Single Motor Unit Potentials Research Articles

Computer method for the analysis of evoked motor unit potentials. I. Control subjects and patients with myasthenia gravis.

An on-line computer method is described for the isolation of single motor unit potentials, evoked by stimulation of the anterior tibial nerve at the ankle, from the compound action potential recorded from surface electrodes over the extensor digitorum brevis muscle. The latencies, durations, amplitudes, and areas of the potentials were measured in a group of control subjects and patients with myasthenia gravis. In myasthenic patients there is a significant reduction in the durations of motor unit potentials and a significant increase in latencies while their amplitudes and areas remain unchanged. The results are consistent with the presence of a `terminal neuropathy' in myasthenia gravis.

Disturbances in the voluntary recruitment order of anterior tibial motor units in bradykinesia of Parkinsonism.

The recruitment of motor units is studied with an electromyographic technique for secure identification of single motor unit potentials. It has been shown in previous studies that the recruitment order is different in tonic and in phasic activities; in tonic activity the recruitment order is stable and low frequency units are always recruited before high frequency units; in phasic activity, however, the recruitment order is unstable and units with a higher frequency range may be recruited before units with lower frequency range. In this investigation the shifts between tonic and phasic recruitment order in voluntary contraction were compared in normal subjects and in patients with severe bradykinesia of Parkinsonism. Upon initiation of a voluntary contraction in a normal subject, phasic recruitment order may be used for a few 100 msec but tonic recruitment order then takes over. In bradykinetic patients, however, this shift from phasic to tonic recruitment order is delayed. After termination of tonic voluntary contraction in a normal subject, phasic recruitment order can again be used after a few seconds. In bradykinetic patients, however, the shift back from tonic to phasic recruitment order is also delayed. In favourable experimental situations the shift from phasic to tonic recruitment order can be normalized by passive stretch of the muscle and the shift from tonic to phasic recruitment pattern by unloading the muscle. It is discussed whether the pathological recruitment in bradykinesia might be due to disturbed gamma loop function.

A spectral analysis of single motor unit potentials from human extraocular muscle.

A spectral analysis of single motor unit potentials from the human medial rectus extraocular muscle is described. The analysis was performed by first averaging individual single motor unit potentials and then subjecting the average to Fourier analysis using a digital computer. The portion of the spectrum between 300 Hz and 2.8 kHz has definite bandpass characteristics with -3-dB points for the low-and high-frequency sides equal to 470 Hz and 1.4 kHz, respectively. The spectrum provides some insight into the characteristics of a filter that would provide an indication of the occurrence of single unit potentials in an interference electromyogram.

Temporal Characteristics of Velopharyngeal Muscle Function

Temporal characteristics of palatoglossus and palatal levator muscle action in nasal consonant production were studied in seven Swedish speakers. Single motor unit potentials from these muscles were detected by inserted wire electrodes, stored on magnetic tape, and later recorded on light-sensitive paper for analysis. Results suggest that (1) the palatoglossus contracts to lower the palate actively for nasal consonant production; (2) there is a simultaneous relaxation of the palatal levator; (3) the EMG data show considerable temporal variability in the face of quite invariant acoustic data; and (4) in spite of the temporal variability, there is enough consistency to allow the development of a simple model of palatal coarticulation. Specifically, we suggest that for the production of nasals the palatal musculature functions rather grossly. The levator relaxes its activity in a gatelike fashion, allowing a temporal space during which the palate is easily lowered. During the open phase of the gate a slight pull is provided by the paltoglossus to assist in palatal lowering. During this “gating” and “pulling” process the articulators function for the actual production of the nasal. The position of the “gate” and its concomittant “pull” vary temporally with respect to the acoustic signal of the nasal in a highly predictable manner, largely dependent upon intraoral pressure requirements of adjacent phonemes.

Volitionally controlled single motor units in human finger muscles

Experiments were carried out on human subjects to investigate whether they could voluntarily isolate motor units in finger muscles, and also to investigate quantitatively the discharge frequencies of the singled-out motor units. (1) Territory of single motor unit potentials in m. opponens pollicis and m. abductor pollicis brevis extends longitudinally from the proximal to the distal end of the muscles, 9.0–22.3 mm transversely and 4.5–10.4 mm vertically. (2) When the muscle contracted gently (less than 20% of the maximal tension of the muscle), several motor units appeared. The subjects could isolate voluntarily 209 of 286 motor units (73.0%), within 30 min, on command from the experimenter. The remaining 77 units (27.0%) could not be isolated within this time limit. (3) The subjects were given reference frequencies such as 0.5, 1, 2, 3, 4, 5, 8, 10, 11, 15, 18, 20 and 25 c/sec, both on cathode-ray oscilloscope and through audio speaker for 10 sec, and were then asked to discharge the isolated motor unit at as nearly as possible the given frequencies. Frequencies such as 8, 10, 11 and 15 c/sec were ‘well’ performed in most units, 0.5, 1 and 18 c/sec were ‘well’ performed in some units but not in others and 2, 3, 4, 5 and 25 c/sec were ‘poorly’ performed in almost all units.

A method of recording from single muscle fibers or motor units in human skeletal muscle

It is possible to record single muscle fiber and single motor unit potentials with a tungsten microelectrode inserted percutaneously (without discomfort) into human muscle. Potentials averaging 10–12 mv, 2–4 msec in duration, have been recorded from such muscles as the gastrocnemius and pectoralis major. Firing of the motor units can be followed almost to a maximum isometric contraction without the action potentials being lost in a mass of other motor unit potentials. A technique has also been developed whereby the position of a microelectrode in a human muscle during isometric contraction can be controlled by means of a micromanipulator. The possibility of inserting hard metal microelectrodes into human skeletal muscle percutaneously and positioning them with a micromanipulator substantially widens the range of the experimental work that can be carried on to elucidate the electrophysiological phenomena concerned in human skeletal muscle contraction. intramuscular tungsten microelectrode; isotonic and isometric contraction measurement Submitted on August 2, 1963

Comparison of different needle leads in EMG recording from a single site

Single fibrillation and motor unit potentials have been recorded in various lead combinations by double-core concentric needle electrodes and double-tip unshielded electrodes. The results indicate that the conventional single-core needle is practically as valid as the monopolar needle in recording local muscle activity in the sense that any “distortion” of activity form at the shielded core tip is negligible as compared to the variability of potential form in blind monopolar or shielded needle placement. A general theoretical evaluation of needle electrode leads is described. The related physiological significance of the potentials they record is discussed as are the general advantages and disadvantages of monopolar, single-core concentric, and double-core concentric needles.