scholarly journals Inhibition linearizes firing rate responses in human motor units: implications for the role of persistent inward currents

2016 ◽  
Vol 595 (1) ◽  
pp. 179-191 ◽  
Author(s):  
Ann L. Revill ◽  
Andrew J. Fuglevand
Keyword(s):  
Firing Rate ◽  
Motor Units ◽  
Persistent Inward Currents ◽  
Inward Currents ◽  
Human Motor ◽  
Human Motor Units

Firing rate trajectories of human motor units during activity-dependent muscle potentiation

2021 ◽  
Author(s):  
Alexander M. Zero ◽  
Eric A. Kirk ◽  
Charles L. Rice
Keyword(s):  
Contractile Function ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Persistent Inward Currents ◽  
Motor Unit Firing ◽  
Inward Currents ◽  
Post Tetanic Potentiation ◽  
Human Motor ◽  
Activity Dependent ◽  
Human Motor Units

During activity-dependent potentiation (ADP) motor unit firing rates (MUFRs) are lower, however, the mechanism for this response is not known. During increasing torque isometric contractions at low contraction intensities, MUFR trajectories initially accelerate and saturate demonstrating a non-linear response due to the activation of persistent inward currents (PICs) at the motoneuron. The purpose was to assess whether PICs are a factor in the reduction of MUFRs during ADP. To assess this, MUFR trajectories were fit with competing functions of linear regression and a rising exponential (i.e., acceleration and saturation). Using fine-wire electrodes, discrete MU potential trains were recorded in the tibialis anterior during slowly increasing dorsiflexion contractions to 10% of maximal voluntary contraction following both voluntary (post-activation potentiation; PAP) and evoked (post-tetanic potentiation; PTP) contractions. In 8 participants, 25 MUs were recorded across both ADP conditions and compared to the control with no ADP effect. During PAP and PTP, the average MUFRs were 16.4% and 9.2% lower (both P≤ 0.001), respectively. More MUFR trajectories were better fit to the rising exponential during control (16/25) compared to PAP (4/25, P<0.001) and PTP (8/25, P=0.03). The MU samples that had a rising exponential MUFR trajectory during PAP and PTP displayed an ~11% lower initial acceleration compared to control (P<0.05). Thus, synaptic amplification and MUFR saturation due to PIC properties are attenuated during ADP regardless of the type of conditioning contraction. This response may contribute to lower MUFRs and likely occurred because synaptic input is reduced when contractile function is enhanced.

scholarly journals Estimation of the Contribution of Intrinsic Currents to Motoneuron Firing Based on Paired Motoneuron Discharge Records in the Decerebrate Cat

2008 ◽  
Vol 100 (1) ◽  
pp. 292-303 ◽  
Author(s):  
Randall K. Powers ◽  
Paul Nardelli ◽  
T. C. Cope
Keyword(s):  
Firing Rate ◽  
Motor Units ◽  
Unit Discharge ◽  
Decerebrate Cat ◽  
Persistent Inward Currents ◽  
Quantitative Estimates ◽  
Number Of Factors ◽  
Inward Currents ◽  
The Difference ◽  
Synaptic Drive

Motoneuron activation is strongly influenced by persistent inward currents (PICs) flowing through voltage-sensitive channels. PIC characteristics and their contribution to the control of motoneuron firing rate have been extensively described in reduced animal preparations, but their contribution to rate modulation in human motoneurons is controversial. It has recently been proposed that the analysis of discharge records of a simultaneously recorded pair of motor units can be used to make quantitative estimates of the PIC contribution, based on the assumption that the firing rate of an early recruited (reporter) unit can be used as a measure of the synaptic drive to a later recruited (test) unit. If the test unit's discharge is augmented by PICs, less synaptic drive will be required to sustain discharge than required to initially recruit it, and the difference in reporter unit discharge (Δ F) at test recruitment and de-recruitment is a measure of the size of the PIC contribution. We applied this analysis to discharge records of pairs of motoneurons in the decerebrate cat preparation, in which motoneuron PICs have been well-characterized and are known to be prominent. Mean Δ F values were positive in 58/63 pairs, and were significantly greater than zero in 40/63 pairs, as would be expected based on PIC characteristics recorded in this preparation. However, several lines of evidence suggest that the Δ F value obtained in a particular motoneuron pair may depend on a number of factors other than the PIC contribution to firing rate.

Properties of human motor units after prolonged activity at a constant firing rate

2003 ◽  
Vol 154 (4) ◽  
pp. 479-487 ◽  
Author(s):  
K. V. B. Johnson ◽  
S. C. Edwards ◽  
C. Van Tongeren ◽  
P. Bawa
Keyword(s):  
Firing Rate ◽  
Motor Units ◽  
Human Motor ◽  
Human Motor Units

scholarly journals Effects of joint immobilization on firing rate modulation of human motor units

2001 ◽  
Vol 530 (3) ◽  
pp. 507-519 ◽  
Author(s):  
Kazuhiko Seki ◽  
Yuko Taniguchi ◽  
Mitsuo Narusawa
Keyword(s):  
Firing Rate ◽  
Motor Units ◽  
Rate Modulation ◽  
Human Motor ◽  
Human Motor Units

scholarly journals Estimation of self-sustained activity produced by persistent inward currents using firing rate profiles of multiple motor units in humans

2020 ◽  
Vol 124 (1) ◽  
pp. 63-85 ◽  
Author(s):  
Babak Afsharipour ◽  
Nagib Manzur ◽  
Jennifer Duchcherer ◽  
Keith F. Fenrich ◽  
Christopher K. Thompson ◽  
...  
Keyword(s):  
Firing Rate ◽  
Motor Units ◽  
New Method ◽  
Persistent Inward Currents ◽  
Sustained Activity ◽  
Inward Currents ◽  
Synaptic Drive

A new method of estimating synaptic drive to multiple, simultaneously recorded motor units provides evidence that the portion of the depolarizing drive from persistent inward currents that contributes to self-sustained firing is similar across motoneurons of different sizes.

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