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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Composite group Ia excitatory postsynaptic potentials (EPSPs) produced by heteronymous nerve stimulation were recorded from triceps surae motoneurons of barbiturate-anesthetized cats. Motoneuron rheobase, input resistance, and axonal conduction velocity were measured, and motor units were classified on the basis of the mechanical responses of their muscle units. 2. The amplitude of EPSPs recorded from 33 medial gastrocnemius (MG) motoneurons ranged from 0.6 to 4.3 mV. The mean EPSP amplitude differed among the major MG motor-unit types, increasing in the order fast twitch, fast fatiguing (FF); fast twitch, fatigue resistant (FR); slow twitch, fatigue resistant (S) (FF less than FR less than S). The amplitude of EPSPs recorded from 15 soleus motoneurons ranged from 0.3 to 3.4 mV, with a mean of 1.4 mV. 3. Presynaptic inhibition of EPSPs was produced by trains of conditioning volleys in the posterior biceps-semitendinosus (PBST) nerve. In 33 MG cells PBST conditioning stimulation reduced the amplitude of EPSPs by 11-50%, with a mean inhibition of 27%. The amplitude of EPSPs in 15 soleus motoneurons was decreased by 5-84%, with a mean inhibition of 37%. 4. When the magnitude of presynaptic inhibition was expressed as percent inhibition, there was no relation between presynaptic inhibition and either motor-unit type or the amplitude of the EPSP. However, when presynaptic inhibition was expressed as the absolute amount of inhibition in millivolts, the magnitude of inhibition was highly correlated with EPSP amplitude both across the entire triceps surae population (MG, lateral gastrocnemius, soleus) as well as within each muscle population. This correlation was also significant within the MG FF and FR motor-unit populations. 5. We conclude that EPSP amplitude and not motor-unit type is the major determinant of the magnitude of presynaptic inhibition. However, because of the effect of motor-unit type on EPSP amplitude, the net effect is that presynaptic inhibition increases in the order FF less than FR less than S.
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PMID:Presynaptic inhibition, EPSP amplitude, and motor-unit type in triceps surae motoneurons in the cat. 685 61

The discharge properties on maintained maximal voluntary effort, axonal conduction velocity (a.c.v.) and contraction time (c.t.) of single human motor units were studied. Electromyographic (EMG) techniques were used and sufficient selectivity was obtained after repeated lesions to the terminal nerve twigs and consequent collateral sprouting, or by blocking the main muscle nerve in subjects with an accessory nerve supplying just one or a few units, or using high impedance wire electrodes. Most units with a.c.v. above 45 m/s and c.t. below 50 ms had maximal voluntary firing rates of about 50 Hz. On prolonged maximal effort, however, their rates rapidly decreased and after some seconds to a minute they ceased to respond tonically. As long as their motoneurons fired their EMG potentials were mainly intact and their twitch tension was significant. Most units with a.c.v. below 40 m/s and c.t. above 60 ms fired initially at 30 Hz, decreased slowly in firing rate and continued at 20 Hz for some minutes. We conclude that there is a central fatigue of units with short c.t. and high a.c.v. which protects their peripheral regions from severe exhaustion, but that there is no significant central fatigue of units with long c.t. and low a.c.v. We emphasize, however, that most units are intermediate in their properties.
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PMID:Firing properties of single human motor units on maintained maximal voluntary effort. 691 69

The central neural hearing disorders - in contrast to central cortical lesions - can be concretely defined audiometrically, and they can be localized realiably within the 2nd-4th neurons. For this purpose a definite test program is needed; especially indicative are the behavior of the acoustico-facial stapedius reflex and the results in dichotic discrimination and ERA. SISI and difference limen mostly point to a neural dysfunction, but - in distinct patterns of impairment - they may correspond to the picture of a peripheral hearing disorder as well. A fatigue of hearing apparently only appears if the myelin is damaged, at - perhaps additional - axonal lesions it shows up less clearly or not at all. The deficiency pattern of the stapedius reflex reflects up less clearly or not at all. The deficiency pattern of the stapedius reflex reflects the course of the reflex arc within the brain stem; accordingly, more central lesions of the auditory pathway do not affect the reflex. ERA mostly makes perceivable a lesion of synchronization, which only becomes noticeable at fast repetition rates with ultra short stimuli (1/4 ms), i.e., solely in the responses of the brain stem. The cortical responses, on the contrary, are not impaired more than the subjective threshold renders to be expected, they even show the same values of the pure tone audiogram. The dichotic discrimination is nearly always disturbed unilaterally, at processes of the brain stem homolaterally, at cortical foci predominantly leftside, perhaps because the left hemisphere dominates in speech discrimination. The otologist should know how to make use of the possibility of neuro-otologic diagnostics.
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PMID:Aspects in diagnostics of central neural hearing disorders. 697 31

In anaesthetized cats, alpha motoneurones of m. gastrocnemius medialis were activated by maintained currents that were injected via an intracellular microelectrode. There was a statistically significant correlation between the threshold current for maintained repetitive firing and axonal conduction velocity. These findings confirmed that slow-axoned motoneurones tend to be more excitable than those with faster axons. Among fast-twitch motoneurones of about the same size as judged by their axonal conduction velocity, the average threshold current was about twice as high for cells innervating fatigue-sensitive muscle fibres (FF units) than for those supplying more fatigue-resistant ones (FR units).
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PMID:Threshold current for repetitive impulse firing in motoneurones innervating muscle fibres of different fatigue sensitivity in the cat. 730 7

1. A sublethal quantity of black widow spider venom was injected into the calf muscles of mice. After 30 min to 6 weeks soleus muscles were examined by light and electron microscopy and by electrophysiological techniques. 2. Within 30 min motor nerve terminals were swollen and depleted for synaptic vesicles and by 6 h were disrupted and engulfed by Schwann cells. By 24 h every end-plate examined was denervated. Some preterminal myelinated axons also showed degenerative changes. 3. Re-innervation was first seen at 2 days. By 3 days axon terminals were present at most end-plates and by 8 days their morphology was nearly normal. The normal pattern of innervation of the muscle was re-established in that axons re-innervated their original end-plates and very few ultraterminal axonal sprouts were found. 4. Physiological study showed complete failure of transmission and absence of miniature end-plate potentials (m.e.p.p.s) and end-plate potentials (e.p.p.s) until day 3, when muscles responded weakly to indirect stimulation and m.e.p.p.s were recorded at 30% and e.p.p.s at 40% of fibres. The mean quantal content of e.p.p.s was low and there was rapid fatigue on repetitive stimulation. Extrajunctional sensitivity to acetylcholine developed within 1 day, was maximal at 3 days and declined to normal at 12-14 days. 5. The proportion of fibres at which m.e.p.p.s and e.p.p.s were recorded returned to normal by day 6 and mean quantal content was normal by day 9. 6. These findings show that the re-innervation of original end-plates is of importance in facilitating the rapid return of transmission to normal levels and limiting the extent of axonal growth.
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PMID:The neuromuscular junction of the mouse after black widow spider venom. 732 Aug 66

Synaptic glutamate release involves the accumulation of cytoplasmic glutamate in synaptic vesicles, whereafter it is released by triggered exocytosis. As glutamatergic terminals are known to be functionally diverse it was of interest to examine whether the presynaptic glutamate supply differs between individual axon terminals with distinct release properties. The glutamatergic terminals in the crustacean neuromuscular system system comprise a "phasic" type which shows fatigue of release during repetitive stimulation, and a "tonic" type which can maintain transmission for long periods. Quantitative immunogold analysis showed that the axons in a tonic nerve innervating slow muscles in the abdomen contained two times higher levels of glutamate labeling over axoplasmic matrix and over mitochondria, as compared to the corresponding elements in a phasic nerve. Similar results were obtained when adjacent phasic and tonic axons in a mixed nerve innervating leg muscles were compared. In the terminal regions of tonic and phasic axons the glutamate labeling differed correspondingly over axoplasmic matrix and mitochondria, while the synaptic vesicles showed a similar strong accumulation of labeling in both types of terminal. The level of labeling for glutamine, a glutamate precursor, was closely similar in phasic and tonic axons. The axoplasmic glutamate concentration was estimated to be in the low millimolar range, through comparison with coprocessed conjugates with known glutamate concentration. These results show that fatigue-resistant tonic axons and terminals contain higher levels of glutamate than fatiguable phasic axons, presumably representing an adaptation to the markedly different impulse activities in the two types of neuron. The axonal glutamate concentrations are in the range of the Km value for vesicular glutamate transport. Thus in tonic axons the high glutamate level appears to promote an efficient refilling of synaptic vesicles during sustained release, while in phasic axons the refilling should be slower which is compatible with an infrequent release.
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PMID:Presynaptic glutamate levels in tonic and phasic motor axons correlate with properties of synaptic release. 747 71

Hyperthyroidism is a common endocrinologic disorder affecting many organ systems. Musculoskeletal and neurological involvement present themselves as fatigue, muscle weakness and paralysis. Electromyography (EMG) is essential for differential diagnosis of muscle weakness. Well defined neuropathy and myopathy have been described in these patients. In the present study 17 hyperthyroid patients were evaluated with electrophysiological tests in addition to physical and neurological examinations and biochemical laboratory studies. Needle EMG, motor and sensory conduction velocities, median and tibial somatosensory evoked potentials (SEP) were studied. For assessment of the activity of disease clinical status, neurological symptom and disability scores and serum T3, T4 and TSH levels were examined. Statistical analysis of neuroelectrophysiological findings of the patient and the control groups yielded meaningful difference in the needle EMG, sensory conduction velocity and evoked potential findings. Abnormalities were observed in 80% of the proximal muscles besides polyphasic potentials that were seen in 20% of the extensor digitorum brevis muscle. Median, ulnar and sural nerve sensory action potential amplitudes were found to be lower than that of the control group. Sural sensory nerve conduction velocity of patients was decreased in 35.5%, prolongation of median SEP latencies and increase in the amplitudes were not however statistically significant. Prolongation of Tibial SEP N1, P2 latencies were seen in 47%, amplitudes of N1 were increased in 88.2%, P2 in 58.8%, N2 in 47%. The thyroid clinical status score was correlated with Tibial SEPs amplitude. These findings suggest the presence of an initial axonal type of mild polyneuropathy. As a conclusion electrophysiological studies can be useful in the diagnosis of asymptomatic polyneuropathy in hyperthyroid patients.
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PMID:Neuroelectrophysiological evaluation of untreated hyperthyroid patients. 753 51

To understand the mechanism of post-poliomyelitis muscular atrophy (PPMA) and the post-polio syndrome (PPS) in general, we performed the following studies: (1) histopathology in spinal cord sections from patients who died 9 days to 44 years after acute paralytic poliomyelitis; (2) enzyme histochemistry, immunocytochemistry (for lymphocyte subsets, MHC antigens and N-CAM) and polymerase chain reaction (PCR) for poliovirus RNA in the muscle biopsies from symptomatic or asymptomatic muscles of post-polio patients; (3) determination of lymphocyte subsets and circulating IgG or IgM antibodies against GM1 and poliovirus; (4) virological studies in the spinal fluid for oligoclonal bands and search for poliovirus genome with PCR; (5) electrophysiological studies including single fiber EMG, fiber density and macro-EMG; and (6) [31P] exercise MRS spectroscopy on previously affected muscles to search for a metabolic correlate of fatigue. These studies concluded that in PPS a continuing dysfunction is present in the spinal cord motor neurons, resulting in ongoing muscle denervation and reinnervation first evident at the axonal branch points. Symptoms are related to attrition of the oversprouting motor neurons which after a period of time cannot support all their axonal sprouts, resulting in failure of re-reinnervation. In some patients with PPS there is also an ongoing immune activation and presence of defective viral particles in the spinal fluid. However, their role in the pathogenesis of PPS is presently unknown.
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PMID:Pathogenetic mechanisms of post-polio syndrome: morphological, electrophysiological, virological, and immunological correlations. 761 26

This communication concerns a 55 year old woman with a 5 year history of chronic progressive multiple sclerosis (MS) in whom a single external application of extremely low magnetic fields (MF) (7.5 picoTesla; 5 Hz frequency) of 20 minutes duration resulted in a rapid improvement in symptoms including vision, cerebellar symptomatology (ataxia and dysarthria), bladder functions, mood, sleep, cognitive functions and fatigue. Improvement in the patient's symptoms was associated with normalization of the pretreatment abnormal visual evoked potential (VEP) latencies within 24 hours after magnetic treatment. The rapid normalization of the VEP latencies suggests that recovery did not occur as a result of remyelination but probably was related to enhancement of neurotransmitter functions. MF have been shown to alter cellular calcium metabolism which may facilitate axonal conduction in demyelinating plaques. Furthermore, as MF affects the release of the pineal gland's principal hormone, melatonin, which influences the release of monoamines, it is also hypothesized that the effects of picoTesla MF in MS are partly mediated by the pineal gland which has recently been implicated in the pathogenesis of MS (Sandyk, 1992 a).
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PMID:Rapid normalization of visual evoked potentials by picoTesla range magnetic fields in chronic progressive multiple sclerosis. 781 17

In the context of an analysis concerning factors of importance for the relative contributions of recruitment and rate gradation of muscle force, the distribution of electrical excitability was analyzed for medial gastrocnemius (MG) motoneurones of rat and cat. The experimental data came from previously collected intracellular measurements in animals anaesthetized with pentobarbitone. Electrical excitability was measured as the threshold (nanoamperes) for single spike generation (rheobase) in rat and for maintained repetitive firing (rhythmic threshold) in cat. Furthermore, the data included measurements of axonal conduction velocity and of contractile properties of the muscle units innervated by the studied motoneurones. The units were categorized into types S (slow-twitch, fatigue-resistant), FR (fast-twitch, fatigue-resistant) and FF (fast-twitch, fatiguable) on the basis of the combined criteria of twitch-speed and sensitivity to fatigue. We confirmed that, in spite of the presence of normal-looking symmetrical distributions of axonal conduction velocity, there was a positive skew in the distribution of electrical excitability (relatively high numbers of cells with low thresholds, few with high ones). Within each unit category (S, FR, FF), we ranked the motoneurones according to their relative electrical excitability and calculated the threshold difference between consecutive cells ("threshold spacing"). In accordance with the skewed distribution of electrical excitability, we found that the mean threshold spacing was ranked in the same way as the mean thresholds, i.e. S < FR < FF; the statistical analysis showed that, for cats as well as rats, small threshold spacing steps were significantly more common for S than for FF motoneurones.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Threshold-spacing in motoneurone pools of rat and cat: possible relevance for manner of force gradation. 789


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