scholarly journals Distribution of the forces produced by motor unit activity in the human flexor digitorum profundus

2002 ◽  
Vol 543 (1) ◽  
pp. 289-296 ◽  
Author(s):  
S. L. Kilbreath ◽  
R. B. Gorman ◽  
J. Raymond ◽  
S. C. Gandevia
Keyword(s):  
Motor Unit ◽  
Unit Activity ◽  
Flexor Digitorum Profundus ◽  
Motor Unit Activity ◽  
Flexor Digitorum

Blockade of 5-HT2 receptors suppresses rate of torque development and motor unit discharge rate during rapid contractions

2021 ◽  
Author(s):  
Benjamin Ian Goodlich ◽  
Sean A Horan ◽  
Justin J Kavanagh
Keyword(s):  
Motor Unit ◽  
Unit Activity ◽  
Repeated Measures ◽  
Discharge Rate ◽  
Voluntary Contraction ◽  
Unit Discharge ◽  
Motor Unit Activity ◽  
Rate Of Torque Development ◽  
Motor Unit Discharge ◽  
Torque Development

Serotonin (5-HT) is a neuromodulator that is critical for regulating the excitability of spinal motoneurons and the generation of muscle torque. However, the role of 5-HT in modulating human motor unit activity during rapid contractions has yet to be assessed. Nine healthy participants (23.7 ± 2.2 yr) ingested 8 mg of the competitive 5-HT2 antagonist cyproheptadine in a double-blinded, placebo-controlled, repeated-measures experiment. Rapid dorsiflexion contractions were performed at 30%, 50% and 70% of maximal voluntary contraction (MVC), where motor unit activity was assessed by high-density surface electromyographic decomposition. A second protocol was performed where a sustained, fatigue-inducing dorsiflexion contraction was completed prior to undertaking the same 30%, 50% and 70% MVC rapid contractions and motor unit analysis. Motor unit discharge rate (p < 0.001) and rate of torque development (RTD; p = 0.019) for the unfatigued muscle were both significantly lower for the cyproheptadine condition. Following the fatigue inducing contraction, cyproheptadine reduced motor unit discharge rate (p < 0.001) and RTD (p = 0.024), where the effects of cyproheptadine on motor unit discharge rate and RTD increased with increasing contraction intensity. Overall, these results support the viewpoint that serotonergic effects in the central nervous system occur fast enough to regulate motor unit discharge rate during rapid powerful contractions.

scholarly journals An Analysis or the single Motor Unit Activity Involved in Oro-facial Functions

1986 ◽  
Vol 4 ◽  
pp. 115-122
Author(s):  
Hideho Handa ◽  
Yukihiro Fujita ◽  
Yasuyo Nomora ◽  
Hiroshi Suzuki ◽  
Kazuo Toda ◽  
...  
Keyword(s):  
Motor Unit ◽  
Unit Activity ◽  
Single Motor Unit ◽  
Single Motor ◽  
Motor Unit Activity

scholarly journals Myokymia and impaired muscular relaxation with continuous motor unit activity.

1979 ◽  
Vol 42 (6) ◽  
pp. 557-562 ◽  
Author(s):  
F D Lublin ◽  
P Tsairis ◽  
L J Streletz ◽  
R A Chambers ◽  
W F Riker ◽  
...  
Keyword(s):  
Motor Unit ◽  
Unit Activity ◽  
Muscular Relaxation ◽  
Motor Unit Activity ◽  
Continuous Motor Unit Activity

Effect of hypoxia on abdominal motor unit activities in spontaneously breathing cats

1996 ◽  
Vol 81 (6) ◽  
pp. 2428-2435 ◽  
Author(s):  
J. H. Mateika ◽  
E. Essif ◽  
R. F. Fregosi
Keyword(s):  
Motor Unit ◽  
Unit Activity ◽  
Motor Units ◽  
Discharge Frequency ◽  
Oblique Muscle ◽  
Single Motor Unit ◽  
Motor Unit Activity ◽  
Rate Coding ◽  
External Oblique ◽  
Spontaneously Breathing

Mateika, J. H., E. Essif, and R. F. Fregosi. Effect of hypoxia on abdominal motor unit activities in spontaneously breathing cats. J. Appl. Physiol. 81(6): 2428–2435, 1996.—These experiments were designed to examine the behavior of external oblique motor units in spontaneously breathing cats during hypoxia and to estimate the contribution of recruitment and rate coding to changes in the integrated external oblique electromyogram (iEMG). Motor unit activities in the external oblique muscle were identified while the cats expired against a positive end-expiratory pressure (PEEP) of 1–2.5 cmH2O. After localization of unit activity, PEEP was removed, and recordings were made continuously for 3–4 min during hyperoxia, normoxia, and hypoxia. A total of 35 single motor unit activities were recorded from 10 cats. At each level of fractional concentration of end-tidal O2, the motor unit activity was characterized by an abrupt increase in mean discharge frequency, at ∼30% of expiratory time, which then continued to increase gradually or remained constant before declining abruptly at the end of expiration. The transition from hyperoxia to normoxia and hypoxia was accompanied by an increase in the number of active motor units (16 of 35, 20 of 35, and 29 of 35, respectively) and by an increase in the mean discharge frequency of those units active during hyperoxia. The changes in motor unit activity recorded during hypoxia were accompanied by a significant increase in the average peak amplitude of the abdominal iEMG. Linear regression analysis revealed that motor unit rate coding was responsible for close to 60% of the increase in peak iEMG amplitude. The changes in abdominal motor unit activity and the external oblique iEMG that occurred during hypoxia were abolished if the arterial [Formula: see text] was allowed to fall. We conclude that external oblique motor units are activated during the latter two-thirds of expiration and that rate coding and recruitment contribute almost equally to the increase in expiratory muscle activity that occurs with hypoxia. In addition, the excitation of abdominal motor units during hypoxia is critically dependent on changes in CO2 and/or tidal volume.

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