Contractile and electrical properties of human motor units in neuropathies and motor neurone disease

Milner-Brown, H. S.; Stein, Richard B.; Lee, R. G.

doi:10.1136/jnnp.37.6.670

Cited by 56 publications

(25 citation statements)

References 15 publications

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“…As in the current study, the EMG potentials might be up to ten times the normal size {23, 251, but the enlarged units were not found to produce more force [23]. The enlarged motor units in motoneuron disease appeared to be less efficient contractile units, in contrast to the patients with spinal cord injuries whose enlarged unit EMGs were matched by an increase in unit twitch forces.…”

Section: Adaptive Changes In Motor Units After Spinul Injmymentioning

confidence: 77%

Motor unit numbers and contractile properties after spinal cord injury

Yang

Stein

Jhamandas

et al. 1990

Annals of Neurology

107

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The number of motor units in the thenar muscle group was estimated in 11 patients with cervical spinal cord injuries. The surface electromyogram and twitch force, in response to maximal stimulation of the median nerve was divided by the average surface electromyogram and twitch of single units. The average single unit size was obtained by intramuscular microstimulation of motor nerve branches and by graded whole nerve stimulation, which provided three independent estimates, two based on the electromyogram and one based on force. The motor unit estimates from the patients covered a wide range. Some had essentially normal motor units both in numbers and contractile properties, while others had varying reductions in numbers of units. Those patients who showed a large reduction in motor unit numbers also had greatly enlarged units, which produced an average of up to sixfold the normal force. These enlarged units summed to produce maximal compound action potentials and twitches that were sometimes indistinguishable from normal. Magnetic resonance imaging scans of the cervical spine obtained from some patients provided independent evidence that patients with low motor unit counts had sustained direct injury to the anterior aspect of the spinal cord at the relevant segmental levels. Some patients showed a normal number of motor units long after the injury. No evidence of transneuronal degeneration could be demonstrated in the thenar group in these patients with the current techniques.

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Section: Adaptive Changes In Motor Units After Spinul Injmymentioning

confidence: 77%

Motor unit numbers and contractile properties after spinal cord injury

Yang

Stein

Jhamandas

et al. 1990

Annals of Neurology

107

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“…McComas and his colleagues [241 reported that some patients with severe denervation of the extensor hallucis brevis muscle exhibited a diminished twitch tension amplitude; Milner-Brown et a1 [27] did not study the whole muscle, only single motor units.…”

Section: Discussionmentioning

confidence: 98%

Dynamic properties of partially denervated muscle

Miller

1979

Annals of Neurology

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The mechanical and electrical properties of the partially denervated first dorsal interosseous muscle were measured in 14 patients and 14 normal control subjects. The following variables were studied during isometric contraction: maximum voluntary contraction; maximum rate of rise of tension in a rapid voluntary contraction; amplitude, rate of rise, time to peak, and duration of peak of the compound muscle action potential; twitch force, maximum rate of rise, contraction time, and half-relaxation time; and tetanic (50 Hz) force, rate of rise, and tetanus/twitch ratio. The force produced during repetitive stimulation of the ulnar nerve at 10, 20, 50, and 100 impulses per second was also analyzed. The major findings were: (1) decreased load bearing (voluntary contraction, twitch, and tetanus), (2) prolonged twitch contraction times and half-relaxation times, (3) decreased tetanus/twitch ratio, and (4) preserved rate of rise of tension.

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“…If a motoneurone dies as a result of a disease process, while others supplying adjacent muscle fibres remain healthy, reinnervation can take place immediately by the formation of sprouts which would only have to grow a fraction of a millimetre. In this way, the twitch tension of motor units would be increased above normal levels in polio' patients or in other forms of motoneurone disease (Milner-Brown et al 1974). Similarly, after partial denervation in experimental animals, sprouting motoneurones can increase their peripheral field of innervation at least 5 times (Brown & Ironton, 1978).…”

Section: Discussionmentioning

confidence: 99%

“…In one of the few human studies where both e.m.g. and tension were assessed after reinnervation, Milner-Brown, Stein & Lee (1974) found greatly increased e.m.g. signals with little or no increase in twitch tensions.…”

Section: Discussionmentioning

confidence: 99%

Time course and extent of recovery in reinnervated motor units of cat triceps surae muscles

Gordon

1982

The Journal of Physiology

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100

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SUMMARY1. Nerve and muscle properties were studied in single motor units of triceps surae muscles in the cat using chronic recording techniques and intramuscular microstimulation. Recordings were made before and at intervals up to 18 months after a nerve was sectioned and sutured either to its distal stump (nerve-nerve suture) or to a muscle directly (nerve-muscle suture). Thus, each nerve and muscle served as its own control for recovery after reinnervation.2. Following a delay all muscles recovered their preoperative tension after nerve-nerve suture with a single exponential having a time constant of 1-2 months. Only half the muscles recovered their preoperative tensions after nerve-muscle sutures. Muscles which did not recover fully also had a slower time course of recovery.3. The estimated number of motor units did not increase significantly later than 2 months after nerve section and suture. Further recovery of muscle tension is due to increased unit tension, rather than increasing numbers of reinnervated motor units. Unit tension recovered completely in all muscles, but did not become enlarged, even when muscles apparently remained partially denervated.4. The latency of compound nerve potentials often recovered completely, although the amplitude of the potential remained depressed. Single motor axonal potentials recovered to control levels after reinnervation of muscle with a time constant similar to that for the recovery of motor unit tension. Therefore, two distinct populations of motor axons contribute to the compound potential: reinnervating axons whose size recovers fully, and disconnected axons which remain atrophic. Incomplete recovery of the compound potential amplitude mainly results from a failure of all axons to remake peripheral connexions.5. Thus, formation of functional nerve-muscle connexions completely reverses the effects of axotomy on nerve and muscle. Reinnervated motor units recovered their preoperative size, whether or not much of the muscle remained denervated.

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Contractile and electrical properties of human motor units in neuropathies and motor neurone disease

Cited by 56 publications

References 15 publications

Motor unit numbers and contractile properties after spinal cord injury

Motor unit numbers and contractile properties after spinal cord injury

Dynamic properties of partially denervated muscle

Time course and extent of recovery in reinnervated motor units of cat triceps surae muscles

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