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Science (New York, N.Y.) Mar 1967Reduced nicotinamide adenine dinucleotide tatrazolium reductase is abundant in cat intrafusal muscle fibers, whereas in the toad its activity is equal to that in...
Reduced nicotinamide adenine dinucleotide tatrazolium reductase is abundant in cat intrafusal muscle fibers, whereas in the toad its activity is equal to that in extrafusal fibers. Spindles of both species contain little fat. In sections stained for adenosine triphosphatase bound to myofibrils, two types of intrafusal muscle fibers appear in spindles of both the cat and toad.
Topics: Adenosine Triphosphatases; Animals; Anura; Cats; Histocytochemistry; Muscle Spindles; NAD; Oxidoreductases; Tetrazolium Salts
PubMed: 4289499
DOI: 10.1126/science.155.3768.1424 -
Experimental Physiology Jan 2024The goals of this review are to improve understanding of the aetiology of chronic muscle pain and identify new targets for treatments. Muscle pain is usually associated... (Review)
Review
The goals of this review are to improve understanding of the aetiology of chronic muscle pain and identify new targets for treatments. Muscle pain is usually associated with trigger points in syndromes such as fibromyalgia and myofascial syndrome, and with small spots associated with spontaneous electrical activity that seems to emanate from fibers inside muscle spindles in EMG studies. These observations, added to the reports that large-diameter primary afferents, such as those innervating muscle spindles, become hyperexcitable and develop spontaneous ectopic firing in conditions leading to neuropathic pain, suggest that changes in excitability of these afferents might make an important contribution to the development of pathological pain. Here, we review evidence that the muscle spindle afferents (MSAs) of the jaw-closing muscles become hyperexcitable in a model of chronic orofacial myalgia. In these afferents, as in other large-diameter primary afferents in dorsal root ganglia, firing emerges from fast membrane potential oscillations that are supported by a persistent sodium current (I ) mediated by Na channels containing the α-subunit Na 1.6. The current flowing through Na 1.6 channels increases when the extracellular Ca concentration decreases, and studies have shown that I -driven firing is increased by S100β, an astrocytic protein that chelates Ca when released in the extracellular space. We review evidence of how astrocytes, which are known to be activated in pain conditions, might, through their regulation of extracellular Ca , contribute to the generation of ectopic firing in MSAs. To explain how ectopic firing in MSAs might cause pain, we review evidence supporting the hypothesis that cross-talk between proprioceptive and nociceptive pathways might occur in the periphery, within the spindle capsule.
Topics: Humans; Muscle Spindles; Myalgia; Chronic Pain; Membrane Potentials; Neuralgia; Neurons, Afferent
PubMed: 38103003
DOI: 10.1113/EP090769 -
Brain Research Bulletin Mar 2008
Topics: Animals; Humans; Muscle Spindles
PubMed: 18355621
DOI: 10.1016/j.brainresbull.2007.11.017 -
Sheng Li Xue Bao : [Acta Physiologica... Feb 2013One of the most important and urgent issues in the field of space medicine is to reveal the potential mechanism underlying the disused muscle atrophy during the... (Review)
Review
One of the most important and urgent issues in the field of space medicine is to reveal the potential mechanism underlying the disused muscle atrophy during the weightlessness or microgravity environment. It will conduce to find out effective methods for the prevention and treatment of muscle atrophy during a long-term space flight. Increasing data show that muscle spindle discharges are significantly altered following the hindlimb unloading, suggesting a vital role in the progress of muscle atrophy. In the last decades, we have made a series of studies on changes in the morphological structure and function of muscle spindle following simulated weightlessness. This review will discuss our main results and related researches for understanding of muscle spindle activities during microgravity environment, which may provide a theoretic basis for effective prevention and treatment of muscle atrophy induced by weightlessness.
Topics: Animals; Hindlimb Suspension; Muscle Spindles; Muscle, Skeletal; Muscular Atrophy; Space Flight; Weightlessness Simulation
PubMed: 23426520
DOI: No ID Found -
ELife Dec 2020Despite decades of research, we lack a mechanistic framework capable of predicting how movement-related signals are transformed into the diversity of muscle spindle...
Despite decades of research, we lack a mechanistic framework capable of predicting how movement-related signals are transformed into the diversity of muscle spindle afferent firing patterns observed experimentally, particularly in naturalistic behaviors. Here, a biophysical model demonstrates that well-known firing characteristics of mammalian muscle spindle Ia afferents - including movement history dependence, and nonlinear scaling with muscle stretch velocity - emerge from first principles of muscle contractile mechanics. Further, mechanical interactions of the muscle spindle with muscle-tendon dynamics reveal how motor commands to the muscle (alpha drive) versus muscle spindle (gamma drive) can cause highly variable and complex activity during active muscle contraction and muscle stretch that defy simple explanation. Depending on the neuromechanical conditions, the muscle spindle model output appears to 'encode' aspects of muscle force, yank, length, stiffness, velocity, and/or acceleration, providing an extendable, multiscale, biophysical framework for understanding and predicting proprioceptive sensory signals in health and disease.
Topics: Animals; Computer Simulation; Female; Models, Biological; Movement; Muscle Contraction; Muscle Spindles; Rats; Rats, Wistar
PubMed: 33370235
DOI: 10.7554/eLife.55177 -
Muscle & Nerve Jul 2022The muscle relaxant methocarbamol and the antimyotonic drug mexiletine are widely used for the treatment of muscle spasms, myotonia, and pain syndromes. To determine...
INTRODUCTION/AIMS
The muscle relaxant methocarbamol and the antimyotonic drug mexiletine are widely used for the treatment of muscle spasms, myotonia, and pain syndromes. To determine whether these drugs affect muscle spindle function, we studied their effect on the resting discharge and on stretch-induced action potential frequencies of proprioceptive afferent neurons.
METHODS
Single unit action potential frequencies of proprioceptive afferents from muscle spindles in the murine extensor digitorum longus muscle of adult C57BL/6J mice were recorded under resting conditions and during ramp-and-hold stretches. Maximal tetanic force of the same muscle after direct stimulation was determined. High-resolution confocal microscopy analysis was performed to determine the distribution of Na 1.4 channels, a potential target for both drugs.
RESULTS
Methocarbamol and mexiletine inhibited the muscle spindle resting discharge in a dose-dependent manner with IC values around 300 μM and 6 μM, respectively. With increasing concentrations of both drugs, the response to stretch was also affected, with the static sensitivity first followed by the dynamic sensitivity. At high concentrations, both drugs completely blocked muscle spindle afferent output. Both drugs also reversibly reduced the specific force of the extensor digitorum longus muscle after tetanic stimulation. Finally, we present evidence for the presence and specific localization of the voltage-gated sodium channel Na 1.4 in intrafusal fibers.
DISCUSSION
In this study we demonstrate that both muscle relaxants affect muscle spindle function, suggesting impaired proprioception as a potential side effect of both drugs. Moreover, our results provide additional evidence of a peripheral activity of methocarbamol and mexiletine.
Topics: Animals; Methocarbamol; Mexiletine; Mice; Mice, Inbred C57BL; Muscle Spindles; Muscle, Skeletal; Neurons, Afferent
PubMed: 35373353
DOI: 10.1002/mus.27546 -
Anatomy and Embryology 1992The literature on the morphology and physiology of the avian muscle spindle is reviewed, with emphasis placed on the period from 1960 to 1991. Traits similar to or... (Review)
Review
The literature on the morphology and physiology of the avian muscle spindle is reviewed, with emphasis placed on the period from 1960 to 1991. Traits similar to or different from mammalian spindles are recognized. Apart from receptors with low intrafusal fiber counts, bird spindles contain two or three types of intrafusal fiber. Unlike that of mammals, the equatorial fiber structure in birds does not lend itself to classification into nuclear bag and nuclear chain types. Avian intrafusal fibers are separable into types based on differences in myosin heavy chain composition and motor innervation, but apportionment of these fiber types to individual spindles is more variable in birds than in mammals. There is morphological evidence in birds for the existence of both gamma and beta innervation; however, confirmation of these systems by physiological experiments is at best sketchy. A general lack of physiological data is currently the greatest drawback to a better understanding of how the avian receptor works, and what role it plays in sensorimotor integration.
Topics: Animals; Birds; Microscopy, Electron; Muscle Spindles; Muscles; Neurons, Afferent; Neurons, Efferent
PubMed: 1387513
DOI: 10.1007/BF00710398 -
ELife Feb 2023The proprioceptive system is essential for the control of coordinated movement, posture, and skeletal integrity. The sense of proprioception is produced in the brain...
The proprioceptive system is essential for the control of coordinated movement, posture, and skeletal integrity. The sense of proprioception is produced in the brain using peripheral sensory input from receptors such as the muscle spindle, which detects changes in the length of skeletal muscles. Despite its importance, the molecular composition of the muscle spindle is largely unknown. In this study, we generated comprehensive transcriptomic and proteomic datasets of the entire muscle spindle isolated from the murine deep masseter muscle. We then associated differentially expressed genes with the various tissues composing the spindle using bioinformatic analysis. Immunostaining verified these predictions, thus establishing new markers for the different spindle tissues. Utilizing these markers, we identified the differentiation stages the spindle capsule cells undergo during development. Together, these findings provide comprehensive molecular characterization of the intact spindle as well as new tools to study its development and function in health and disease.
Topics: Mice; Animals; Muscle Spindles; Multiomics; Proteomics; Muscle, Skeletal; Proprioception
PubMed: 36744866
DOI: 10.7554/eLife.81843 -
The American Journal of Occupational... Aug 1974
Review
Topics: Animals; Central Nervous System; Humans; Mechanoreceptors; Models, Neurological; Muscle Contraction; Muscle Spindles; Neural Pathways; Neurons, Afferent; Neurons, Efferent; Reflex, Stretch; Tendons
PubMed: 4276408
DOI: No ID Found -
Current Opinion in Neurology Oct 2018Muscle spindles are encapsulated mechanosensory receptors within skeletal muscle tissue that inform the central nervous system about the contractile status of each... (Review)
Review
PURPOSE OF REVIEW
Muscle spindles are encapsulated mechanosensory receptors within skeletal muscle tissue that inform the central nervous system about the contractile status of each muscle. This information is required for any coordinated movement and for stable posture. This review summarizes recent findings regarding novel functions for proprioceptive feedback information, muscle spindle disease and the molecular basis of mechanoreception.
RECENT FINDINGS
Muscle spindle function is not limited to regulating motor control but is also required for appropriate realignment of fractured bones, successful regeneration of spinal cord axons after injury and spinal alignment. Several proteins responsible for or modulating mechanotransduction in proprioceptive sensory neurons have been identified, including the Piezo2 channel as a candidate for the principal mechanotransduction channel. Many neuromuscular diseases are known to be accompanied by an impaired function of muscle spindles, resulting in a decline of motor performance and coordination in the patients.
SUMMARY
Our knowledge regarding the molecular basis of muscle spindle function is still incomplete. However, increasing our understanding of mechanotransduction in muscle spindles is a prerequisite for finding appropriate strategies to prevent injuries due to unstable gait and frequent falls.
Topics: Animals; Humans; Mechanoreceptors; Muscle Spindles; Muscle, Skeletal; Proprioception
PubMed: 30095484
DOI: 10.1097/WCO.0000000000000590