Stretch receptors in urodele limb muscles

Summary Non-encapsulated, fine beaded nerve endings were found histologically on some muscle fibres in a number of limb muscles in newts and axolotls. They were present in newt muscles that had been chronically de-efferented, and in which no efferent activity survived, and were therefore likely to be sensory. They were located only on muscle fibres on or near the outside surface of the muscle. These small-diameter muscle fibres were characterised histochemically by low lipid, SDH and phosphorylase content; ultrastructurally by low glycogen content, and relatively large myofilaments poorly delimited by a sparse SR. There were many of this type (Type 1) that did not support sensory endings. A few endings occurred on another larger-diameter type of fibre (Type 2) whose properties were opposite to those listed above for Type 1. There was virtually no specialization of muscle fibre structure beneath the sensory endings.Physiological experiments involving ramp-and-hold and sinusoidal stretch applied to the muscle whilst recording single-unit afferent responses in m.ext. dig. III of axolotls showed unit responses very similar to those known from muscle spindles, particularly those of the frog.We are grateful to the M.R.C. for an equipment grant (to R.M.A.P.R.), and to Mrs. Janis Taberner for her technical help. Part of this work was done during the tenure of a Nuffield-NRC Lectureship (Q.B.) which is gratefully acknowledged, as is financial support by Prof. J.R. Nussall during a visit to the University of Alberta at Edmonton.     

Motor and sensory reinnervation of fast and slow mammalian muscles

Summary 1. The formation of endplates outside the original endplate region of a muscle fibre was studied in slow and fast rat muscles. It was found that such new endplates are readily formed on the soleus muscle, whereas hardly at all in the fast extensor digitorum longus. Most new endplates appear to be morphologically normal within 2 months after nerve implantation.2. The time course of recovery of slow and fast cat muscles was followed after crushing the sciatic nerve. It was found that the slow soleus muscle recovers more rapidly than the fast flexor hallucis longus muscle.3. The endplates of reinnervated cat muscles are more complicated than those of the control muscles, but have nevertheless fewer nerve terminals per endplate. Reinnervated muscles are more sensitive to curare and it is suggested that this is due to a decrease in transmitter release, for it was found that less acetylcholine is released from reinnervated rat hemidiaphragms than from control ones.4. Motor and sensory reinnervation of spindles and tendon organs was studied. At the time when motor reinnervation is almost completed the sensory endings from spindles and tendon organs are highly abnormal. Thus sensory reinnervation proceeds much more slowly than motor.     

Palisade endings and proprioception in extraocular muscles: a comparison with skeletal muscles

This article describes current views on motor and sensory control of extraocular muscles (EOMs) based on anatomical data. The special morphology of EOMs, including their motor innervation, is described in comparison to classical skeletal limb and trunk muscles. The presence of proprioceptive organs is reviewed with emphasis on the palisade endings (PEs), which are unique to EOMs, but the function of which is still debated. In consideration of the current new anatomical data about the location of cell bodies of PEs, a hypothesis on the function of PEs in EOMs and the multiply innervated muscle fibres they are attached to is put forward.     

Origin of myoblasts involved in the formation of the flight muscles of a butterfly (Pieris brassicae)

The larval muscle precursors of the dorsal longitudinal flight muscles of Pieris brassicae were examined by electron microscopy at five developmental stages of the fifth larval instar. At the beginning of this instar, a large neuromuscular area (NMA) was observed along the larval muscle precursors, on the side of the muscle where the nerve comes into contact with it. This area was delimited by the basement membrane of the muscle and by a thicker external basal lamina and contained nerve branches, tracheae, neuromuscular endings and cells with a cytoplasm rich is free ribosomes. Cells similar to the ribosome rich cells of the NMA were located along the motor nerves supplying the larval muscle precursors in a compartment joined to the NMA. From 78 hr after the fourth moult onwards, the ribosome-rich cells increased in number, accumulated inside the NMA and in the space around the nerves. Then they penetrated the muscle fibre via the channels of the transverse system. These cells were the myoblasts that later help to form the flight muscles. As regards their earlier origin, they do not seem to derive from cells formed from larval fibre nuclei, but might be present together with the muscle precursors, and along the nerves from the beginning of larval development. The differences with the Nematoceran Diptera are discussed.     

Identification of Different Types of Spinal Afferent Nerve Endings That Encode Noxious and Innocuous Stimuli in the Large Intestine Using a Novel Anterograde Tracing Technique

In mammals, sensory stimuli in visceral organs, including those that underlie pain perception, are detected by spinal afferent neurons, whose cell bodies lie in dorsal root ganglia (DRG). One of the major challenges in visceral organs has been how to identify the different types of nerve endings of spinal afferents that transduce sensory stimuli into action potentials. The reason why spinal afferent nerve endings have been so challenging to identify is because no techniques have been available, until now, that can selectively label only spinal afferents, in high resolution. We have utilized an anterograde tracing technique, recently developed in our laboratory, which facilitates selective labeling of only spinal afferent axons and their nerve endings in visceral organs. Mice were anesthetized, lumbosacral DRGs surgically exposed, then injected with dextran-amine. Seven days post-surgery, the large intestine was removed. The characteristics of thirteen types of spinal afferent nerve endings were identified in detail. The greatest proportion of nerve endings was in submucosa (32%), circular muscle (25%) and myenteric ganglia (22%). Two morphologically distinct classes innervated myenteric ganglia. These were most commonly a novel class of intraganglionic varicose endings (IGVEs) and occasionally rectal intraganglionic laminar endings (rIGLEs). Three distinct classes of varicose nerve endings were found to innervate the submucosa and circular muscle, while one class innervated internodal strands, blood vessels, crypts of lieberkuhn, the mucosa and the longitudinal muscle. Distinct populations of sensory endings were CGRP-positive. We present the first complete characterization of the different types of spinal afferent nerve endings in a mammalian visceral organ. The findings reveal an unexpectedly complex array of different types of primary afferent endings that innervate specific layers of the large intestine. Some of the novel classes of nerve endings identified must underlie the transduction of noxious and/or innocuous stimuli from the large intestine.     

Effects of Latrodectus spider venoms on sensory and motor nerve terminals of muscle spindles

The effects of the venoms of the spiders Latrodectus mactans tredecimguttatus (black widow) and Latrodectus mactans hasselti (red back) on sensory nerve terminals in muscle spindles were studied in the mouse. A sublethal dose of venom was injected into tibialis anterior and extensor digitorum longus muscles of one leg. After survival from 30 minutes to 6 weeks muscles were examined in serial paraffin sections impregnated with silver or by electron microscopy. Sensory endings became swollen, some within 30 minutes, while over the next few hours there was progressive degeneration of annulospiral endings. By 24 hours every spindle identified by light or electron microscopy was devoid of sensory terminals. Degenerated nerve endings were taken up into the sarcoplasm of intrafusal muscle fibres. Regeneration of sensory axons began within 24 hours, new incomplete spirals were formed by 5 days and by 1 week annulospiral endings were almost all normal in appearance. Intrafusal motor terminals underwent similar acute degenerative and regenerative changes. These experiments show that intrafusal sensory and motor terminals are equally affected by Latrodectus venoms. Sensory nerve fibres possess a capacity for regeneration equal to that of motor fibres and reinnervate intrafusal muscle fibres close to their original sites of innervation.     

猕猴声带肌运动神经终末特点的研究

本文通过银法对猕猴声带肌运动神经终末和运动终板的形态进行了观察。发现声带肌与四肢肌不同，除肌纤维纤细，排列不甚紧密度，其神经支配比较丰富，运动终板数目较多，形态多姿。本观察对研究各种动物声带肌的运动神经终末特点提供比较解剖学资料。     

Experimental studies on the afferent innervation of the cricothyroid muscle in dogs

The cricothyroid muscle in dogs received branches from two independent nerves, namely the external ramus of the cranial laryngeal nerve and the pharyngeal branch of the vagus. Classical spindles are infrequent in the muscle. Atypical forms of sensory endings were identified. Two end-plates were frequently met with on a single extrafusal fibre. Sectioning of the external ramus of the cranial laryngeal nerve was followed by degeneration of spindles. Intact axons detected up to 6 months after operation are probably derived from the pharyngeal branch of the vagus. Chromatolytic changes occurred in the ipsilateral dorsal vagal nucleus and the capsulated ganglion at the entry of the nerve into the muscle. Chromatolysis occurred in the intramuscular ganglion cell rows and in neurons of the ipsilateral nodose ganglion. Morphological alterations were more pronounced in the ipsilateral medial column of the nucleus ambiguus. No changes were observed in the somata of the mesencephalic nucleus.     

Terrapin muscle afferents studied by cord dorsum potential analyses

Rostro-caudal ramification of terrapin hindlimb afferent nerves have been studied by cord dorsum potential analyses. Stimulation of muscle and cutaneous nerves evoke different waveforms, related to the difference in fibre diameter spectra. Afferents of small muscles enter the cord through one spinal nerve, while afferents of large muscles are connected to the cord by up to four spinal roots. In their entrance segment muscle afferents bifurcate into branches extending in rostral and caudal direction over at least three segments.     

Studies on the distribution of calcitonin gene-related peptide-like and substance P-like immunoreactivities in rat hind limb muscles

Summary The tibialis anterior, extensor digitorum longus and soleus muscles in the rat were examined with respect to the presence of calcitonin gene-related peptide-like as well as substance P-like immunoreactivity. In some of the motor endplates in these muscles, identified by staining for acetylcholinesterase activity, calcitonin gene-related peptide-like immunoreactivity was detected, but in others it was not. Calcitonin gene-related peptide-like immunoreactivity was found to coexist with substance-P-like immunoreactivity in nerve fibres located outside and inside the capsule of the muscle spindles, as well as in nerve fibres located in nerve fascicles. These fibres presumably represent sensory nerve fibres. Calcitonin gene-related peptide-like immunoreactivity, but not substance P-like immunoreactivity, was also detected, in cap-like structures located on the surface of the intrafusal muscle fibres in the polar regions of the spindles, structures which are likely to correspond to motor plate endings. The observations suggest that calcitonin gene-related peptide is heterogeneously present in the endplates of rat hind limb muscles, and gives for the first time immunohistochemical evidence for the presence of calcitonin gene-related peptide and substance P in the innervation of muscle spindles.     

Morphological study of nerve endings in jaw muscles of post-hatching American alligators (Alligator mississippiensis)

Two months after hatching, the fibers of the jaw muscles of the American alligator are associated with three types of nerve terminals namely, plates, simple plates, and grape endings. Simple plate endings are mainly observed on the small muscle fibers. Grape-type endings are found on muscle fibers that resemble the tonic fibers of garter snakes (Hess, Am. J. Anat., '63). Most terminals are plate endings and account for 53.7–74.7% of terminals per muscle. Fibers with grape-type endings were found in all the jaw muscles studied; they lack well organized T-systems, M-lines, and post-junctional sarcolemmal folds, as well as irregularly distributed small of fibrils, and zigzag Z-lines. The properties of nerve endings of the American alligator indicate that M. depressor mandibulae, M. pseudotemporalis, and M. pterygoideus posterior have primary roles in jaw movements. M. pterygoideus anterior and M. intramandibularis contribute mainly to postural adjustments of the jaws. The multiplicity of nerve terminals in the jaw muscles of American alligators contrasts with the simple movements of their jaws. © 1994 Wiley-Liss, Inc.     

Neuromuscular spindles of the extrinsic ocular musculature of the moufflon

Proprioceptive innervation of moufflon extrinsic ocular musculature and m. levator palpebrae superioris was studied. Muscle spindles and Golgi tendon organs were found. The first ones are usually between 1st and 2nd order muscle fascicles. The muscle spindles are highly represented in the extrinsic ocular muscles, but less numerous in m. levator palpebrae superioris. Their number varies according to muscles and individuals. In the same subject, also the ratio between the number of the muscle spindles found in m. rectus dorsalis and that of m. levator palpebrae superioris was examined. Besides, the histological structure of the intrafusal fascicles was investigated. Particular attention was devoted to the nerve supply of the muscle spindle. By means of impregnating methods, sensory and motor endings were identified. Primary and secondary sensory endings only in a few cases showed their usual pattern: motor fibres can end in form of plates or trails. Golgi tendon organs were observed between the tendon and the muscular tissue and are always less numerous.     

The fate of specific motoneurons and sensory neurons of the pregenital abdominal segments inTenebrio molitor (Insecta : Coleoptera) during metamorphosis

The anatomy and innervation of the lateral external muscle and sensory cells located in the ventral region of pregenital abdominal segments were examined at the larval and adult stages ofTenebrio molitor (Coleoptera). All seven muscles located in this region degenerate during the pupal stage, whilst only the lateral external median (lem) appears in the adult. Backfillings of the motor nerve innervating this muscle reveal that, at both larval and adult stages, it is innervated by ten neurons. Intracellular records from the muscle fibres show that two neurons are inhibitory, and at least five are excitatory. There are also two unpaired neurons. A variety of sensory organs are located in the ventral region of the larvae, whilst only campaniform sensilla are found in the adult. At both stages, the innervation pattern of the sensory nerve branches is very similar. Also, the central projections of the sensory cells occupy similar neuropilar areas. Finally, prolonged intracellular records from the lem muscle revealed that, at the larval stage, it participates only in segmental or intersegmental reflexes, whilst in the adult it has a primary expiratory role in ventilation. The results show that extensive changes occur in the number of muscles located in the ventral region of the pregenital abdominal segments, as well as in the arrangement and number of sensory neurons, in the structure of the exoskeleton, and even in the central nervous system. In contrast, only minor changes are observed in the sensory and motor nerve branches, in the sensory projections, and in the number and the location of the motoneurons innervating the lateral external median muscle. Correspondence to: G. Theophilidis     

Ultrastructural abnormalities of muscle spindles in the rat masseter muscle with malocclusion-induced damage

Human temporomandibular disorders due to disturbed occlusal mechanics are characterized by sensory, motor and autonomic symptoms, possibly related to muscle overwork and fatigue. Our previous study in rats with experimentally-induced malocclusion due to unilateral molar cusp amputation showed that the ipsilateral masseter muscles undergo morphological and biochemical changes consistent with muscle hypercontraction and ischemia. In the present study, the masseter muscle spindles of the same malocclusion-bearing rats were examined by electron microscopy. Sham-operated rats were used as controls. In the treated rats, clear-cut alterations of the muscle spindles were observed 26 days after surgery, when the extrafusal muscle showed the more severe damage. The fusal alterations affected predominantly capsular cells, intrafusal muscle fibers and sensory nerve endings. These results suggest that in the malocclusion-bearing rats, an abnormal reflex regulation of the motor activity of the masticatory muscles may take place. They also allow us to hypothesize that muscle spindle alterations might be involved in the pathogenesis of human temporomandibular disorders.     

Functional properties of interneurons of the masticatory reflex

Interneurons of the supratrigeminal nucleus, transmitting effects from the sensory and motor branches of the trigeminal nerve to motoneurons of the muscles of mastication were investigated. Two groups of interneurons with different functional connections were found. The first group (A) contains neurons excited during stimulation of the sensory branches and the motor nerve to the digastric muscle (A₁), neurons excited during stimulation of sensory branches and high-threshold afferents of the motor nerve to the masseter muscle (A₂), and neurons excited only by low-threshold afferents of the motor nerve to the masseter muscle (A₃). Neurons of the second group (B) were activated only by sensory fibers of the trigeminal nerve. It is postulated that interneurons of group A transmit inhibitory effects to motoneurons of antagonist muscles of the lower jaw. Group B interneurons participate in the transmission of excitatory influences to motoneurons of the digastric muscle.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 150–157, March–April, 1972.     

大鼠食管胸段，腹段乙酰胆碱酯酶阳性神经的配布

大鼠食管胸段和腹段壁内乙酰胆碱酯酶（ＡＣｈＥ）阳性神经存在于神经束和分支的粗细神经纤维内,也见于外膜丛,肌间丛,粘膜下丛和粘膜肌内。食管肌层内ＡＣｈＥ阳性神经纤维多而密集,而食管腹段肌内尤为丰富,肌间神经纤维末梢分布于肌束表面,可能与控制肌纤维活动有关;分布于肌内,粘膜下层和上皮基部的ＡＣｈＥ阳性神经中,尚含有内脏感觉神经纤维。食管壁的肌间丛和粘膜下丛内散在有多极形和卵园形的ＡＣｈＥ阳性神经元,在食管腹段内数多,而以中小型神经元为主。     

Ultrastructure of the joint receptors in the frog (Rana temporaria).

The ultrastructure of sensory nerve endings was examined in joint capsules of large limb joints in three adult frogs (Rana temporaria). The joint receptors are represented by the only one kind of sensory nerve endings--by free nerve endings. The unmyelinized preterminal desintegrates into single terminals. This branching is bound on the most peripheral cell of the Schwann cell by means of mesaxons, they pass from the pericaryum of the Schwann cell peripherally. The branches of the nerve terminal are surrounded by a cover of 1...3 cytoplasmatic processes of the Schwann cell. The surface lamella is covered by a distinct basal membrane. Bundles of collagenous fibrils pass along the branches of the nerve terminal. Quite naked nerve endings were not observed. The axoplasma of the nerve terminal contains strikingly few cell organels. Besides axially passing neurofilaments and neurotubules only sporadic mitochondria and clear vesicles were observed. The accumulation of mitochondria, characteristic for the axoplasma of nerve terminals, was observed in no case. Free nerve endings which were found in the joint capsules of the frog belong among so called "free penicillate nerve endings".     

Dynamic mechanism of visual accommodation in teleosts: structure of the lens muscle and its nerve control

The accommodatory system was examined in two teleosts (mackerel and bass). The fine structure and innervation of the lens muscle is presented to characterize the muscle organization. The neural pathway involved in the dynamic accommodation was examined by analysing the fibre spectrum of the ciliary nerve, and the nerve that controls the lens-muscle activity was studied by means of electrical stimulation. The lens muscle is composed of smooth-muscle cells, which contain numerous mitochondria. Many synaptic endings are also found on the muscle cells; these synaptic endings contain many agranular vesicles. From the results of the fibre analysis, it was found that the nerve that controls the lens muscle contains less than 100 myelinated nerve fibres in both fish: the electrical stimulation experiments demonstrate that the muscle is controlled by oculomotor (parasympathetic) nerve fibres. Ultrastructural features of the lens muscle and its nerve control resemble those of the mammalian ciliary muscle. The teleostean lens muscle is classified as a multi-unit smooth muscle.     

The Fine Structure of Muscle Spindles in the Lumbrical Muscles of the Rat

Lumbrical muscles of young rats were fixed with OsO₄ and embedded in methacrylate for electron microscopy. The spindle capsule was found to be continuous with and similar in structure to the sheath of Henle surrounding the nerves supplying the spindle. The capsule consists of several closely applied concentric cytoplasmic sheets. Each sheet is about 1,000 A thick and has no fenestrations. Many caveolae and vesicles in the cytoplasm suggest active transport through the sheets. The periaxial space fluid contains much solid material. It is suggested that the capsule and periaxial space regulate internal chemical environment. The interfibrillar structures are less evident in the polar regions of intrafusal fibres than in extrafusal fibres. Simple motor end-plates occur on the polar regions of intrafusal fibres. In the myotube region of the intrafusal fibre a peripheral zone of myofibrils surrounds a cytoplasmic core containing nuclei, mitochondria, Golgi bodies, reticulum, and a few lipid-like granules. Naked sensory endings lie on the myotube "in parallel" with the underlying myofilaments. Naked processes of the primary sensory ending deeply indent the muscle plasma membrane and the underlying wisps of myofilament in the nuclear bag region. The plasma membranes of sensory nerve ending and intrafusal muscle fibre are about 200 A apart.     

Neuromuscular organization of feline anterior sartorius: I. Asymmetric distribution of motor units.

The neuromuscular organization of feline anterior sartorius was examined using three experimental approaches. First, the branching pattern of the nerve supplying anterior sartorius was inspected in muscles taken from a large number of feline cadavers. All muscles were found to be supplied by two major nerve branches, one directed proximally and the other directed distally, and most muscles (42/51) had a third distinct branch that entered the muscle centrally. Second, the motoneuronal populations supplying the three nerve branches were investigated by electrophysiological techniques. Motoneurons that supplied axons to the distally-directed branch did not appear to have collaterals in more proximally-located branches. In contrast, other motoneurons supplying the proximally-directed branch also appeared to supply axon collaterals to the centrally-directed branch. This result suggested that the motoneuronal population of the distally-directed branch was largely separate from that supplying the proximally- and centrally-directed branches. Third, the motor unit territories supplied by different nerve branches were mapped using glycogen-depletion methods. Muscle fibers supplied by the distally-directed nerve branch were mostly distributed to the medial portion of anterior sartorius, whereas the fibers supplied by the other two branches were generally found more anteriorly. Further, the muscle fibers supplied by an individual nerve branch were present in greater numbers at the end of the muscle closest to the entry point of that branch. Thus, the motor units supplied by discrete nerve branches were found to be distributed asymmetrically within anterior sartorius, but were arranged neither strictly in-parallel nor strictly in-series.