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Results for “MYONEURAL JUNCTION”

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At least 19 recordsLinked to original sources
PubMed1956

The ultrastructure of a reptilian myoneural junction.

Myoneural junctions in Anolis are characterized by the formation of troughs in the surface of the muscle fibers in which small branches of the terminal axon lie. The muscle surface membrane lining the troughs is thrown into complex branching and anastomosing folds, which compose the subneural apparatus of Couteaux. A compound membrane 500 to 700 A thick separates axoplasm from sarcoplasm at the endings. This consists of five distinct layers and is described in detail. A thin layer of cytoplasm (probably Schwann) separates terminal axoplasm from extracellular space at the surfaces of the junctional troughs. Terminal axoplasm lacks axoplasmic filaments and contains numerous vesicular or tubular appearing structures about 300 to 500 A in diameter. Both terminal axoplasm and sarcoplasm contain numerous mitochondria.

Axons↗
PubMed1973

Membrane specialization at an insect myoneural junction.

Myoneural junctions were examined in the asynchronous basalar flight muscle of the beetle Pachnoda ephippiata. The outer surface of the postjunctional membrane exhibits an array of prominent projections spaced at approximately 200 A intervals which arise directly from the outer dense lamina of the plasma membrane and extend part way across the junctional cleft. The projections follow irregularities in the contour of the postjunctional membrane precisely and they end abruptly near the edge of the junctional region. No separation can be resolved between the projections and the underlying trilaminar plasma membrane after a variety of preparative methods, and the projections therefore appear to be a component part of the membrane. This specialization, which is distinctly different from that at desmosomes and hemidesmosomes, occurs nowhere else on the surface of the muscle and is interpreted as a mosaic of specialized membrane subunits which probably include the receptor sites for the transmitter.

Animals↗
PubMed1977

Histochemical and electron microscopic observations on the myoneural junctions of rats with carbon disulfide induced polyneuropathy.

Myoneural junctions in the tibialis anterior muscle of rats with clinical signs of polyneuropathy induced with carbon disulfide were studied by light and electron microscopy. Histochemically demonstrable acetylcholinesterase (AChE; E.C. 3.1.1.7) activity was distributed similarly in the myoneural junctions of both the exposed and the control rats. In both groups intense enzyme activity was localized at the level of the post-synaptic membrane of the myoneural junction. The postsynaptic infoldings of the myoneural junctions of the exposed rats appeared normal. No enzyme activity was seen outside the zone of the myoneural junctions. The ultrastructure of the sub-sarcolemmal space, as well as the postsynaptic membranes of the myoneural junctions of the exposed animals, was normal. In the terminal axons signs of various degrees of degeneration were present, e.g., disappearance of the preterminal axoplasmic neurotubules, partial disappearance of synaptic vesicles, appearance of dense bodies, and even total disappearance or destruction of the terminal axons. Synaptic clefts were often widened with Schwann cell interposition. It thus seems that systemic carbon disulfide poisoning primarily alters the presynaptic structures of the myoneural junctions, while the postsynaptic side remains relatively intact, especially since the histochemical distribution of AChE in myoneural junctions was normal.

Acetylcholinesterase↗
PubMed1983

The distribution of myoneural junctions in the biceps brachii investigated by surface electromyography.

The location of the myoneural junction was investigated by a surface electromyogram. During a voluntary muscular contraction, an electrode array was placed on the skin overlying the muscle to detect myoelectric potentials propagating in both proximal and distal directions along the muscle fibers. The source of the propagating waves was presumed to mark the location of the myoneural junctions. The recordings were repeated to cover the whole muscle surface and the distribution of myoneural junctions was determined. Myoneural junctions in the biceps brachii were located nearly at the middle length of the muscle and were distributed in a zone across the muscle. The distribution showed differences in 3 subjects examined. In 1 subject, myoneural junctions occupied a single zone, while the other 2 subjects had 2 parallel zones separated by 10-20 mm. This information about the location of myoneural junctions is important for determining the electrode position in an electromyogram study.

Adult↗
PubMed2006

Familial risks for diseases of myoneural junction and muscle in siblings based on hospitalizations and deaths in sweden.

Diseases of the myoneural junction and muscle are disabling and some are life-threatening. Recent successes in the identification of the underlying genetic mechanisms have had profound implication for their diagnostics, treatment and classification. We define familial risks for siblings who were hospitalized for or deceased from diseases of the myoneural junction and muscle. A nationwide database on diseases of the myoneural junction and muscle was constructed by linking the Multigeneration Register on 0- to 69-year-old siblings to the Hospital Discharge Register and the Causes of Death Register from years 1987 to 2001. Standardized risk ratios (SIRs) were calculated for affected sibling pairs by comparing to those whose siblings had no diseases of myoneural junction and muscle. Among a total of 2307 patients, myasthenia gravis, muscular dystrophy and myotonic disorders were commonest diagnoses. The sibling risks for these disease were 22, 190 and 198, respectively, when a sibling was diagnosed with any disease of the myoneural junction and muscle. The concordant SIRs, both siblings presenting the same disease, were 42 for myasthenia gravis, 737 for muscular dystrophy, 2000 for congenital myopathy, 1211 for myotonic disorder, 909 for periodic paralysis and 209 for unspecified myopathy. Only a few discordant sibling pairs were noted. The very high overall SIRs for the diseases of the myoneural junction and muscle imply that the sporadic forms of these diseases are relatively rare and these diseases are overwhelmingly heritable.

Adolescent↗
PubMed1951

Action of inhibitors at the myoneural junction.

1. A study is presented of the actions of certain inhibitors on the frog rectus abdominis muscle stimulated by acetylcholine. 2. A type of analysis has been developed which provides a reliable criterion for judging whether an inhibitor is competing with acetylcholine for receptors at the myoneural junction or whether acting by a different mechanism. 3. The "curares" are shown to act by competitive inhibition at the myoneural junction, confirming earlier work of others on the mode of action of curare. 4. Atropine acts as an inhibitor at the myoneural junction. The inhibition may be non-competitive or it may be complicated by an additional effect at some point other than the myoneural junction. 5. A possible mechanism for anomalous inhibitor effects is the action of a single compound at more than one locus in the Ach mechanism. Eserine exerts such a dual effect at the end-plate. 6. Some of the available electrical and chemical data have been correlated to make possible a partial explanation of the role of Ach in transmission at the myoneural junction.

Acetylcholine↗
PubMed1998

Two-dimensional configuration of the myoneural junctions of human masticatory muscle detected with matrix electrode.

Motor unit action potentials (MUAPs) propagate bidirectionally from the myoneural junction along the muscle fibre. The propagation of excitation within single motor units can be detected during sustained isometric contraction using a surface electrode array. Electromyographic (EMG) signals from an adjacent pair of contacts along the muscle fibres show a very similar wave form with a time shift. In the present study, EMG signals of the masseter and the temporal muscles were obtained from two male adults during clenching in the intercuspal position using the multichannel surface electrode with 17 x 11 contacts. The two-dimensional location of the myoneural junction for each column from the source of the propagation was estimated. Each of the myoneural junctions was located in the lower portion of the masseter muscle and in the upper portion of the temporal muscle. However, the junction was distributed within 10 mm along the muscle fibres at different contraction levels in each muscle. This noninvasive technique of multiple surface electrodes enabled us to add to knowledge of the anatomical structure of the masticatory muscles examined.

Action Potentials↗