Recruitment and Discharge Patterns of Single Motor Units During Speech Production

1977 ◽  
Vol 20 (4) ◽  
pp. 613-630 ◽  
Author(s):  
Harvey M. Sussman ◽  
Peter F. MacNeilage ◽  
Randall K. Powers
Keyword(s):  
Dynamic Range ◽  
Isometric Force ◽  
Discharge Rate ◽  
Motor Units ◽  
Size Principle ◽  
Single Motor ◽  
Single Motor Units ◽  
Movement Dynamics ◽  
Discharge Patterns ◽  
Anterior Belly

Recruitment and discharge patterns of single motor units (MUs) in the anterior belly of digastric were studied during speech in three subjects, using electrodes facilitating selective recording at high force levels. Fixed recruitment order was observed in over 99% of all comparisons. Later recruited units invariably possessed muscle action potentials of higher amplitude, suggesting that units were activated in accordance with the “size principle.” Additional evidence for this was that later recruited units, of a set of three studied during speech, motor unit training, and isometric force ramps, showed greater sensitivity to input, and greater dynamic range than earlier recruited units. Units in this set were much more sensitive to rapid changes in input associated with speech gestures than to static activation even at high force levels. Several significant relations between discharge characteristics and aspects of movement dynamics were observed, including relations between (1) recruitment interval (MU1 to MU3) and latency of mandibular lowering, (2) onset of initial discharge of MU1 and relative mechanical advantage of the mandible, (3) number of MUs active and velocity and displacement of the mandible, and (4) discharge rate of MU3 and velocity and displacement of the mandible.

Functional Activity of Superior Head of Human Lateral Pterygoid Muscle during Isometric Force

2005 ◽  
Vol 84 (6) ◽  
pp. 548-553 ◽  
Author(s):  
S. Ruangsri ◽  
T. Whittle ◽  
K. Wanigaratne ◽  
G.M. Murray
Keyword(s):  
Computer Tomography ◽  
Functional Activity ◽  
Isometric Force ◽  
Motor Units ◽  
Emg Activity ◽  
Single Muscle ◽  
Lateral Pterygoid Muscle ◽  
Functional Activities ◽  
Single Motor ◽  
Single Motor Units

There is controversy as to the jaw tasks for which the superior head of the human lateral pterygoid muscle (SHLP) becomes active. The aim was to describe the functional activities of SHLP single motor units (SMUs) during horizontal isometric force tasks. In 11 subjects, 48 SMUs were recorded from computer-tomography-verified SHLP sites during generation of horizontal isometric force in the contralateral (CL), protrusive (P), and ipsilateral (IL) directions and intermediate directions (CL-P, IL-P). In eight subjects, SHLP SMUs were active in CL, CL-P, and P. Qualitatively, SHLP EMG activity increased with increased isometric force. Forty-two SMUs were active in directions other than IL; 6 exhibited activity at IL and other directions. The similarity of these data to previous human lateral pterygoid (IHLP) data supports the notion that SHLP and IHLP should be regarded as a single muscle, with activities shaded according to the biomechanical demands of the task.

Behavior of motor units in human biceps brachii during a submaximal fatiguing contraction

1994 ◽  
Vol 76 (6) ◽  
pp. 2411-2419 ◽  
Author(s):  
S. J. Garland ◽  
R. M. Enoka ◽  
L. P. Serrano ◽  
G. A. Robinson
Keyword(s):  
Motor Unit ◽  
Biceps Brachii ◽  
Discharge Rate ◽  
Human Subjects ◽  
Absolute Threshold ◽  
Motor Units ◽  
Single Motor ◽  
Threshold Force ◽  
Single Motor Units ◽  
Discharge Rates

The activity of 50 single motor units was recorded in the biceps brachii muscle of human subjects while they performed submaximal isometric elbow flexion contractions that were sustained to induce fatigue. The purposes of this study were to examine the influence of fatigue on motor unit threshold force and to determine the relationship between the threshold force of recruitment and the initial interimpulse interval on the discharge rates of single motor units during a fatiguing contraction. The discharge rate of most motor units that were active from the beginning of the contraction declined during the fatiguing contraction, whereas the discharge rates of most newly recruited units were either constant or increased slightly. The absolute threshold forces of recruitment and derecruitment decreased, and the variability of interimpulse intervals increased after the fatigue task. The change in motor unit discharge rate during the fatigue task was related to the initial rate, but the direction of the change in discharge rate could not be predicted from the threshold force of recruitment or the variability in the interimpulse intervals. The discharge rate of most motor units declined despite an increase in the excitatory drive to the motoneuron pool during the fatigue task.

Responses of tendon organs to unfused contractions of single motor units

1985 ◽  
Vol 53 (1) ◽  
pp. 32-42 ◽  
Author(s):  
L. Jami ◽  
J. Petit ◽  
U. Proske ◽  
D. Zytnicki
Keyword(s):  
Discharge Rate ◽  
Motor Units ◽  
Stimulation Frequency ◽  
Dynamic Component ◽  
Single Motor ◽  
Single Motor Units ◽  
Discharge Rates ◽  
Visible Effect ◽  
Tendon Organs ◽  
Tendon Organ

The discharges of individual tendon organs of peroneus longus and tertius muscles were examined in anesthetized cats during stimulation of single motor units at frequencies that elicit unfused contraction (5-50/s). At these frequencies nearly all the fast-contracting motor units activating a tendon organ elicited responses whose discharge rates reproduced the stimulation frequency ("1:1 driving"), whereas slow-contracting motor units elicited responses in which the discharge rate was higher than the stimulation frequency. When a motor unit stimulated at 40/s developed a gradually potentiating tension, the tendon organ discharge could remain locked on stimulation frequency over an appreciable range of the increasing tension as if the receptor responded to the tension oscillations rather than to the mean level of tension. The only visible effect of the gradual increase in mean tension on the tendon organ response was a gradual decrease of the delay between each stimulus and the corresponding impulse. Driving of tendon organ discharge at the stimulation frequency occurred not only when relatively large oscillations were superimposed on a low level of static tension but also when the static component of the tension was quantitatively preponderant. These observations suggest that during unfused contractions the dynamic component of the stimulus (i.e., oscillation of tension) exerts a prevailing influence on the discharge pattern of tendon organs. Computed simulations of tendon organ responses confirmed that a relatively strong dynamic sensitivity could account for the observed behavior of the receptor.

Mechanical properties of single motor units in the anterior belly of the digastric

1977 ◽  
Vol 62 (S1) ◽  
pp. S15-S15
Author(s):  
Peter F. MacNeilage ◽  
H. M. Sussman ◽  
R. K. Powers ◽  
J. R. Westbury
Keyword(s):  
Mechanical Properties ◽  
Motor Units ◽  
Single Motor ◽  
Single Motor Units ◽  
Anterior Belly

scholarly journals Human stretch reflex pathways reexamined

2014 ◽  
Vol 111 (3) ◽  
pp. 602-612 ◽  
Author(s):  
Ş. Utku Yavuz ◽  
Natalie Mrachacz-Kersting ◽  
Oğuz Sebik ◽  
M. Berna Ünver ◽  
Dario Farina ◽  
...  
Keyword(s):  
Stretch Reflex ◽  
Discharge Rate ◽  
Human Subjects ◽  
Silent Period ◽  
Motor Units ◽  
Single Motor Unit ◽  
Single Motor ◽  
Reflex Responses ◽  
Single Motor Units ◽  
Discharge Rates

Reflex responses of tibialis anterior motor units to stretch stimuli were investigated in human subjects. Three types of stretch stimuli were applied (tap-like, ramp-and-hold, and half-sine stretch). Stimulus-induced responses in single motor units were analyzed using the classical technique, which involved building average surface electromyogram (SEMG) and peristimulus time histograms (PSTH) from the discharge times of motor units and peristimulus frequencygrams (PSF) from the instantaneous discharge rates of single motor units. With the use of SEMG and PSTH, the tap-like stretch stimulus induced five separate reflex responses, on average. With the same single motor unit data, the PSF technique indicated that the tap stimulus induced only three reflex responses. Similar to the finding using the tap-like stretch stimuli, ramp-and-hold stimuli induced several peaks and troughs in the SEMG and PSTH. The PSF analyses displayed genuine increases in discharge rates underlying the peaks but not underlying the troughs. Half-sine stretch stimuli induced a long-lasting excitation followed by a long-lasting silent period in SEMG and PSTH. The increase in the discharge rate, however, lasted for the entire duration of the stimulus and continued during the silent period. The results are discussed in the light of the fact that the discharge rate of a motoneuron has a strong positive linear association with the effective synaptic current it receives and hence represents changes in the membrane potential more directly and accurately than the other indirect measures. This study suggests that the neuronal pathway of the human stretch reflex does not include inhibitory pathways.

Muscle spindle discharge in response to contraction of single motor units

1983 ◽  
Vol 49 (2) ◽  
pp. 291-302 ◽  
Author(s):  
B. McKeon ◽  
D. Burke
Keyword(s):  
Muscle Spindle ◽  
Discharge Rate ◽  
Human Subjects ◽  
Motor Units ◽  
Muscle Spindles ◽  
Single Motor Unit ◽  
Single Motor ◽  
Twitch Contraction ◽  
Single Motor Units ◽  
Tendon Organ

1. In human subjects, microelectrode recordings were made from 25 muscle spindle afferents and two tendon organ afferents coming from muscles innervated by the peroneal nerve. 2. Stimulation at low intensity through the recording microelectrode activated efferent axons innervating motor units in close proximity to the muscle spindle or tendon organ. There was a clear alteration in the discharge of 17 afferents (15 muscle spindle, 2 tendon organ) in response to twitch contractions that involved only one, two, or three motor units. With three other afferents there was a less overt but statistically significant alteration in discharge rate by the twitch contraction of a single motor unit. 3. The sensitivity of 21 receptors (20 spindles, 1 tendon organ) to twitch contractions of anatomically close motor units was contrasted with their sensitivity to twitches of more remote motor units in the muscle. In no instance was the sensitivity to the contraction of remote motor units greater than that to the contraction of local motor units stimulated through the microelectrode; with remote stimulation many units usually had to be activated before the resulting twitch contraction altered the discharge of an afferent. 4. It is concluded that muscle spindles as well as tendon organs can play a role in monitoring the activity of motor units anatomically close to the receptor.

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