Reciprocal and coactivation commands at the level of individual motor units in an extrinsic finger flexor–extensor muscle pair

2021 ◽  
Author(s):  
Shirin Madarshahian ◽  
Mark L. Latash
Keyword(s):  
Motor Units ◽  
Extensor Muscle ◽  
Muscle Pair ◽  
Individual Motor

Summation of motor unit tensions in the tibialis posterior muscle of the cat under isometric and nonisometric conditions

1991 ◽  
Vol 66 (6) ◽  
pp. 1838-1846 ◽  
Author(s):  
R. K. Powers ◽  
M. D. Binder
Keyword(s):  
Motor Unit ◽  
Muscle Fibers ◽  
Stimulus Frequency ◽  
Muscle Length ◽  
Motor Units ◽  
Force Transducer ◽  
Tibialis Posterior ◽  
Single Motor Units ◽  
Individual Motor ◽  
Stimulation Of

1. The tension produced by the combined stimulation of two to four single motor units of the cat tibialis posterior muscle was compared with the algebraic sum of the tensions produced by each individual motor unit. Comparisons were made under isometric conditions and during imposed changes in muscle length. 2. Under isometric conditions, the tension resulting from combined stimulation of units displayed marked nonlinear summation, as previously reported in other cat hindlimb muscles. On average, the measured tension was approximately 20% greater than the algebraic sum of the individual unit tensions. However, small trapezoidal movements imposed on the muscle during stimulation significantly reduced the degree of nonlinear summation both during and after the movement. This effect was seen with imposed movements as small as 50 microns. 3. The degree of nonlinear summation was not dependent on motor unit size or on stimulus frequency. The effect was also unrelated to tendon compliance because the degree of nonlinear summation of motor unit forces was unaffected by the inclusion of different amounts of the external tendon between the muscle and the force transducer. 4. Our results support previous suggestions that the force measured when individual motor units are stimulated under isometric conditions is reduced by friction between the active muscle fibers and adjacent passive fibers. These frictional effects are likely to originate in the connective tissue matrix connecting adjacent muscle fibers. However, because these effects are virtually eliminated by small movements, linear summation of motor unit tensions should occur at low force levels under nonisometric conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-lasting excitability changes of soleus alpha-motoneuron induced by midpontine stimulation in decerebrate, standing cat

1986 ◽  
Vol 55 (3) ◽  
pp. 449-468 ◽  
Author(s):  
T. Sakamoto ◽  
Y. Atsuta ◽  
S. Mori
Keyword(s):  
Muscle Tone ◽  
Motor Units ◽  
Input Resistance ◽  
Extensor Muscle ◽  
Membrane Excitability ◽  
Peak Voltage ◽  
Resistance Change ◽  
Time To Peak ◽  
Dorsal Portion ◽  
Force Reduction

Stimulation of the dorsal portion of the caudal tegmental field (DTF) in the pons resulted in hyperpolarization of extensor alpha-motoneurons (alpha-MNs) that persisted for several minutes after cessation of the stimulation. The resulting inhibition of alpha-MN discharge led to a progressive reduction in the number of active motor units. Renshaw cells, persistently active at high levels of extensor muscle tone, were abruptly silenced by DTF stimulation. Active discharge was renewed at the time of cessation of the stimulation but at a frequency reduced in proportion to the persistently lowered level of extensor muscle tone. Ia primary afferents were tonically active during the high extensor tonus of reflex standing. DTF stimulation was accompanied by a brief, slight increase in Ia discharge frequency followed by a reduction in frequency variably correlated to the magnitude of extensor force reduction. Orthodromically elicited Ia EPSPs in the soleus alpha-MNs were reduced in peak voltage, time to peak, and half width during the hyperpolarization accompanying DTF stimulation. All of these parameters recovered beyond their prestimulus values with the cessation of DTF stimulation in spite of the persisting hyperpolarization. Antidromically initiated invasion of the somatodendritic (SD) segment of the motoneuron membrane was delayed and sometimes blocked during DTF stimulation. At the same time, the peak voltage of the SD action potential was reduced. There was an immediate recovery of these changes on termination of DTF stimulation, although the poststimulus hyperpolarization persisted. Intracellular injection of depolarizing current steps during DTF stimulation revealed a depression of membrane excitability that persisted during the hyperpolarization that followed the termination of the DTF stimulation. Depolarizing and hyperpolarizing steps of intracellular current were used to demonstrate a reduction of cellular input resistance during DTF stimulation. The resistance values rapidly returned to prestimulus levels following the cessation of DTF stimulation. It was demonstrated that the degree of resistance change is greater and that the magnitude of DTF-induced hyperpolarization is smaller for low-resistance cells than for high-resistance cells. Iontophoretically induced increase in intracellular Cl- resulted in a reversal of both Ia IPSPs and the hyperpolarization induced by DTF stimulation. The hyperpolarization enduring after DTF stimulation was not affected by the Cl- injection.

scholarly journals The innervation and organization of motor units in a series-fibered human muscle: the brachioradialis

2010 ◽  
Vol 108 (6) ◽  
pp. 1530-1541 ◽  
Author(s):  
Zoia C. Lateva ◽  
Kevin C. McGill ◽  
M. Elise Johanson
Keyword(s):  
Human Subjects ◽  
Standing Waves ◽  
Motor Units ◽  
Human Muscle ◽  
Motor Unit Action Potential ◽  
Distal Muscle ◽  
Normal Human ◽  
Motor Unit Action ◽  
Unit Action ◽  
Individual Motor

We studied the innervation and organization of motor units in the brachioradialis muscle of 25 normal human subjects. We recorded intramuscular EMG signals at points separated by 15 mm along the proximodistal muscle axis during moderate isometric contractions, identified from 27 to 61 (mean 39) individual motor units per subject using EMG decomposition, and estimated the locations of the endplates and distal muscle/tendon junctions from the motor-unit action potential (MUAP) propagation patterns and terminal standing waves. In three subjects all the motor units were innervated in a single endplate zone. In the other 22 subjects, the motor units were innervated in 3–6 (mean 4) distinct endplate zones separated by 15–55 mm along the proximodistal axis. One-third of the motor units had fibers innervated in more than one zone. The more distally innervated motor units had distinct terminal waves indicating tendonous termination, while the more proximal motor units lacked terminal waves, indicating intrafascicular termination. Analysis of blocked MUAP components revealed that 19% of the motor units had at least one doubly innervated fiber, i.e., a fiber innervated in two different endplate zones by two different motoneurons, and thus belonging to two different motor units. These results are consistent with the brachioradialis muscle having a series-fibered architecture consisting of multiple, overlapping bands of muscle fibers in most individuals and a simple parallel-fibered architecture in some individuals.

Anatomic and physiological characteristics of the ferret lateral rectus muscle and abducens nucleus

2007 ◽  
Vol 103 (5) ◽  
pp. 1706-1714 ◽  
Author(s):  
Keith N. Bishop ◽  
J. Ross McClung ◽  
Stephen J. Goldberg ◽  
Mary S. Shall
Keyword(s):  
Motor Units ◽  
Lateral Rectus ◽  
Contraction Time ◽  
Fatigue Index ◽  
Muscle Twitch ◽  
Abducens Nucleus ◽  
Single Motor Unit ◽  
Twitch Contraction ◽  
Whole Muscle ◽  
Individual Motor

The ferret has become a popular model for physiological and neurodevelopmental research in the visual system. We believed it important, therefore, to study extraocular whole muscle as well as single motor unit physiology in the ferret. Using extracellular stimulation, 62 individual motor units in the ferret abducens nucleus were evaluated for their contractile characteristics. Of these motor units, 56 innervated the lateral rectus (LR) muscle alone, while 6 were split between the LR and retractor bulbi (RB) muscle slips. In addition to individual motor units, the whole LR muscle was evaluated for twitch, tetanic peak force, and fatigue. The abducens nucleus motor units showed a twitch contraction time of 15.4 ms, a mean twitch tension of 30.2 mg, and an average fusion frequency of 154 Hz. Single-unit fatigue index averaged 0.634. Whole muscle twitch contraction time was 16.7 ms with a mean twitch tension of 3.32 g. The average fatigue index of whole muscle was 0.408. The abducens nucleus was examined with horseradish peroxidase conjugated with the subunit B of cholera toxin histochemistry and found to contain an average of 183 motoneurons. Samples of LR were found to contain an average of 4,687 fibers, indicating an LR innervation ratio of 25.6:1. Compared with cat and squirrel monkeys, the ferret LR motor units contract more slowly yet more powerfully. The functional visual requirements of the ferret may explain these fundamental differences.

scholarly journals Bladder Muscle Biopsy and Urethral Sphincter EMG in Patients with Bladder Dysfunction after Pelvic Surgery

1986 ◽  
Vol 79 (5) ◽  
pp. 270-273 ◽  
Author(s):  
R S Kirby ◽  
C J Fowler ◽  
S A Gilpin J A Gosling ◽  
E J G Milroy ◽  
R T Turner-Warwick
Keyword(s):  
Peripheral Nerve ◽  
Muscle Biopsy ◽  
Peripheral Nerve Injury ◽  
Bladder Dysfunction ◽  
Effective Means ◽  
Motor Units ◽  
Pelvic Surgery ◽  
Urethral Sphincter ◽  
Sphincter Electromyography ◽  
Individual Motor

Eleven patients who suffered persistent bladder dysfunction after pelvic surgery have been investigated by needle urethral sphincter electromyography (EMG) and bladder muscle biopsy, and the results compared with those obtained in a series of controls. Individual motor units recorded from the urethral sphincter in patients who had undergone pelvic surgery were strikingly abnormal, suggesting the presence of reinnervation, and the density of detrusor innervation was significantly reduced. However, since reduction in the density of detrusor innervation may occur in circumstances other than peripheral nerve injury, we conclude that urethral sphincter EMG provides the most effective means of assessing damage to vesico-urethral innervation as a result of previous pelvic surgery.

Cross-reinnervated motor units in cat muscle. I. Flexor digitorum longus muscle units reinnervated by soleus motoneurons

1985 ◽  
Vol 54 (4) ◽  
pp. 818-836 ◽  
Author(s):  
R. P. Dum ◽  
M. J. O'Donovan ◽  
J. Toop ◽  
R. E. Burke
Keyword(s):  
Muscle Fibers ◽  
Motor Units ◽  
Muscle Fiber Types ◽  
Type I ◽  
Fiber Types ◽  
Glycogen Depletion ◽  
Flexor Digitorum Longus ◽  
Wet Weight ◽  
Flexor Digitorum ◽  
Individual Motor

The properties of flexor digitorum longus (FDL) muscles and of individual motor units were studied in cats 30-50 wk after self-reinnervation by FDL motoneurons (FDL----FDL) or cross-reinnervation by soleus (SOL) motoneurons (SOL----FDL). Individual motor units were functionally isolated by intracellular recording and stimulation of identified SOL alpha-motoneurons. Glycogen-depletion methods permitted histochemical study of muscle fibers belonging to physiologically characterized muscle units. The observations were compared with data from normal cat FDL muscles and motor units (27). Intentionally self-reinnervated FDL muscles (FDL----FDL; n = 5) were normal in size and wet weight. FDL----FDL motor units could be classified into the same physiological categories found in normal FDL [types: fast contracting, fatigable (FF), fast contracting, fatigue resistant (FR), and slow (S); n = 24], with approximately the same proportions as normal. The histochemical muscle fiber types associated with these categories were also qualitatively normal although there was evidence of marked distortion of the normal histochemical mosaic. These data confirm other studies of self-reinnervation and suggest that self-reinnervation can produce complete interconversion of muscle fiber types. Cross-reinnervation of FDL muscle by SOL motoneurons (SOL----FDL; n = 12) produced muscles that were smaller (about half the normal wet weight) and more red than normal. SOL----FDL muscle contracted more slowly than normal or FDL----FDL muscles and had much higher proportions of histochemical type I muscle fibers. In those SOL----FDL muscles, in which little or no unwanted self-reinnervation could be demonstrated, greater than 95% of the muscle fibers were type I. Forty-one individual motor units in SOL----FDL muscles were isolated by intracellular penetration in functionally identified SOL alpha-motoneurons. Their muscle units were all type S by physiological criteria (absence of "sag" in unfused tetani and marked resistance to fatigue). SOL----FDL muscle units had contraction times and fatigue properties that were essentially identical to those of type S units in the normal FDL. All of the seven units, successfully studied by glycogen depletion, exhibited histochemical type I fibers. SOL motoneurons that innervated FDL muscle units had slightly shorter afterhyperpolarization durations than normal SOL cells, but axonal conduction velocities were normal.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of single intracortical microstimuli in motor cortex on activity of identified forearm motor units in behaving monkeys

1985 ◽  
Vol 54 (5) ◽  
pp. 1194-1212 ◽  
Author(s):  
S. S. Palmer ◽  
E. E. Fetz
Keyword(s):  
Time Course ◽  
Single Pulse ◽  
Motor Units ◽  
Emg Activity ◽  
Base Line ◽  
Precentral Gyrus ◽  
Behaving Monkeys ◽  
A Site ◽  
Cumulative Sums ◽  
Individual Motor

We examined the magnitude and extent of output effects elicited from focal cortical sites on the activity of individual motor units (MUs) by delivering single-pulse intracortical microstimuli (S-ICMS) (5-15 microA) during isometric wrist activity. Stimulation sites in the precentral gyrus (area 4) were chosen for study if stimulus-triggered averages (stimulus-TAs) of multiunit electromyograms (EMGs) revealed poststimulus facilitation (PStimF) of EMG activity in any of the coactivated wrist muscles. Single MUs were then isolated in the facilitated muscles with a remotely controlled tripolar microelectrode. MUs were identified by their signatures in their parent muscles (from MU-triggered averages of EMGs) and by their firing pattern during ramp-and-hold wrist responses. One objective was to quantify the magnitude and time course of the effects on single MUs by compiling peristimulus histograms of MU firing. The cross-correlation histograms between S-ICMS and MU action potentials showed peaks with onset latencies of 8.8 +/- 1.7 ms (mean +/- SD, n = 64) and durations of 1.8 +/- 1.2 ms (n = 104). The cumulative sums of the correlogram peaks resembled the rising phase of corticomotoneuronal excitatory postsynaptic potentials previously recorded in forelimb motoneurons. Comparison of correlogram peaks with stimulus-TAs of MU potentials suggests that the duration of PStimF of multiunit EMG can be accounted for, in approximately equal proportions, by l) the variation in firing time of single MUs (i.e., the width of the MU correlogram peaks), 2) the width of single MU potentials, and 3) the contribution of different MUs at different latencies. The sizes of the correlogram peaks relative to base line were larger than the PStimF of multiunit EMGs, and increased more rapidly with stimulus intensity, indicating appreciable cancellation in the multiunit records. A second objective was to determine whether S-ICMS affected all the MUs of a facilitated muscle, or only a particular subset. Of 104 MUs sampled in facilitated muscles, 99 (95%) were found to be individually facilitated (P less than 0.05). MU firing patterns during isometric ramp-and-hold torque responses were characterized as phasic, phasic-tonic, tonic, or decrementing; stimulation at a given cortical site was found to facilitate all four types of MUs. When more than one muscle showed PStimF from a site, MUs belonging to each of the facilitated muscles were facilitated individually by S-ICMS at that site.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Does Strict Validation Criteria for Individual Motor Units Alter Extrapolation Analyses of the Motor Unit Pool?

2019 ◽  
Vol 51 (Supplement) ◽  
pp. 341-342
Author(s):  
Jesus A. Hernandez-Sarabia ◽  
Alejandra Barrera-Curiel ◽  
Ryan J. Colquhoun ◽  
Jason M. DeFreitas
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Validation Criteria ◽  
Individual Motor
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