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Scientific Reports Feb 2023Across the human body, skeletal muscles have a broad range of biomechanical roles that employ complex proprioceptive control strategies to successfully execute a desired...
Across the human body, skeletal muscles have a broad range of biomechanical roles that employ complex proprioceptive control strategies to successfully execute a desired movement. This information is derived from peripherally located sensory apparatus, the muscle spindle and Golgi tendon organs. The abundance of these sensory organs, particularly muscle spindles, is known to differ considerably across individual muscles. Here we present a comprehensive data set of 119 muscles across the human body including architectural properties (muscle fibre length, mass, pennation angle and physiological cross-sectional area) and statistically test their relationships with absolute spindle number and relative spindle abundance (the residual value of the linear regression of the log-transformed spindle number and muscle mass). These data highlight a significant positive relationship between muscle spindle number and fibre length, emphasising the importance of fibre length as an input into the central nervous system. However, there appears to be no relationship between muscles architecturally optimised to function as displacement specialists and their provision of muscle spindles. Additionally, while there appears to be regional differences in muscle spindle abundance, independent of muscle mass and fibre length, our data provide no support for the hypothesis that muscle spindle abundance is related to anatomical specialisation.
Topics: Humans; Muscle Spindles; Muscle, Skeletal; Mechanoreceptors; Proprioception; Movement
PubMed: 36806712
DOI: 10.1038/s41598-023-30044-w -
Sheng Li Xue Bao : [Acta Physiologica... Dec 2022Muscle spindle is the key proprioceptor in skeletal muscles and plays important roles in many physiological activities, such as maintaining posture, regulating movement... (Review)
Review
Muscle spindle is the key proprioceptor in skeletal muscles and plays important roles in many physiological activities, such as maintaining posture, regulating movement and controlling speed variation. It has significant clinical relevance and is emerging as a promising therapeutic target for the treatment of motor functional impairment and metabolic diseases. In this review, we summarized muscle spindle distribution and the mechanism of mechanical signal transmission, and reviewed the research progress on morphological and structural characteristics of muscle spindles.
Topics: Muscle Spindles; Muscle, Skeletal; Clinical Relevance
PubMed: 36594392
DOI: No ID Found -
Sleep Aug 2022We evaluated common marmosets as a perspective animal model to study human sleep and wake states.
STUDY OBJECTIVES
We evaluated common marmosets as a perspective animal model to study human sleep and wake states.
METHODS
Using wireless neurologger recordings, we performed longitudinal multichannel local field potential (LFP) cortical, hippocampal, neck muscle, and video recordings in three freely behaving marmosets. The brain states were formally identified using self-organizing maps.
RESULTS
Marmosets were generally awake during the day with occasional 1-2 naps, and they slept during the night. Major electrographic patterns fall in five clearly distinguished categories: wakefulness, drowsiness, light and deep NREM sleep, and REM. Marmosets typically had 14-16 sleep cycles per night, with either gradually increasing or relatively low, but stable delta power within the cycle. Overall, the delta power decreased throughout the night sleep. Marmosets demonstrated prominent high amplitude somatosensory mu-rhythm (10-15 Hz), accompanied with neocortical ripples, and alternated with occipital alpha rhythm (10-15 Hz). NREM sleep was characterized with the presence of high amplitude slow waves, sleep spindles and ripples in neocortex, and sharp-wave-ripple complexes in CA1. Light and deep stages differed in levels of delta and sigma power and muscle tone. REM sleep was defined with low muscle tone and activated LFP with predominant beta-activity and rare spindle-like or mu-like events.
CONCLUSIONS
Multiple features of sleep-wake state distribution and electrographic patterns associated with behavioral states in marmosets closely match human states, although marmoset have shorter sleep cycles. This demonstrates that marmosets represent an excellent model to study origin of human electrographical rhythms and brain states.
Topics: Animals; Callithrix; Electroencephalography; Humans; Neocortex; Sleep; Sleep, REM; Wakefulness
PubMed: 35576961
DOI: 10.1093/sleep/zsac106 -
Experimental Physiology Jan 2024Muscle spindles encode mechanosensory information by mechanisms that remain only partially understood. Their complexity is expressed in mounting evidence of various... (Review)
Review
Muscle spindles encode mechanosensory information by mechanisms that remain only partially understood. Their complexity is expressed in mounting evidence of various molecular mechanisms that play essential roles in muscle mechanics, mechanotransduction and intrinsic modulation of muscle spindle firing behaviour. Biophysical modelling provides a tractable approach to achieve more comprehensive mechanistic understanding of such complex systems that would be difficult/impossible by more traditional, reductionist means. Our objective here was to construct the first integrative biophysical model of muscle spindle firing. We leveraged current knowledge of muscle spindle neuroanatomy and in vivo electrophysiology to develop and validate a biophysical model that reproduces key in vivo muscle spindle encoding characteristics. Crucially, to our knowledge, this is the first computational model of mammalian muscle spindle that integrates the asymmetric distribution of known voltage-gated ion channels (VGCs) with neuronal architecture to generate realistic firing profiles, both of which seem likely to be of great biophysical importance. Results predict that particular features of neuronal architecture regulate specific characteristics of Ia encoding. Computational simulations also predict that the asymmetric distribution and ratios of VGCs is a complementary and, in some instances, orthogonal means to regulate Ia encoding. These results generate testable hypotheses and highlight the integral role of peripheral neuronal structure and ion channel composition and distribution in somatosensory signalling.
Topics: Animals; Muscle Spindles; Mechanotransduction, Cellular; Neurons; Ion Channels; Electrophysiological Phenomena; Mammals
PubMed: 36966478
DOI: 10.1113/EP091099 -
Experimental Brain Research Oct 2019This is an account of experiments carried out in my laboratory over more than 20 years, exploring the influence of exercise on human limb position sense. It is known... (Review)
Review
This is an account of experiments carried out in my laboratory over more than 20 years, exploring the influence of exercise on human limb position sense. It is known that after intense exercise we are clumsy in the execution of skilled movements. The first question we posed concerned eccentric exercise, where the contracting muscle is forcibly lengthened. Such exercise produces muscle damage, and the damage might extend to the muscle's proprioceptors, the muscle spindles, producing a disturbance of limb position sense. However, provided the exercise was sufficiently severe (20-30% fall in muscle force), comparing eccentric exercise with concentric exercise, where no damage ensues, there was no difference in the effects on position sense. After exercise of elbow muscles, the forearm was always perceived as more extended than its actual position. It led to a new hypothesis: after exercise, did the extra effort required to lift the fatigued arm provide a position signal? Findings based on spindles' thixotropic behaviour did not support such a proposition for the elbow joint, although at the wrist an effort signal may contribute. Spindle thixotropy has also been proposed to explain the poor proprioception experienced under conditions of weightlessness. After exercise of elbow extensors or flexors, the position errors were always in the direction of forearm extension. At the knee, after exercise the lower leg was always perceived as more flexed. These findings led to the conclusion that disturbances to position sense, post-exercise, did not involve peripheral receptors, and that the effect arose within the brain.
Topics: Exercise; Fatigue; Humans; Muscle Contraction; Muscle Spindles; Muscle, Skeletal; Proprioception; Retrospective Studies
PubMed: 31471677
DOI: 10.1007/s00221-019-05634-8 -
BMJ Neurology Open 2023Muscle membranes have a sensation of pain, but within the muscle tissue, the origin of pain is unclear. We present a hypothesis that the pain receptors of the muscle...
BACKGROUND
Muscle membranes have a sensation of pain, but within the muscle tissue, the origin of pain is unclear. We present a hypothesis that the pain receptors of the muscle tissue are situated principally in the muscle spindles. A recent report reintroduced that 'end plate spikes' in needle electromyography (EMG) are fusimotor unit potentials of the intrafusal muscle fibres, and thus represent a marker of muscle spindles.
METHODS
We studied four relaxed muscles with 50 EMG needle insertions in each and mapped the appearance of pain and spontaneous EMG activity.
RESULTS
Only 4.0% of the needle insertions in muscle tissue elicited pain. However, needle insertions in local active points showing 'end plate spikes' and, thus, fusimotor unit potentials of the muscle spindles elicited pain in 86% of the insertions, whereas needle insertions in points without 'end plate spikes' elicited pain in only 1.0% of the insertions (p<0.001).
CONCLUSIONS
Muscle spindles have pain receptors. The extrafusal muscle tissue is practically pain-free for the needle insertions. This demonstrates a scarcity of extrafusal pain receptors. How this observation is put into perspective with the muscle pain syndromes was discussed.
PubMed: 37337530
DOI: 10.1136/bmjno-2023-000420 -
Anatomical Record (Hoboken, N.J. : 2007) Oct 2023Muscle spindles are sensory receptors in skeletal muscle that provide information on muscle length and velocity of contraction. Previous studies noted that facial...
Muscle spindles are sensory receptors in skeletal muscle that provide information on muscle length and velocity of contraction. Previous studies noted that facial muscles lack muscle spindles, but recent reports indicate that the human platysma muscle and "buccal" muscles contain spindles. Mammalian facial muscles are active in social communication, vibrissa movement, and vocalizations, including human speech. Given these functions, we hypothesized that facial muscles contain muscle spindles, and we predicted that humans would have the greatest number, given the role our lips play in speech. We examined previously sectioned and stained (with H&E and trichrome stains) orbicularis oris (upper fibers) and zygomaticus (major) muscles across a broad phylogenetic range of mammalian species, spanning a wide distribution of body size and ecological niche, to assess the presence of muscle spindles. We also stained several sections with Sirius red to highlight the muscle spindle capsule. Our results indicate that mammalian facial muscles contain muscle spindles, supporting our hypothesis. Contrary to our prediction, though, humans (and other primates) had the lowest number of muscle spindles. We instead found that the carnivoran sample and the horse sample had the greatest number of spindles. Larger body size and nocturnality were also associated with a greater number of spindles. These results must be viewed with caution, though, as our sample size was small and there are critical mammalian taxa missing. Future work should use an expanded phylogenetic range of mammalian species to ascertain the role that phylogeny plays in muscle spindle presence and count.
Topics: Humans; Animals; Horses; Facial Muscles; Muscle Spindles; Phylogeny; Muscle, Skeletal; Mammals
PubMed: 36799659
DOI: 10.1002/ar.25172 -
Neurological Sciences : Official... Sep 2021Focal hand dystonia (FHD) is usually adult-onset focal dystonia that can be associated with marked occupational and functional disability leading to reduced quality of... (Review)
Review
BACKGROUND
Focal hand dystonia (FHD) is usually adult-onset focal dystonia that can be associated with marked occupational and functional disability leading to reduced quality of life.
METHODS
Relevant studies on treatment options for FHD, their limitations, and current recommendations were reviewed using the PubMed search until March 31, 2021. Besides, the reference lists of the retrieved publications were manually searched to explore other relevant studies.
RESULTS
and conclusion Currently, botulinum toxin has the best evidence for treatment of FHD, and 20-90% of patients experience symptomatic improvement. However, its benefit is often limited by the reduction of muscle tonus acting on the muscle spindle. Different surgical modalities that have been used to treat focal hand dystonia include lesional surgery, deep brain stimulation, and magnetic resonance-guided focused ultrasound thalamotomy. Recent studies exploring the role of behavioral techniques, sensorimotor training, and neuromodulation for the treatment of focal hand dystonia have reported good outcomes, but larger studies are required before implementing these interventions in practice.
Topics: Adult; Botulinum Toxins; Dystonic Disorders; Humans; Magnetic Resonance Imaging; Quality of Life
PubMed: 34213695
DOI: 10.1007/s10072-021-05432-7 -
Current Opinion in Neurobiology Jun 2022The muscle spindle (MS) provides essential sensory information for motor control and proprioception. The Group Ia and II MS afferents are low threshold slowly-adapting... (Review)
Review
The muscle spindle (MS) provides essential sensory information for motor control and proprioception. The Group Ia and II MS afferents are low threshold slowly-adapting mechanoreceptors and report both static muscle length and dynamic muscle movement information. The exact molecular mechanism by which MS afferents transduce muscle movement into action potentials is incompletely understood. This short review will discuss recent evidence suggesting that PIEZO2 is an essential mechanically sensitive ion channel in MS afferents and that vesicle-released glutamate contributes to maintaining afferent excitability during the static phase of stretch. Other mechanically gated ion channels, voltage-gated sodium channels, other ion channels, regulatory proteins, and interactions with the intrafusal fibers are also important for MS afferent mechanosensation. Future studies are needed to fully understand mechanosensation in the MS and whether different complements of molecular mediators contribute to the different response properties of Group Ia and II afferents.
Topics: Action Potentials; Ion Channels; Mechanoreceptors; Muscle Spindles; Neurons, Afferent; Proprioception
PubMed: 35430481
DOI: 10.1016/j.conb.2022.102542