[Muscle spindles in the external muscles of the human tongue].
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Humans↗
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Morphology of muscle spindles in the human popliteus muscle. Evidence of a possible monitoring role of the popliteus muscle in the locked knee joint?
The mechanical events leading to locking of the human knee joint are well described in the literature, but there appears to be little information on the source of afferent feedback needed to monitor the locked joint. Human fetal popliteus muscles were studied by histological and graphic reconstruction techniques. The results showed that the muscle contained many muscle spindles. The arrangement of these receptors into complex and tandem forms seems to support the view that the popliteus muscle is capable of subserving kinaesthesia.
Fetus↗
Fusimotor reflexes influencing secondary muscle spindle afferents from flexor and extensor muscles in the hind limb of the cat.
The purpose of this study was to investigate secondary muscle spindle afferents from the triceps-plantaris (GS) and posterior biceps and semitendinosus (PBSt) muscles with respect to their fusimotor reflex control from different types of peripheral nerves and receptors. The activity of single secondary muscle spindle afferents was recorded from dissected and cut dorsal root filaments in alpha-chloralose anaesthetized cats. Both single spindle afferents and sets of simultaneously recorded units (2-3) were investigated. The modulation and mean rate of firing of the afferent response to sinusoidal stretching of the GS and PBSts muscle were determined. Control measurements were performed in the absence of any reflex stimulation, while test measurements were made during reflex stimulation. The reflex stimuli consisted of manually performed movements of the contralateral hind limb, muscle stretches, ligament tractions and electrical stimulations of cutaneous afferents. Altogether 21 secondary spindle afferents were investigated and 20 different reflex stimuli were employed. The general responsiveness (i.e. number of significant reflex effects/number of control-test series) was 52.4%, but a considerable variation between different stimuli was found, with the highest (89.9%) for contralateral whole limb extension and the lowest (25.0%) for stretch of the contralateral GS muscle. The size of the response to a given stimulus varied considerably between different afferents, and, in the same afferent, different reflex stimuli produced effects of varying size. Most responses were characterized by an increase in mean rate of discharge combined with a decrease in modulation, indicative of static fusimotor drive (Cussons et al., 1977). Since the secondary muscle spindle afferents are part of a positive feedback loop, projecting back to both static and dynamic fusimotor neurones (Appelberg Et al., 1892 a, 1983 b; Appelberg et al., 1986), it is suggested that the activity in the loop may work like an amplified which, during some circumstances, enhance the effect of other reflex inputs to the system (Johansson et al., 1991 b).
Afferent Pathways↗
Histochemical study of normal human muscle spindle. Histochemical classification of intrafusal muscle fibers and intrafusal nerve endings.
Normal muscle spindles of human skeletal muscle were studied histochemically. 1) Four histochemical types of intrafusal muscle fibers were classified by ATPase stain: Bag I fiber, Bag II fiber, Chain I fiber and Chain II fiber. Moreover, two types of nuclear bag fibers were classified by NADH Tetrazolium Reductase stain and PAS stain: Bag I fiber and Bag II fiber. 2) Three kinds of fusimotor endings were verified by the cholinesterase technic: en plaque, en grappe and diffuse endings. 3) Two kinds of fusisensory endings were verified by NADH TR stain and also electron-microscopically: primary and secondary sensory endings.
Adenosine Triphosphatases↗
The effects of temporary ischaemia on rat muscle spindles.
Soleus muscle of adult rat is revascularized 5-8 days after sectioning the supplying blood vessels. The temporary ischaemia thus produced results in the rapid concomitant degeneration of extra- and intrafusal muscle fibres along with their nerve terminals and supplying axons. The basal lamina of all muscle fibres usually remains intact throughout the degenerative phase. Necrotic sarcoplasm is removed by phagocytic cells. Satellite cells survive the temporary ischaemia and give rise to presumptive myoblasts which fill the basal-lamina tubes. These myoblasts fuse to form myotubes which, by the 14th day after devascularization, are maturing into muscle fibres in the absence of any innervation. Within the spindle, nuclear-bag fibres degenerate more rapidly than nuclear-chain fibres. Regeneration proceeds more rapidly within the basal-lamina tubes of the original bag fibres than within those of the chain fibres. Reinnervation of regenerating extra- and intrafusal fibres begins 21 days after devascularization and is completed some 7 days later, during which time further equatorial differentiation of some reinnervated intrafusal fibres may occur. Regenerated spindles vary considerably with respect to their innervation and equatorial nucleation. Most contain short, thin, additional muscle fibres as well as those that have regenerated within the basal-lamina tubes of the original fibres.
Animals↗
Effects of changes in preoptic temperature on stretch response of muscle spindle endings in the cat's soleus muscle.
The effects of changing the temperature in the preoptic region on the stretch responses of primary and secondary endings of the muscle spindle in the soleus muscle was investigated in urethane anesthetized cats. The local temperature of the preoptic region was controlled by implanting water perfused thermodes (32-42.5 degrees C). A standard ramp and hold stretch stimulus was repeatedly applied to the soleus muscle during changes of preoptic temperature from normal to hypo- or hyperthermic values. During each stretch the instantaneous firing rate was recorded and the static firing frequency and the dynamic index were electronically determined according to Crowe and Matthews (1964). Of a total of 76 investigated muscle spindle afferents, the stretch responses of 49 (65%) were altered by changing preoptic temperature. The static stretch response was increased in all cases during cooling, whereas during preoptic heating the static stretch response increased in about half of the afferents and decreased in the rest. Increase in the static stretch response during both cooling and heating was usually combined with the appearance of spontaneous discharges at rest. With regard to the static stretch response, primary and secondary muscle spindle endings responded similarly to cooling and heating. Two types of preoptic temperature effects on the stretch responses of primary endings were observed. In the majority of afferents only the static stretch response was augmented during cooling, whereas the peak response was little changed resulting in a decrease of the dynamic index ('static' response type).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Can antidromic stimulation of rat muscle afferents modulate the sensitivity of muscle spindles?
The sensitivity of muscle spindles in gastrocnemius-soleus (GS) muscles following dorsal root (DR) antidromic stimulation (ASt) was investigated in anesthetized rats, in which the hindleg was totally denervated except the GS muscle, ventral roots from L3 to S1 and DRs from L4 to L6, which were severed after laminectomy. The peripheral end of a teased DR filament with single unit tonic discharges from a constantly stretched muscle spindle were recorded and antidromically stimulated after identification. In response to ASt with various frequencies, two different types of ending were found: (1) type I, its tonic discharge was not altered following ASt at 100 Hz for 10 s, while type II was significantly inhibited even at a frequency of 50 Hz; (2) at 300 Hz, both types of endings were inhibited, however, type I recovered in less than 4 s, while type II took more than 15 s to return to control level, and a silent period (1-5 s) was found in type II but not in type I; (3) the effective minimum inhibitory frequency for type I and type II was 200 and 50 Hz, respectively. These results suggest that type I and type II endings may correspond to the primary and the secondary endings of the muscle spindle whose sensitivity may be modulated antidromically by the dorsal root reflex.
Animals↗
The fine structure of denervated and reinnervated muscle spindles: morphometric study of intrafusal muscle fibers.
The fine structure of normal, denervated, and reinnervated muscle spindles in lower lumbrical muscles of rats was studied morphometrically at time intervals ranging from 3-14 months. In control spindles, the mean transverse area of mitochondria was estimated to be more than twice as large in nuclear chain than in typical nuclear bag fibers. Following denervation, there was a severe decrease of the mean number and transverse area of mitochondria, and a moderate, but statistically significant decrease of the mean transverse area of intrafusal muscle fibers (IMFs) despite an increase of the number of IMFs. At 12-14 months of reinnervation, changes of the transverse areas of IMFs were statistically insignificant, but the mean values for the mitochondria were incompletely restored. At 4 x 3 months, after fourfold repeated crush injuries to the nerve, most of the values estimated (transverse area of mitochondria; number, shape, and transverse area of IMFs and nuclei) tended to approach those in denervated rather than in reinnervated IMFs. The differences of the reactions of intra- and extrafusal muscle fibers following complete motor and sensory denervation appeared to be in accordance with their normal dimensional dissimilarities.
Animals↗
Role of nerve and muscle factors in the development of rat muscle spindles.
The soleus muscles of fetal rats were examined by electron microscopy to determine whether the early differentiation of muscle spindles is dependent upon sensory innervation, motor innervation, or both. Simple unencapsulated afferent-muscle contacts were observed on the primary myotubes at 17 and 18 days of gestation. Spindles, encapsulations of muscle fibers innervated by afferents, could be recognized early on day 18 of gestation. The full complement of spindles in the soleus muscle was present at day 19, in the region of the neuromuscular hilum. More afferents innervated spindles at days 18 and 19 of gestation than at subsequent developmental stages, or in adult rats; hence, competition for available myotubes may exist among afferents early in development. Some of the myotubes that gave rise to the first intrafusal (bag2) fiber had been innervated by skeletomotor (alpha) axons prior to their incorporation into spindles. However, encapsulated intrafusal fibers received no motor innervation until fusimotor (gamma) axons innervated spindles 3 days after the arrival of afferents and formation of spindles, at day 20. The second (bag1) intrafusal fiber was already formed when gamma axons arrived. Thus, the assembly of bag1 and bag2 intrafusal fibers occurs in the presence of sensory but not gamma motor innervation. However, transient innervation of future bag2 fibers by alpha axons suggests that both sensory and alpha motor neurons may influence the initial stages of bag2 fiber assembly. The confinement of nascent spindles to a localized region of the developing muscle and the limited number of spindles in developing muscles in spite of an abundance of afferents raise the possibility that afferents interact with a special population of undifferentiated myotubes to form intrafusal fibers.
Animals↗
Observations on the number, distribution and morphological peculiarities of muscle spindles in the tensor tympani and stapedius muscle of man.
Although the middle ear muscles have been described for the first time more than four hundred years ago their role in modulation and transmission of sound is not yet fully understood. Surprisingly very little is known about proprioceptors in these muscles, especially in man, although this seems to be the key to the understanding of their various functions. Therefore, the question for proprioceptive sensory organs in these muscles is still relevant. The tensor tympani and stapedius muscles of four women who had donated their bodies to our institute were taken. Complete serial sections of these muscles were made which were either impregnated with silver, stained with ferric oxide for acidic polysaccharides or incubated with antibodies against S-100 protein. Thereby four to eight (mean five) muscle spindles distributed along the whole muscle could be detected in the tensor tympani muscles. These spindles contain one to three intrafusal muscle fibres and their length ranges from 140 to 4270 microm (mean 1492.8 microm). Furthermore, in three stapedius muscles one to two (mean 1.7) muscle spindles were found. They were from 350 to 500 microm (mean 482 microm) long and contained only one intrafusal muscle fiber. Regarding the diameter of intrafusal muscle fibers in both, the tensor tympani as well as the stapedius muscle, no difference to extrafusal muscle fibers of these muscles could be detected. The structure of these spindles differs considerably from those found in skeletal muscles. The morphological findings presented strongly suggest that muscle spindles occur regularly in both middle ear muscles. The results presented herein are consistent with clinical findings obtained from electromyographic studies and may help to elucidate all functions the middle ear muscles might serve in man.
Aged↗
Muscle spindle distribution, morphology, and density in longus colli and multifidus muscles of the cervical spine.
STUDY DESIGN: Tissue blocks comprising muscle and bone from C5 to C7 segments were harvested at autopsy from 16 individuals ranging in age from 4 to 77 years. The prevertebral longus colli and postvertebral multifidus muscle pairs from one side in each individual were randomly selected for this study of muscle spindles. OBJECTIVES: To determine muscle spindle distribution, morphology, and density for the longus colli and multifidus in caudal segments of the human cervical spine, and to assess whether changes are evident from infancy to old age. SUMMARY OF BACKGROUND DATA: Age-related changes to the osteoligamentous framework of the cervical spine have been well documented. Postural modification accompanies these structural alterations, but there have been limited attempts to document whether muscle sustains a comparable level of morphologic alteration. Previous studies have examined muscle spindles in the neck muscles of various animal models and in a variety of isolated human muscles. However, most of these studies incurred bias through sampling and methodologic assumptions. METHODS: The longus colli and multifidus were resected between C5 and C7, and between left and right pairs selected randomly for spindle analysis. These vertebral segments were selected deliberately because they form the apex of the cervical lordosis and the site at which the greatest age-related modification occurs. The tissue was processed in paraffin, sectioned, and then stained by Masson's trichrome. Spindle characteristics were examined using light microscopy and analyzed by unbiased stereologic methods. A one-sample paired t test was used to ascertain whether the differences in spindle density between the two muscles were statistically significant. RESULTS: The longus colli has a high density of muscle spindles, which appear clustered and concentrated anterolaterally, away from the vertebral body. The multifidus has a low density of muscle spindles, which are found predominantly as single units concentrated closely to the vertebral lamina. No change in spindle distribution, morphology, and density were observed with age. CONCLUSIONS: The current study examined spindle characteristics for an intrinsic neck muscle pair whose coactivation contributes to segmental stability of the cervical spine. The distribution and morphology of muscle spindles differ between the longus colli and the multifidus. In addition, these muscles have significant differences in terms of mean spindle density. Spindle characteristics represent one of many factors that govern proprioceptive regulation in skeletal muscle, and in neck muscles, the central connectivity of these receptors remains undefined. Therefore, although there are anatomic differences between the neck flexor and extensor, the functional implications of these differences are not clear. It is also of interest that spindle characteristics remain unchanged in these intrinsic muscles whose underlying segments are subject to age-related osteoligamentous changes.
Adolescent↗
Histochemical study of long nuclear chain fibers in the cat muscle spindle.
Cat intrafusal muscle fibers were examined histochemically in serial transverse sections of tenuissimus muscle spindles. The "myofibrillar" adenosine triphosphatase staining reaction was used to recognize the nuclear bag and the nuclear chain fibers in 309 spindle poles. Poles of 40 nuclear chain fibers extended for 1,000 micrometer or more beyond the termination of the spindle capsule. These long chain fibers stained less intensely for nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) than the typical chain fibers of shorter polar length. In sections stained for cholinesterases (ChE), the extracapsular regions of most long chain fibers displayed one or two short, dense "plate"-type ChE deposits, which may represent the terminals of skeleto-fusimotor axons. In addition, about one-third of the long chain fibers displayed one or more thinner and smaller areas of ChE activity, possibly corresponding to the endings of fusimotor axons. The overall ChE staining pattern of the typical chain fibers was unlike that of the long chains. However, some of the shorter nuclear chain fibers resembled long chain fibers with the NADH-TR reaction, even though their ChE "plates" were located intracapsularly. It is concluded that nuclear chain fibers in the cat spindle form a class of intrafusal fibers with heterogeneous histochemical properties, and that the long chain fibers represent one fiber subtype.
Adenosine Triphosphatases↗
Branching of muscle spindle afferents of jaw closing muscles in the cat.
1. Functionally isolated single fibres were prepared from the cut central ends of the masseter nerve in cats. Of those firing in response to muscle stretch, most were alpha motor units but some had the properties of afferent fibres innervating muscle receptors. 2. These afferent units were remarkably sensitive to muscle stretch even under anaesthesia deep enough to eliminate all stretch evoked e.m.g. activity in masseter. Moreover, these units responded to gentle pressing of the surface of either the masseter, temporalis or pterygoid muscles. 3. On the basis of their responses to ramp stretch, to high-frequency vibration, to suxamethonium, and to gentle pressing of the muscle surface, the majority were considered to arise from primary or secondary endings of muscle spindles. 4. In reflexly induced jaw movements, the highest discharge frequency of these spindles was observed during the jaw opening phase. However, they were also activated during the jaw closing phase, indicating that the fusimotor innervation to the source spindle was still preserved. 5. From these results, it is concluded that branching of the spindle afferent outside the capsule occurs in the muscle nerve innervating cat's jaw closing muscles.
Action Potentials↗
Reflex patters initiated by the secondary sensory fiber endings of muscle spindles: a proposal.
Muscle spindles have two kinds of sensory fibers, each with stretch-sensitive endings on the nuclear bag muscle fibers and the nuclear chain muscle fibers within the spindle. The stretch reflex responses initiated by the primary sensory fibers have been well defines. There are other stretch reflexes of poorly defined origin and distribution. Clinical studies on spastic patients indicate that these stretch reflexes show regional responses or regional synergies. Stretch of flexor muscles of proximal joints of an extremity causes slowly recruiting, prolonged, reflex flexion in that extremity, in the contralateral extremity and also in the ipsilateral extremity, producing the crossed extension-flexion reflex and long spinal reflex. Likewise, stretch of extensor muscles of the proximal joints initiates a similar extension reflex in the same distribution. Stretch of the distal flexors of an extremity reflexly spreads flexion through that extremity. Stretch of the distal extensors of an extremity spreads extension throughout that extremity. These reflexes can be abolished by intramuscular neurolysis with phenol. They have long internuncial pathways and involve both alpha and gamma motoneurons. The demonstration that these reflex patterns are initiated by stretch of the muscle and show characteristics similar to those shown in physiological studies by the secondary sensory spindle reflexes suggests that they are initiated by stretch of the endings of the secondary sensory fibers of muscle spindles.
Humans↗
Muscle spindles in the human levator veli palatini and palatoglossus muscles.
Muscle spindles are present in many muscles of the speech mechanism including those of the jaw, tongue, larynx, and respiratory system. Past investigations that have examined muscles of the velopharynx for the presence of muscle spindles have reported their existence only in the tensor veli palatini and palatoglossus muscles. The present investigation has demonstrated the existence of muscle spindles in two muscles of the human velopharynx--the levator veli palatini (LVP) and palatoglossus muscles. Seven LVP and two palatoglossus muscles were embedded in paraffin blocks, serially sectioned at 8 microns, and selected slides were stained by a modified Gomori trichrome technique. Scanning by light microscopy at 40x revealed spindles in all of the muscles examined. This positive finding likely reflects the use of a more chromatically distinctive staining procedure and a higher scanning magnification than were used in prior investigations. The potential roles of muscle spindles in velopharyngeal function are addressed.
Humans↗
The location of motor end plates and the distribution and histological structure of muscle spindles in jaw muscles of the rat.
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Animals↗
[Studies of the occurrence, number and individual variations of muscle spindles in the muscles of the human larynx].
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Humans↗
The spindle potential in the frog muscle spindle does not require external Na+.
Spindle potential recorded from the sensory nerve terminal of isolated frog muscle spindles disappeared within 20-30 min after the spindle receptor was perfused with Na+-free (Li, Tris or choline) Ringer's solution, whereas the amplitude of spindle potential was not attenuated for periods up to 60 min when the spindles were perfused in a Na+-free Ringer's solution containing both 10 mM TEA and 0.1 mM 4-aminopyridine after being washed with a normal Ringer's solution containing both the K+-channel blockers. It is concluded that the time-dependent decrease in the amplitude of spindle potential during the application of Na+-free solution is not ascribable to a decrease in the inward current carried by Na+, but is due to an increase in an outward current carried by K+.
Animals↗