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PubMed1984

Ischemic degeneration of the avian muscle spindle.

The neurovascular supply to the pigeon's extensor digitorum communis muscle was disrupted. The muscle spindles were studied by light and electron microscopy to determine whether their degeneration was compatible with regeneration by activation of satellite cells within an intact spindle capsule. The denervation and ischemia induced intrafusal muscle fiber necrosis and degeneration of the sarcolemma and basal lamina. The muscle fibers in the equatorial region were often absent and their sites were indicated by collagenous caps which usually covered the sensory nerve terminal regions. These collagenous caps enclosed amorphous material derived from the intrafusal fibers and degenerating mitochondria from the sensory terminals. In this equatorial region, the basal lamina was present only under the collagenous cap and was disrupted elsewere . The cells of the muscle spindle capsule were more sparse or absent, but the collagen content had increased. The sheath lacked continuity, containing numerous gaps. These observations indicate that the basal lamina does not remain intact, and regeneration may not occur by activation of satellite cells within the former basal lamina, as reported for regenerating rat muscle spindles. This suggests that the mechanisms of regeneration of muscle spindles in rat and pigeon muscle may not be similar.

Animals↗
PubMed1993

An unrelayed projection of jaw-muscle spindle afferents to the cerebellum.

Jaw-muscle spindle afferents were physiologically characterized and stained with horseradish peroxidase. Two types of afferent responses were observed during jaw-muscle stretches; one group showed considerable dynamic sensitivity indicative of primary muscle spindle afferents while the other showed little dynamic responsiveness indicative of secondary spindle afferents. Axon collaterals from both types were observed coursing within the ipsilateral superior cerebellar peduncle, indicating that some jaw-muscle spindle afferents project directly to the cerebellum without relay.

Afferent Pathways↗
PubMed1978

The effect of location of muscle spindle on the predicted reflex control of muscle length.

The location of muscle spindles is such that the length transduced by their end-organs may not represent the total 'origin-to-insertion' length of the muscle. The tendons at least lie in series with the spindles. Using a muscle model based on biceps brachii in man, a length-control senrosystem utilizing feedback either from the total muscle length, or from the 'internal length' of the contractile central region, is modelled on the analog computer. The difference in the nature of the closed-loop regulatory system thus achieved is demonstrated. Anomalous behavior is seen, in that as the length feedback becomes effective the total system response approaches that of a simple mass/spring system in one instance.

Afferent Pathways↗
PubMed1980

Muscle spindles and the regulation of movement.

This paper presents the complexities of muscle spindle structure and function. Experimental evidence indicates that the contribution of muscle spindles to motor control depends upon the cooperation of two distinct systems, one dynamic and one static. The traditional idea that load compensation depends on the segmental stretch reflex action of muscle spindle afferents on alpha motoneurons is questioned and evidence is provided to support the direct dependence of load compensation upon supraspinal centers. Information from muscle spindle afferents allows the nervous system 1) to compare the actual muscle length and velocity of contraction to the desired length and velocity for a particular movement and 2) to compensate for any discrepancies that develop. Segmental pathways from muscle spindle afferents appear to function with Golgi tendon organs to regulate the stiffness or compliance of a muscle.

Afferent Pathways↗
PubMed1981

Muscle spindle autogenetic inhibition in the extraocular muscles of lamb.

The role of extraocular muscle (EOM) proprioceptors on eye motility has been investigated in lambs on "encéphale isolé", by evaluating the tension of EOMs at various lengths and velocities of stretch before and after proprioceptive blocks. The EOM tension, in the absence of proprioceptive input, was higher than in normal conditions. Such an effect occurred at lengthening values greater than 3 mm of stretch from resting muscle length, corresponding to 18 degrees of eye deviation and was dependent on the velocity of the stretch, being more effective at high velocity. The muscle receptors responsible for this effect was determined by comparing the sensitivity to vibratory stimulation of spindles and tendon organs to the amount of inhibition provoked by the same stimulation on an EOM electromyographic activity. The tension inhibition appeared to be correlated to muscle spindle activation. Thus, the presence of muscle spindles can determine a reduction of the tension within the stretched muscles. This result suggests that the EOM length and velocity signals operate moment to moment reduction on the stiffness of the muscle which antagonizes eye displacement, thus facilitating the ocular movements.

Animals↗
PubMed2003

Staining of human thyroarytenoid muscle with myosin antibodies reveals some unique extrafusal fibers, but no muscle spindles.

This study describes the myosin composition of extrafusal and intrafusal muscle fibers found in the human thyroarytenoid (TA) and sternohyoid (control) muscles. We sought to determine the presence of muscle spindles in the TA muscle, and to identify unusual extrafusal fiber types, using the commonly accepted approach of tissue staining with myosin isoform specific antibodies. Extrafusal fibers are organized into motor units, which subsequently produce muscle movement, whereas intrafusal fibers compose muscle spindles, the primary stretch receptor that provides afferent (feed back) information to the nervous system for regulation of motor unit length and tonicity. Immunohistochemical identification of muscle spindles was confirmed in sternohyoid, but not in TA samples; however, some extrafusal fibers contained tonic myosin. These results indicate that human TA muscle functions similar to some mammalian extraocular muscle, performing unloaded (non-weight bearing) contractions without afferent information from native muscle spindles.

Aged↗
PubMed1990

Expression of myosin heavy chain isoforms in developing rat muscle spindles.

The development of muscle spindles, with respect to the expression of myosin heavy chain isoforms was studied in rat hind limbs from 17 days of gestation up to seven days after birth. Serial cross-sections were labelled with antibodies against slow tonic, slow twitch and neonatal isomyosins, myomesin, laminin and neurofilament protein. At 17-18 days of gestation, a small population of primary myotubes expressing slow tonic myosin were identified as the earliest spindle primordia. These myotubes also expressed slow twitch and, to a lesser extent, neonatal myosin. At 19-20 days of gestation a second myotube became apparent; this staining strongly with anti-neonatal myosin. A day later this secondary myotube acquired reactivity to anti-slow tonic and anti-slow twitch myosins. By birth, a third myotube was present; this staining strongly with anti-neonatal myosin but otherwise unreactive with the other antibodies against myosin heavy chains. Three days after birth a fourth myotube, with identical reactivity to the third one, became apparent. Regional variation in the expression of isomyosins, which was present since birth in the two nuclear bag fibers was further enhanced: the nuclear bag staining strongly with anti-slow tonic and antineonatal in the equatorial region and with decreasing intensity towards the poles, whilst with anti-slow twitch the stainability was low in the equatorial and high in the polar region. The nuclear bag fiber showed a homogeneous staining: high with anti-slow tonic, moderate with anti-neonatal, and displayed stainability to anti-slow twitch myosin in the polar regions only. No regional variation was found along the chain fiber/myotube.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Distribution of muscle spindles in the extensor digitorum and hallucis brevis muscles of the macaque as determined by plastination.

The structure-function relationships of the macaque extensor digitorum and hallucis brevis muscle (EDB and EHB), the single intrinsic and four-tendoned muscle of the dorsum of the foot, were investigated in the macaque after preparation of samples by two plastination methods, using gelatin and epoxy resin. These preparative methods clearly revealed the muscle fibers, spindles and myelinated axons in the EDB and EHB. In the more medially located two bellies (the medial two bellies of the EDB), the mean relative proportion of red fibers was larger than in the more laterally located two bellies (the lateral belly of the EDB, and the EHB), while those of intermediate and white fibers were smaller than in the more laterally located two bellies. (The difference was significant between some pairs of bellies.) In the more medially located two bellies, the mean cross-sectional area of each type of fiber, namely, the white, intermediate and red fibers, tended to be smaller than in the more laterally located two bellies. (There were significant differences between many pairs of bellies.) The total number of muscle spindles within an EDB and EHB was 15, and larger numbers of muscle spindles were distributed to the medially located two bellies compared to the laterally located two bellies. (There were significant differences between many pairs of bellies.) These results suggest that the more medially located two bellies of the EDB and EHB are adapted to the relatively precise movements of toes, while the more laterally located two bellies are adapted to the prompt extension and abduction that are related to the arboreal habitat of the macaques.

Animals↗
PubMed1995

Inhibitory effect of sympathetic stimulation on activities of masseter muscle spindles and the jaw jerk reflex in rats.

1. To evaluate sympathetic effects on jaw muscles, the discharges of masseter muscle spindle afferents, jaw muscle electromyographic (EMG) activities and blood flow changes were compared in anaesthetized decerebrate rats before and during electrical stimulation of the cervical sympathetic trunk. 2. To eliminate the possibility of efferent control from the trigeminal motoneurones, muscle spindle activity was recorded from the cut peripheral end of the masseter nerve. The absence of a sympathetic component in the masseter nerve was confirmed by the horseradish peroxidase method. 3. Electrical stimulation of the sympathetic nerve at frequencies within the physiological range reduced muscle spindle afferent discharges evoked by passive jaw opening. 4. Sympathetic stimulation also reduced the EMG activity evoked by the jaw jerk reflex, which may reflect a sympathetic effect on spindle afferents. After cessation of stimulation, a transient increase in EMG activity was observed, which may be due to efferent supply from the trigeminal motoneurones. During rhythmical jaw movements, no sympathetic effect on EMG activity was detected. 5. The above sympathetic effect on muscle spindle afferents and EMG activity was independent of blood flow changes.

Action Potentials↗
PubMed2000

Effects of simulated microgravity on immunoreactivity of conjugated-ubiquitin of muscle spindles of soleus in rats.

It is well known that the muscle spindle is a receptor of muscle's tension and length, it plays an important role in maintaining the muscle's tension. The aim of the present study is to compare the cross-section area (CSA) and the immunoreactivity of conjugated-ubiquitin in soleus extrafusal and intrafusal fibers after simulated-microgravity in order to demonstrate the role of muscle spindle in muscle atrophy induced by simulated microgravity.

Animals↗
PubMed1976

The pathology of the muscle spindle in Duchenne muscular dystrophy.

Muscle spindles have been studied in 7 autopsied cases of Duchenne muscular dystrophy. The autopsies of 2 boys of similar age who died without known neuromuscular disease were used as controls. The abnormalities found consisted of degenerative changes, atrophy and loss of intrafusal muscle fibres, thickening of the spindle capsule and widening of the periaxial space. In some very severely affected muscles there was evidence that spindles were destroyed in the course of the disease. Statistical comparison of these observations was made between the pathological and normal material. The muscle spindle innervation appeared normal in sectioned material. Teased preparations were not available for study.

Adolescent↗
PubMed2004

Age-related changes and the possible adaptability of rat jaw muscle spindles: immunohistochemical and fine structural studies.

Afferent signals from jaw muscle spindles contribute to the feedback mechanism that regulates mastication. The integrity and adaptability of this proprioceptor to age-related changes of the surrounding structures are therefore essential to maintain an appropriate masticatory function throughout life. In this study, we examined muscle spindles obtained from temporal and masseter muscles of 10-week-, 12-, 18-, and 24-month-old Wistar rats, employing immunohistochemistry for protein gene product 9.5 (PGP 9.5) or growth-associated protein (GAP-43) in addition to transmission electron microscopy, in order to investigate their morphological changes in relation to the effect of aging on the adaptive potential of the receptors. Immunohistochemistry for PGP 9.5 showed virtually similar reactions at sensory nerve terminals in all age groups. On the other hand, immunoreactivity for GAP-43 in the sensory nerve ending of the muscle spindles was found 2 and 3 weeks after birth but became almost undetectable by 10 weeks. However GAP-43 immunoreactions occasionally reappeared in those of spindles in 12- and 18-month old animals, and vanished again by 24 months of age. Electron microscopic observations also revealed age-related morphological changes in the intrafusal muscle fibers of the rats in 12-month and older groups. The extent of degenerative and/or atrophic alterations of intrafusal fibers increased with age and involved the nerve elements of spindles by 24 months. These findings indicate that the adaptation potential of rat jaw muscle spindles is well preserved until middle age, but diminishes in elderly animals. Structural changes of muscle spindles in elderly animals probably contribute to the deterioration of the muscular function.

Age Factors↗
PubMed1980

[Electron microscopic study on muscle spindles in poliomyelitis (author's transl)].

The ultrastructures of the fifteen muscle spindles in poliomyelitis were studied especially concerning the structural alterations of intrafusal muscle fibers, sensory and motor nerve endings, though light microscopically previous workers have yielded no significant findings. Simultaneously performed light microscopic study of the same specimens revealed degenerative changes of the capsules in four muscle spindles and less significant changes in the remaining eleven muscle spindles. Ultrastructural findings of intrafusal muscle fibers consist or small vacuoles with irregular loss of myofilaments. Electron density of mitochondria in sensory nerve endings have increased and its cristae have disappeared. Plasma membranes of sensory nerve endings and intrafusal fibers are discontinuous. Mitochondria in motor nerve endings showed same findings, and basal lamina and junctional folds are also discontinuous or partially obscure. These findings seem to be neuropathic alterations of muscle spindles in poliomyelitis.

Adolescent↗
PubMed1980

Muscle spindle function in organophosphorus neuropathy.

The contribution of muscle spindle dysfunction to the neurological signs o-delayed organophosphorus neuropathy was investigated in the hindlimbs of cats intra-arterially injected with 2 mg/kg of diisopropylfluorophosphate (DFP). In this model of a delayed peripheral neuropathy, the animals exhibit a peculiar high-step gait and a sluggish response to noxious stimuli. These signs initially appear 14 days and are maximum 21--28 days after DFP administration. The position sensitivities of secondary but not primary soleus muscle spindles were depressed at 14 days after DFP. At 21 days after DFP, both primary and secondary endings had attenuated position sensitivities and significantly elevated thresholds. Spindle function was normal at 56 days after DFP exposure. The onset, peak and recovery of soleus muscle spindle dysfunction corresponded to those in alpha-motor axons, indicating the mixed sensory motor nature of organophosphorus neuropathy. Thus, impairment of both sensory and motor functions contributes to the neurological signs of this neuropathy.

Afferent Pathways↗