Motor Unit Territories in the Human Perioral Musculature

1994 ◽  
Vol 37 (5) ◽  
pp. 975-984 ◽  
Author(s):  
Lisa Goffman ◽  
Anne Smith
Keyword(s):  
Motor Unit ◽  
Cross Correlation ◽  
Coherence Function ◽  
Broad Band ◽  
Motor Units ◽  
Oscillatory Activity ◽  
Frequency Range ◽  
Motor Tasks ◽  
Single Motor Unit ◽  
Lower Lip

The perioral region was divided into four quadrants, and electromyograms (EMGs) were recorded from each area. The coherence function (i.e., the squared cross correlation between two signals computed at each frequency in the spectrum) was used to determine aspects of the organization of motor unit territories and to examine potential higher level sources of input in speech and nonspeech tasks. Coherence functions were computed between pairs of EMGs and were examined for significant values in the range of 20–240 Hz. When two pairs of electrodes were intentionally placed to record the activity from a common subset of motor units in a single quadrant of the lower lip, all subjects exhibited significant broad-band coherence in every frequency in all experimental tasks. Thus, the presence of such a pattern of broad-band significant coherence for EMG pairs recorded from different quadrants would indicate that single motor unit territories extended across perioral quadrants. When separate EMG recordings were obtained from the four quadrants of the lips, coherence functions computed between EMG pairs were typically zero across the entire frequency range. These findings suggest that perioral motor unit territories are organized into nonoverlapping quadrants. Further, the present analyses suggest that, unlike bilateral pairs of jaw-closing muscles during chewing, these motor units are not driven by any correlated oscillatory activity in chewing or other oral motor tasks.

Recruitment Thresholds of Lower-Lip Motor Units with Changes in Movement Direction

1984 ◽  
Vol 27 (1) ◽  
pp. 6-12 ◽  
Author(s):  
Michael D. McClean
Keyword(s):  
Motor Unit ◽  
Functional Organization ◽  
Motor Units ◽  
Movement Direction ◽  
General Motor ◽  
Single Motor Unit ◽  
Lower Lip ◽  
Direction Of Movement ◽  
Lip Movement ◽  
Recruitment Order

Recruitment threshold may provide a useful measure for understanding the functional organization of speech muscles. The objective of the present study was to describe the recruitment thresholds of orbicularis oris inferior (OOI) and mentalis (MENT) motor units with changes in the direction of lower lip movement. Three subjects produced slow ramp displacements of the lower lip in three directions while simultaneous single motor unit recordings were obtained. Analysis was performed on 28 OOI units and 20 MENT units. The OOI motor units had their lowest recruitment thresholds for anterior lip movements, and the MENT units had their lowest thresholds for superior movements. In general, motor unit recruitment order was fixed and recruitment thresholds remained proportional with changes in the direction of movement. There was one instance of a recruitment order reversal in a pair of MENT motor units.

Rectification is required to extract oscillatory envelope modulation from surface electromyographic signals

2014 ◽  
Vol 112 (7) ◽  
pp. 1685-1691 ◽  
Author(s):  
Christopher J. Dakin ◽  
Brian H. Dalton ◽  
Billy L. Luu ◽  
Jean-Sébastien Blouin
Keyword(s):  
Motor Unit ◽  
Stimulus Frequency ◽  
Motor Units ◽  
Surface Emg ◽  
Medial Gastrocnemius ◽  
Single Motor Unit ◽  
Single Motor ◽  
Single Motor Units ◽  
Emg Signal ◽  
Envelope Modulation

Rectification of surface electromyographic (EMG) recordings prior to their correlation with other signals is a widely used form of preprocessing. Recently this practice has come into question, elevating the subject of EMG rectification to a topic of much debate. Proponents for rectifying suggest it accentuates the EMG spike timing information, whereas opponents indicate it is unnecessary and its nonlinear distortion of data is potentially destructive. Here we examine the necessity of rectification on the extraction of muscle responses, but for the first time using a known oscillatory input to the muscle in the form of electrical vestibular stimulation. Participants were exposed to sinusoidal vestibular stimuli while surface and intramuscular EMG were recorded from the left medial gastrocnemius. We compared the unrectified and rectified surface EMG to single motor units to determine which method best identified stimulus-EMG coherence and phase at the single-motor unit level. Surface EMG modulation at the stimulus frequency was obvious in the unrectified surface EMG. However, this modulation was not identified by the fast Fourier transform, and therefore stimulus coherence with the unrectified EMG signal failed to capture this covariance. Both the rectified surface EMG and single motor units displayed significant coherence over the entire stimulus bandwidth (1–20 Hz). Furthermore, the stimulus-phase relationship for the rectified EMG and motor units shared a moderate correlation ( r = 0.56). These data indicate that rectification of surface EMG is a necessary step to extract EMG envelope modulation due to motor unit entrainment to a known stimulus.

EMG Changes in Human Thenar Motor Units With Force Potentiation and Fatigue

2006 ◽  
Vol 95 (3) ◽  
pp. 1518-1526 ◽  
Author(s):  
C. K. Thomas ◽  
R. S. Johansson ◽  
B. Bigland-Ritchie
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Emg Activity ◽  
Single Motor Unit ◽  
Tetanic Force ◽  
Twitch Force ◽  
Emg Amplitude ◽  
Before And After ◽  
Induced Changes ◽  
Motor Unit Emg

Few studies have analyzed activity-induced changes in EMG activity in individual human motor units. We studied the changes in human thenar motor unit EMG that accompany the potentiation of twitch force and fatigue of tetanic force. Single motor unit EMG and force were recorded in healthy subjects in response to selective stimulation of their motor axons within the median nerve just above the elbow. Twitches were recorded before and after a series of pulse trains delivered at frequencies that varied between 5 and 100 Hz. This stimulation induced significant increases in EMG amplitude, duration, and area. However, in relative terms, all of these EMG changes were substantially smaller than the potentiation of twitch force. Another 2 min of stimulation (13 pulses at 40 Hz each second) induced additional potentiation of EMG amplitude, duration, and area, but the tetanic force from every unit declined. Thus activity-induced changes in human thenar motor unit EMG do not indicate the alterations in force or vice versa. These data suggest that different processes underlie the changes in EMG and force that occur during human thenar motor unit activity.

Maximal force as a function of anatomical features of motor units in the cat tibialis anterior

1987 ◽  
Vol 57 (6) ◽  
pp. 1730-1745 ◽  
Author(s):  
S. C. Bodine ◽  
R. R. Roy ◽  
E. Eldred ◽  
V. R. Edgerton
Keyword(s):  
Motor Unit ◽  
Tibialis Anterior ◽  
Periodic Acid ◽  
Muscle Fibers ◽  
Motor Units ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Periodic Acid Schiff ◽  
Cross Sectional ◽  
Single Motor Unit

In 11 tibialis anterior muscles of the cat, a single motor unit was characterized physiologically and subsequently depleted of its glycogen through repetitive stimulation of an isolated ventral root filament. Muscle cross sections were stained for glycogen using a periodic acid-Schiff reaction, and single-fiber optical densities were determined to identify those fibers belonging to the stimulated motor unit. Innervation ratios were determined by counting the total number of muscle fibers in a motor unit in sections taken through several levels of the muscle. The average innervation ratios for the fast, fatigueable (FF) and fast, fatigue-resistant (FR) units were similar. However, the slow units (S) contained 61% fewer fibers than the fast units (FF and FR). Muscle fibers belonging to S and FR units were similar in cross-sectional area, whereas fibers belonging to FF units were significantly larger than fibers belonging to either S or FR units. Additionally, muscle fibers innervated by a single motoneuron varied by two- to eightfold in cross-sectional area. Specific tensions, based on total cross-sectional area determined by summing the areas of all muscle fibers of each unit, showed a modest difference between fast and slow units, the means being 23.5 and 17.2 N X cm-2, respectively. Variations in maximum tension among units could be explained principally by innervation ratio, although fiber cross-sectional area and specific tension did contribute to differences between unit types.

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.

Vastus lateralis surface and single motor unit EMG following submaximal shortening and lengthening contractions

2008 ◽  
Vol 33 (6) ◽  
pp. 1086-1095 ◽  
Author(s):  
Teatske M. Altenburg ◽  
Cornelis J. de Ruiter ◽  
Peter W.L. Verdijk ◽  
Willem van Mechelen ◽  
Arnold de Haan
Keyword(s):  
Motor Unit ◽  
Muscle Activation ◽  
Discharge Rate ◽  
Vastus Lateralis ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Knee Extensors ◽  
Single Motor Unit ◽  
Discharge Rates ◽  
Active Motor

A single shortening contraction reduces the force capacity of muscle fibers, whereas force capacity is enhanced following lengthening. However, how motor unit recruitment and discharge rate (muscle activation) are adapted to such changes in force capacity during submaximal contractions remains unknown. Additionally, there is limited evidence for force enhancement in larger muscles. We therefore investigated lengthening- and shortening-induced changes in activation of the knee extensors. We hypothesized that when the same submaximal torque had to be generated following shortening, muscle activation had to be increased, whereas a lower activation would suffice to produce the same torque following lengthening. Muscle activation following shortening and lengthening (20° at 10°/s) was determined using rectified surface electromyography (rsEMG) in a 1st session (at 10% and 50% maximal voluntary contraction (MVC)) and additionally with EMG of 42 vastus lateralis motor units recorded in a 2nd session (at 4%–47%MVC). rsEMG and motor unit discharge rates following shortening and lengthening were normalized to isometric reference contractions. As expected, normalized rsEMG (1.15 ± 0.19) and discharge rate (1.11 ± 0.09) were higher following shortening (p < 0.05). Following lengthening, normalized rsEMG (0.91 ± 0.10) was, as expected, lower than 1.0 (p < 0.05), but normalized discharge rate (0.99 ± 0.08) was not (p > 0.05). Thus, muscle activation was increased to compensate for a reduced force capacity following shortening by increasing the discharge rate of the active motor units (rate coding). In contrast, following lengthening, rsEMG decreased while the discharge rates of active motor units remained similar, suggesting that derecruitment of units might have occurred.

scholarly journals Motor unit control and force fluctuation during fatigue

2009 ◽  
Vol 107 (1) ◽  
pp. 235-243 ◽  
Author(s):  
Paola Contessa ◽  
Alexander Adam ◽  
Carlo J. De Luca
Keyword(s):  
Motor Unit ◽  
Coefficient Of Variation ◽  
Cross Correlation ◽  
Motor Units ◽  
Vastus Lateralis Muscle ◽  
Force Output ◽  
Endurance Time ◽  
Firing Rates ◽  
Force Fluctuation ◽  
The Cross

During isometric contractions, the fluctuation of the force output of muscles increases as the muscle fatigues, and the contraction is sustained to exhaustion. We analyzed motor unit firing data from the vastus lateralis muscle to investigate which motor unit control parameters were associated with the increased force fluctuation. Subjects performed a sequence of isometric constant-force contractions sustained at 20% maximal force, each spaced by a 6-s rest period. The contractions were performed until the mean value of the force output could not be maintained at the desired level. Intramuscular EMG signals were detected with a quadrifilar fine-wire sensor. The EMG signals were decomposed to identify all of the firings of several motor units by using an artificial intelligence-based set of algorithms. We were able to follow the behavior of the same motor units as the endurance time progressed. The force output of the muscle was filtered to remove contributions from the tracking task. The coefficient of variation of the force was found to increase with endurance time ( P < 0.001, R2 = 0.51). We calculated the coefficient of variation of the firing rates, the synchronization of pairs of motor unit firings, the cross-correlation value of the firing rates of pairs of motor units, the cross-correlation of the firing rates of motor units and the force, and the number of motor units recruited during the contractions. Of these parameters, only the cross-correlation of the firing rates ( P < 0.01, R2 = 0.10) and the number of recruited motor units ( P = 0.042, R2 = 0.22) increased significantly with endurance time for grouped subjects. A significant increase ( P < 0.001, R2 = 0.16) in the cross-correlation of the firing rates and force was also observed. It is suggested that the increase in the cross-correlation of the firing rates is likely due to a decrease in the sensitivity of the proprioceptive feedback from the spindles.

The motor-unit population of the cat tenuissimus muscle

1988 ◽  
Vol 59 (4) ◽  
pp. 1128-1142 ◽  
Author(s):  
A. Lev-Tov ◽  
C. A. Pratt ◽  
R. E. Burke
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Retrograde Transport ◽  
Length Change ◽  
Single Type ◽  
Motor Nucleus ◽  
Single Motor Unit ◽  
Hindlimb Muscles ◽  
Typical Type ◽  
Fast Twitch

1. We studied the organization of motor units in the tenuissimus (TEN) muscle of pentobarbital-anesthetized cats. The cat TEN is a long, delicate straplike muscle that spans hip and knee, which has a very flat length-tension curve through 22 mm of length change. 2. The TEN motor nucleus, labeled by retrograde transport of several forms of horseradish peroxidase, was composed of 8-31 cells in different cats, of which about half were, on average, in the size range of alpha-motoneurons. TEN motoneurons were scattered through the ventrolateral portion of lamina IX, over a rostrocaudal distance of up to 6.5 mm, making it relatively easy to isolate individual TEN motor axons for single motor-unit stimulation. 3. Individual TEN muscle units were classified into four groups [fast-twitch, fatigable (FF), intermediate, fatigue-resistant (Fint), fast-twitch, fatigue-resistant (FR), and slow-twitch, fatigue resistant (S)] on the basis of "sag" and fatigue index mechanical properties, as in other cat hindlimb muscles. There was a relatively large proportion of Fint units (28%) in the TEN sample, and the range of tetanic tension (approximately 19-fold) was much smaller than found in other cat hindlimb muscles. 4. A majority of TEN muscle fibers could be classified into the three major histochemical types (IIB, IIA, and I) found in other cat muscles, but a substantial minority remained "unclassified." A single type Fint muscle unit was successfully depleted of glycogen for histochemical study. It exhibited a typical type IIB histochemical profile. 5. Despite its unusual morphology, the cat TEN contains the same types of motor units found in larger, more "typical" limb muscles.

Motor-unit responses in human wrist flexor and extensor muscles to transcranial cortical stimuli

1987 ◽  
Vol 58 (5) ◽  
pp. 1168-1185 ◽  
Author(s):  
B. Calancie ◽  
M. Nordin ◽  
U. Wallin ◽  
K. E. Hagbarth
Keyword(s):  
Motor Unit ◽  
Single Unit ◽  
Motor Units ◽  
Onset Latency ◽  
Size Principle ◽  
Single Motor Unit ◽  
Motor Responses ◽  
Wrist Flexor ◽  
Extensor Muscles ◽  
Single Unit Recordings

1. Transcranial cortical stimuli (TCCS) were used to elicit motor responses in contralateral wrist flexor and extensor muscles of healthy adult subjects. The motor responses were assessed by surface EMG recordings, by needle recordings of single motor-unit discharges, and by measurements of wrist twitch force. Our main aim was to analyze the single-unit events underlying those changes in latency, amplitude, and duration of the compound EMG responses, which could be induced by voluntary preactivation of target muscles and by changes in stimulation strength. 2. Different stimulus strengths were tested with and without background contractions in the flexor or extensor muscles. For each test (consisting of a series of 20 stimuli) the compound EMG responses were averaged and displayed together with the averaged wrist force signals. Responses of individual flexor and extensor motor units were displayed in raster diagrams and peristimulus time histograms. For units exhibiting a background firing, the mean background interdischarge interval was calculated and compared with the subsequent poststimulus intervals. 3. In relaxed muscles, a shortening of onset latency of evoked compound EMG responses was observed when raising stimulation strength. A similar latency reduction was not seen in any of the single-unit recordings. This would be consistent with the size principle of motoneuron recruitment. 4. A shortening of onset latency of evoked EMG potentials was observed also as a result of a voluntary preactivation. Such latency shifts, which were seen also in single-unit recordings, might be attributed to variations in the time required for D and I wave temporal summation at the anterior horn cell. 5. When raising stimulation strength or when adding voluntary background contraction, the evoked compound EMG potential grew not only in amplitude but also in duration, as later peaks of activity were added to the initial ones. Under optimal conditions (strong stimulus + background contraction), the period of excitation (termed E1) had an onset latency of approximately 15 ms and a duration of approximately 35 ms and was similar for wrist flexor and extensor muscles. 6. We never saw the same flexor or extensor unit fire more than once during the E1 period. For units preactivated by a background contraction, the stimulus-triggered impulse exhibited latency shifts, which, to a large extent, depended on the timing of the stimulus in relation to a preceding background discharge and which could be influenced by a change in stimulation strength.(ABSTRACT TRUNCATED AT 400 WORDS)

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