5): 1824 - 1836. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. C. Dean, L. M. Yates, and D. F. Collins Turning on the central contribution to contractions evoked by neuromuscular electrical stimulation J Appl Physiol, July 1, 2007; 103(1): 170 - 176. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
X. Li and D. J. Bennett Apamin-Sensitive Calcium-Activated Potassium Currents (SK) Are Activated by Persistent Calcium Currents in Rat Motoneurons J Neurophysiol, May 1, 2007; 97(5): 3314 - 3330. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. J. Harvey, X. Li, Y. Li, and D. J. Bennett 5-HT2 Receptor Activation Facilitates a Persistent Sodium Current and Repetitive Firing in Spinal Motoneurons of Rats With and Without Chronic Spinal Cord Injury J Neurophysiol, September 1, 2006; 96(3): 1158 - 1170. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. R. L. Baldwin, P. M. Klakowicz, and D. F. Collins Wide-pulse-width, high-frequency neuromuscular stimulation: implications for functional electrical stimulation J Appl Physiol, July 1, 2006; 101(1): 228 - 240. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. C. Button, K. Gardiner, T. Marqueste, and P. F. Gardiner Frequency-current relationships of rat hindlimb {alpha}-motoneurones J. Physiol., June 15, 2006; 573(3): 663 - 677. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. J. Fuglevand, A. P. Dutoit, R. K. Johns, and D. A. Keen Evaluation of plateau-potential-mediated 'warm up' in human motor units J. Physiol., March 15, 2006; 571(3): 683 - 693. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. M. ElBasiouny, D. J. Bennett, and V. K. Mushahwar Simulation of Ca2+ persistent inward currents in spinal motoneurones: mode of activation and integration of synaptic inputs J. Physiol., January 15, 2006; 570(2): 355 - 374. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. K. Floeter, P. Zhai, R. Saigal, Y. Kim, and J. Statland Motor Neuron Firing Dysfunction in Spastic Patients With Primary Lateral Sclerosis J Neurophysiol, August 1, 2005; 94(2): 919 - 927. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Li, X. Li, P. J. Harvey, and D. J. Bennett Effects of Baclofen on Spinal Reflexes and Persistent Inward Currents in Motoneurons of Chronic Spinal Rats With Spasticity J Neurophysiol, November 1, 2004; 92(5): 2694 - 2703. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. A. Gorassini, M. E. Knash, P. J. Harvey, D. J. Bennett, and J. F. Yang Role of motoneurons in the generation of muscle spasms after spinal cord injury Brain, October 1, 2004; 127(10): 2247 - 2258. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Nickolls, D. F. Collins, R. B. Gorman, D. Burke, and S. C. Gandevia Forces consistent with plateau-like behaviour of spinal neurons evoked in patients with spinal cord injuries Brain, March 1, 2004; 127(3): 660 - 670. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Li, M. A. Gorassini, and D. J. Bennett Role of Persistent Sodium and Calcium Currents in Motoneuron Firing and Spasticity in Chronic Spinal Rats J Neurophysiol, February 1, 2004; 91(2): 767 - 783. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. Taylor and R. M. Enoka Quantification of the Factors That Influence Discharge Correlation in Model Motor Neurons J Neurophysiol, February 1, 2004; 91(2): 796 - 814. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. D. Schmit, T. G. Hornby, V. M. Tysseling-Mattiace, and E. N. Benz Absence of Local Sign Withdrawal in Chronic Human Spinal Cord Injury J Neurophysiol, November 1, 2003; 90(5): 3232 - 3241. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Nozaki, N. Kawashima, Y. Aramaki, M. Akai, K. Nakazawa, Y. Nakajima, and H. Yano Sustained Muscle Contractions Maintained by Autonomous Neuronal Activity Within the Human Spinal Cord J Neurophysiol, October 1, 2003; 90(4): 2090 - 2097. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Zijdewind and C. K. Thomas Motor Unit Firing During and After Voluntary Contractions of Human Thenar Muscles Weakened by Spinal Cord Injury J Neurophysiol, April 1, 2003; 89(4): 2065 - 2071. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. H. Lee, J. J. Kuo, M. C. Jiang, and C. J. Heckman Influence of Active Dendritic Currents on Input-Output Processing in Spinal Motoneurons In Vivo J Neurophysiol, January 1, 2003; 89(1): 27 - 39. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Gorassini, J. F. Yang, M. Siu, and D. J. Bennett Intrinsic Activation of Human Motoneurons: Reduction of Motor Unit Recruitment Thresholds by Repeated Contractions J Neurophysiol, April 1, 2002; 87(4): 1859 - 1866. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
