Recruitment Patterns of Motor Units in Speech Production

1981 ◽  
Vol 24 (4) ◽  
pp. 567-576 ◽  
Author(s):  
Anne Smith ◽  
Gerald N. Zimmermann ◽  
Paul J. Abbas
Keyword(s):  
Speech Production ◽  
Human Subjects ◽  
Motor Units ◽  
Action Potential Amplitude ◽  
Single Muscle ◽  
Single Motor Units ◽  
Jaw Opening ◽  
Intramuscular Electrodes ◽  
Recruitment Patterns ◽  
Underlying Mechanisms

Single motor units were recorded with intramuscular electrodes in sites selected to isolate units of the mentalis muscles of two human subjects. Order of recruitment of three groups of motor units was analyzed during repetition of syllables. Within each group motor units showed variable patterns of recruitment over repeated utterances. These recruitment patterns of labial motor units and the patterns observed by Sussman et al. in a jaw opening muscle are used to illustrate issues critical to interpretation of recruitment patterns of motor units active during speech. From extant data, inferences about the size of the motor units active cannot be made; however, the variability of recruitment patterns has significance for hypotheses about the underlying mechanisms of recruitment. Discussion includes the question of the size of motor units as inferred from action potential amplitude, differences in methodology between experiments in speech and those often used to interpret them, and the extent to which it is possible to isolate motor units from a single muscle in electromyography of facial muscles.

EMG Recording in Human Lip Muscles

1986 ◽  
Vol 29 (2) ◽  
pp. 256-266 ◽  
Author(s):  
Claudia Blair ◽  
Anne Smith
Keyword(s):  
Human Subjects ◽  
Motor Units ◽  
Single Muscle ◽  
Recording Site ◽  
Lower Lip ◽  
Anatomical Features ◽  
Anatomical Data ◽  
Movement Performance ◽  
Electrophysiological Method ◽  
Intramuscular Electrodes

Electromyography, recording the electrical activity of muscles, is an electrophysiological method that has been used widely in the study of movement performance by human subjects. Borrowing from the tradition of electromyographic studies of limb muscles, investigators interested in speech production have used the method to address many important experimental questions. Unfortunately, data recorded from craniofacial muscles generally have been discussed without reference to problems of interpretation that could arise due to the unique anatomical features of the muscles, particularly the lip muscles. Anatomical data show that the fibers of different muscles of the lips are interdigitated so that fibers with differing spatial orientation typically are found within a small section of lower lip tissue. The anatomical data are consistent with results of physiological studies of the lower lip muscles that have suggested that motor units with different physiological characteristics are found within a single recording site. Together, the anatomical and electrophysiological data suggest that, even with intramuscular electrodes, the probability of recording from a single muscle of the lip in isolation is extremely low. The fact that the activity of more than one muscle is likely to be sampled critically determines the nature of the conclusions that can be drawn from the data.

Change in recruitment order of motor units in human parasternal intercostal muscles with sleep state

1993 ◽  
Vol 74 (6) ◽  
pp. 2718-2723 ◽  
Author(s):  
W. A. Whitelaw ◽  
K. P. Rimmer ◽  
H. S. Sun
Keyword(s):  
Sleep Stage ◽  
Human Subjects ◽  
Motor Units ◽  
Excitatory Input ◽  
Sleep State ◽  
Intercostal Muscles ◽  
Intramuscular Electrodes ◽  
Normal Human ◽  
Low Threshold ◽  
Recruitment Order

Recruitment order of individual motor units in the early part of inspiration in parasternal intercostal muscles was observed in normal human subjects during wakefulness and non-rapid-eye-movement sleep. Electromyograms from bipolar fine wire intramuscular electrodes were recorded while the subjects lay supine in a sleep laboratory, and sleep stage was determined by polysomnography. From wakefulness to sleep there were numerous examples of shifts in order of recruitment among the low threshold units of early inspiration. There were corresponding shifts in the order of derecruitment of these units. Analysis of frequency of firing of units also suggested that the levels of excitatory input to one unit of a pair could be altered relative to the level of input of the other one. The data imply that there are at least minor differences in distribution of excitatory inputs from various sources among motoneurons of this muscle pool.

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.

Voluntary hyperventilation changes recruitment order of parasternal intercostal motor units

1987 ◽  
Vol 62 (1) ◽  
pp. 187-193 ◽  
Author(s):  
T. W. Watson ◽  
W. A. Whitelaw
Keyword(s):  
Human Subjects ◽  
Motor Units ◽  
Quiet Breathing ◽  
Rib Cage ◽  
Voluntary Hyperventilation ◽  
Single Motor ◽  
Intercostal Muscles ◽  
Single Motor Units ◽  
Normal Human ◽  
Recruitment Order

The order of recruitment of single-motor units in parasternal intercostal muscles during inspiration was studied in normal human subjects during quiet breathing and voluntary hyperventilation. Electromyograms were recorded from the second and third intercostal spaces by means of bipolar fine wire electrodes. Flow at the mouth, volume, end-expired CO2, and rib cage and abdominal anterior-posterior diameters were monitored. Single-motor units were identified using criteria of amplitude and shape, and the time of first appearance of each unit in each inspiration was noted. Hyperventilation was performed with visual feedback of the display of rib cage and abdomen excursions, keeping the ratio of rib cage to abdominal expansion. Subjects were normocapnic in quiet breathing and developed hypocapnia during hyperventilation. Recruitment order was stable in quiet breathing, but in some cases was altered during voluntary hyperventilation. Some low threshold units that fired early in the breath in quiet breathing fired earlier at the beginning of a period of voluntary hyperventilation but progressively later in the breath as hyperventilation went on, whereas later firing units moved progressively toward the early part of inspiration. This suggests that different groups of motoneurons in the pool supplying parasternal intercostal muscles receive different patterns of synaptic input.

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.

Evidence for Strong Synaptic Coupling Between Single Tactile Afferents From the Sole of the Foot and Motoneurons Supplying Leg Muscles

2005 ◽  
Vol 94 (6) ◽  
pp. 3795-3804 ◽  
Author(s):  
James B. Fallon ◽  
Leah R. Bent ◽  
Penelope A. McNulty ◽  
Vaughan G. Macefield
Keyword(s):  
Human Subjects ◽  
Motor Units ◽  
Glabrous Skin ◽  
Reflex Modulation ◽  
Type I ◽  
Type Ii ◽  
Synaptic Coupling ◽  
Single Motor Units ◽  
Low Threshold ◽  
Sole Of The Foot

It has been known for some time that populations of cutaneous and muscle afferents can provide short-latency facilitation of motoneuron pools. Recently, it has been shown that the input from individual low-threshold mechanoreceptors in the glabrous skin of the hand can modulate ongoing activity in muscles acting on the fingers via spinally mediated pathways. We have extended this work to examine whether such strong synaptic coupling exists between tactile afferents in the sole of the foot and motoneurons supplying muscles that act about the ankle. We recorded from 53 low-threshold mechanoreceptors in the glabrous skin of the foot via microelectrodes inserted percutaneously into the tibial nerve of awake human subjects. Reflex modulation of ongoing whole muscle electromyography (EMG) was observed for each of the four classes of low-threshold cutaneous mechanoreceptors (17 of 21 rapidly adapting type I; 2 of 4 rapidly adapting type II; 7 of 18 slowly adapting type I; and 4 of 10 slowly adapting type II). Reflex modulation of the firing probability in single motor units (5 of 11) was also observed. These results indicate that strong synaptic coupling between tactile afferents and spinal motoneurons is not a specialization of the hand and emphasizes the potential importance of cutaneous inputs from the sole of the foot in the control of gait and posture.

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