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

1982 ◽  
Vol 216 (1202) ◽  
pp. 103-110 ◽  
Keyword(s):  
Electron Microscopy ◽  
Motor Nerve ◽  
Sensory Nerve ◽  
Muscle Spindles ◽  
Sublethal Dose ◽  
Muscle Fibres ◽  
Nerve Terminals ◽  
Intrafusal Muscle ◽  
Almost All ◽  
Latrodectus Mactans

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.

The structure and innervation of the nuclear bag muscle fibre system and the nuclear chain muscle fibre system in mammalian muscle spindles

1962 ◽  
Vol 245 (720) ◽  
pp. 81-136 ◽  
Keyword(s):  
Muscle Fibre ◽  
Motor Nerve ◽  
Sensory Nerve ◽  
Muscle Spindles ◽  
Equatorial Region ◽  
Muscle Fibres ◽  
Nerve Fibres ◽  
Intrafusal Fibres ◽  
Nuclear Chain ◽  
Nuclear Bag

1. The structure and innervation of muscle spindles from normal, de-afferented and de-efferented muscles of the cat hind limb were studied. The spindles were either completely isolated by microdissection, or were serially sectioned transversely. 2. All spindles contain two distinct types of intrafusal muscle fibre, ‘nuclear bag fibres’ and ‘nuclear chain fibres’, which differ in structure and innervation. 3. Nuclear bag muscle fibres, usually two per spindle, are less than half the diameter of extrafusal fibres, and each contains numerous large nuclei packed together in the equatorial region of the spindle. Nuclear bag fibres practically never branch. The fibres contain numerous myofibrils uniformly distributed in cross-sections, and relatively little sarcoplasm; they atrophy very slowly after the ventral spinal roots are cut. Several small motor nerve fibres (y, fibres) enter each spindle and terminate in a number of discrete motor end-plates on the nuclear bag muscle fibres. These y x end-plates lie in a group at each spindle pole and long lengths of nuclear bag fibre are free of motor innervation. 4. Nuclear chain muscle fibres, usually four per spindle, are about half the length and diameter of nuclear bag fibres in spindles in the leg muscles. The nuclear chain fibres in spindles from the small muscles of the foot may, however, equal the nuclear bag fibres in length, and in diameter beyond the ends of the lymph space. Each nuclear chain fibre contains a single row of central nuclei in the equatorial region; the fibres occasionally branch, but often none of them do so. They contain fewer myofibrils per unit area, irregular in size and distribution, and relatively more sarcoplasm, than nuclear bag fibres. Nuclear chain fibres atrophy nearly as rapidly as extrafusal fibres after the ventral roots are cut. A number of very fine motor nerve fibres fibres) enter each spindle and terminate in a network of fine axons and small nerve endings (the network’) situated on the nuclear chain muscle fibres in most regions other than the nuclear region. 5. All spindles receive both y 1 xand y 2 innervation, fibres forming slightly more than half of the total number of motor fibres which varies from seven in simple spindles in phasic muscles to twenty-five in the most complex spindles in tonic muscles. Both y 1 and y 2 fibres remain intact after dorsal root transection and degenerate following ventral root transection. The histological evidence supports the view that the yj and y2 nerve fibres at the spindles are derived from two types of stem fibre, neither of which belongs to the a group. 6. Each spindle has one primary sensory nerve ending, supplied by one group 1 a afferent nerve fibre, and from zero to five secondary sensory nerve endings, each supplied by one group II afferent nerve fibre. The primary sensory terminations lie on both nuclear bag and nuclear chain muscle fibres. The secondary sensory terminations lie predominantly on the nuclear chain muscle fibres. In spindles with several secondary sensory endings, their terminations may lie on the same region of nuclear chain fibres as motor endings of the y 2 network. 7. In general, spindles in tonic muscles have more secondary sensory endings and motor nerve fibres and endings than those in other muscles. Nuclear chain intrafusal fibres are probably functionally ‘slower’ than nuclear bag intrafusal fibres, while both types are ‘slower’ than extrafusal fibres. Both nuclear chain fibres and nuclear bag fibres, however, probably show a gradation in activity related to the nature of the muscle in which they lie. The reader is advised to study figure 33 and its legend first, at the same time studying the plate figures to which reference is made in figure 33 b , then to read the portions of the Results in italics consecutively followed by the Discussion, finally studying the detailed Results. Further details of many of the illustrations and tables are available for reference in the Archives of the Royal Society.

Visual identification of nerve terminals in living isolated skeletal muscle

1972 ◽  
Vol 181 (1065) ◽  
pp. 421-430 ◽  
Keyword(s):  
Electron Microscopy ◽  
Schwann Cells ◽  
Motor Nerve ◽  
Postsynaptic Membrane ◽  
Muscle Fibres ◽  
Nerve Terminals ◽  
Necturus Maculosus ◽  
Visual Identification ◽  
Collagenase Treatment ◽  
Nerve Muscle

1. The unmyelinated terminal branches of motor nerve fibres were clearly resolved in live, unstained skeletal muscles of the frog and of the mudpuppy (Necturus maculosus), using Nomarski optics. The observations were supplemented by several histological procedures, including electron microscopy, and by extracellular recordings from the nerve terminals. 2. In live motor nerve terminals of the mudpuppy one can see a series of varicosities, which in the electron microscope are shown to contain accumulations of synaptic vesicles. Junctional folds in the muscle fibres are confined to the areas opposite the varicosities. Terminal branches of the frog’s motor axon are also varicose, but the swellings are so closely spaced that they can be seen only after staining or by electron microscopy. 3. Nuclei of Schwann cells are recognized along living nerve terminals. Electrophoretic injection of a fluorescent dye, Procionyellow, into the cell bodies of Schwann cells enables one to see the distribution of their processes with the light microscope. 4. Visibility of terminal arborizations was improved by bathing nerve-muscle preparations in solutions of collagenase for 15 to 30 min, thereby removing much of the connective tissue. After longer collagenase treatment nerve terminals could be lifted off muscle fibres with a micropipette, thus exposing the postsynaptic membrane.

scholarly journals Acetylcholinesterase from the motor nerve terminal accumulates on the synaptic basal lamina of the myofiber.

1991 ◽  
Vol 115 (3) ◽  
pp. 755-764 ◽  
Author(s):  
L Anglister
Keyword(s):  
Basal Lamina ◽  
Ache Activity ◽  
Neuromuscular Junctions ◽  
Motor Nerve ◽  
Synaptic Cleft ◽  
Motor Nerve Terminal ◽  
Nerve Terminals ◽  
Axon Terminals ◽  
Muscle Nerve ◽  
Almost All

Acetylcholinesterase (AChE) in skeletal muscle is concentrated at neuromuscular junctions, where it is found in the synaptic cleft between muscle and nerve, associated with the synaptic portion of the myofiber basal lamina. This raises the question of whether the synaptic enzyme is produced by muscle, nerve, or both. Studies on denervated and regenerating muscles have shown that myofibers can produce synaptic AChE, and that the motor nerve may play an indirect role, inducing myofibers to produce synaptic AChE. The aim of this study was to determine whether some of the AChE which is known to be made and transported by the motor nerve contributes directly to AChE in the synaptic cleft. Frog muscles were surgically damaged in a way that caused degeneration and permanent removal of all myofibers from their basal lamina sheaths. Concomitantly, AChE activity was irreversibly blocked. Motor axons remained intact, and their terminals persisted at almost all the synaptic sites on the basal lamina in the absence of myofibers. 1 mo after the operation, the innervated sheaths were stained for AChE activity. Despite the absence of myofibers, new AChE appeared in an arborized pattern, characteristic of neuromuscular junctions, and its reaction product was concentrated adjacent to the nerve terminals, obscuring synaptic basal lamina. AChE activity did not appear in the absence of nerve terminals. We concluded therefore, that the newly formed AChE at the synaptic sites had been produced by the persisting axon terminals, indicating that the motor nerve is capable of producing some of the synaptic AChE at neuromuscular junctions. The newly formed AChE remained adherent to basal lamina sheaths after degeneration of the terminals, and was solubilized by collagenase, indicating that the AChE provided by nerve had become incorporated into the basal lamina as at normal neuromuscular junctions.

The Innervation of the Muscle-Spindle

1948 ◽  
Vol s3-89 (6) ◽  
pp. 143-185
Author(s):  
D. BARKER
Keyword(s):  
Muscle Spindles ◽  
Muscle Fibres ◽  
Gold Chloride ◽  
Nerve Fibres ◽  
Intrafusal Muscle ◽  
Intrafusal Fibre ◽  
Afferent Discharge ◽  
Tendon Organ ◽  
Nuclear Bag ◽  
Secondary Fibre

A study of the morphology and innervation of muscle-spindles from the quadriceps of the rabbit and cat has shown that: 1. The intrafusal muscle-fibres do not subdivide in their course through the spindle, as is maintained in some descriptions, but retain their individuality from pole to pole. 2. There is no constant feature which is characteristic of one pole of a spindle and not the other. A distinction can be made between the proximal and distal ends only when it is possible to orientate the spindle according to the proximal and distal ends of the muscle. The extreme ends of the spindle are attached indifferently to extrafusal endomysium, tendon, or perimysial connective tissue. 3. In the equatorial region each muscle-fibre of the spindle contains a dense aggregation of spherical central nuclei (‘nuclear bag’). On either side of this aggregation oval nuclei are disposed in the form of a chain within a central core of protoplasm (‘myotube region’). The nuclear bag is devoid of cross-striations and presumably non-contractile. The two polar portions of the muscle-fibre on either side of the bag are striated and each receives a motor innervation; hence they are presumed to function as independent contractile units. 4. The number of end-plates possessed by a spindle is approximately double its number of intrafusal muscle-fibres, with half the total number of end-plates situated at each pole. The ratio is rarely exact, since one polar half of an intrafusal fibre frequently bears two end-plates; these are innervated by nerve-fibres which retain their individuality as far as they can be traced back from the spindle. Both small nerve-fibres (3-4 µ in gold chloride preparations) and relatively large nerve-fibres (6-7 µ in gold chloride preparations) take part in the motor innervation of muscle-spindles, as was deduced on physiological grounds by Leksell (1945). 5. An analysis of the sensory innervation has confirmed many of Ruffini's (1898) observations. Primary or ‘annulo-spiral’ and secondary or ‘flowerspray’ endings occur and they are innervated by independent nerve-fibres; it is suggested that Ruffini's terms ‘primary’ and ‘secondary’ be adopted since the descriptive terms cannot always be applied. In the rabbit the secondary ending is ‘annulo-spiral’ in form and differs little from the primary ending; in the cat it is more irregular and could be termed ‘flower-spray’. The primary ending is always present and is associated with the nuclear bags of the intrafusal muscle-fibres; in some instances its ramifications are more extensive and also entwine the myotube regions. The primary ending may be the only sensory termination present, or it may be accompanied by one or by two secondary endings. These are borne by the myotube regions of the musclefibres. In the rabbit's quadriceps and interossei, spindles with one primary and one secondary ending were the most frequent in the samples taken; in the cat's quadriceps spindles with one primary and two secondary endings were the most numerous. Both the primary and secondary nerve-fibres invariably ramify so as to innervate each intrafusal fibre in the muscle-bundle. The two sensory terminations are often closely intercalated but do not overlap with one another to any great extent. As estimated from measurements made on fresh, silver, and gold chloride preparations the total diameter of the primary fibre lies between 8 and 12 µ, that of the secondary fibre between 6 and 9 µ. 6. Apart from small sympathetic fibres innervating the vascular supply of the spindle, other finer fibres may occasionally be seen ramifying within the walls of the capsule and over the polar regions. It is possible that they are somatic sensory fibres subserving the sensation of pain. 7. The nature of the reflex effects of the afferent impulses discharged by the muscle-spindle and tendon-organ is considered, and it is concluded that the balance of evidence indicates that the afferent discharge from the spindle is excitatory and that from the tendon-organ inhibitory to the motor neurones of the same muscle. However, the identification of the spindle as the receptor which excites the stretch reflex is found to rest largely upon equivocal evidence, its acceptance depending ultimately upon Matthews's finding (1933) of a considerable difference-in threshold between the spindle and tendon-organ in response to stretch. It is suggested that the large primary fibre innervating the spindle should be identified as the ‘stretch afferent’ rather than the smaller secondary fibre specified by Matthews, for the rapid con duction rate of the afferent discharge exciting the stretch reflex (Lloyd, 1943) indicates that sensory fibres of the largest diameter are employed. The functional significance of the secondary fibres is obscure and the specific reflex functions of the sensory fibres innervating both the spindle and the tendon organ clearly require further elucidation.

The Early Development of Muscle Spindles in the Rat

1973 ◽  
Vol 12 (1) ◽  
pp. 175-195
Author(s):  
ALICE MILBURN
Keyword(s):  
Close Association ◽  
Large Diameter ◽  
Muscle Spindles ◽  
Muscle Fibres ◽  
Intrafusal Muscle ◽  
Intrafusal Fibres ◽  
Fusimotor Innervation ◽  
Nuclear Chain ◽  
Intramuscular Nerve

The morphogenesis of muscle spindles in rat lower hind-limb muscles has been investigated using the electron microscope. The earliest detectable spindles are seen in the 19.5-day foetus and consist of a single myotube bearing simple nerve terminals of the large primary afferent axon from nearby unmyelinated intramuscular nerve trunks. The capsule forms by an extension of the perineural epithelium of the supplying nerve fasciculus, and is confined initially to the innervated zone. Myonuclei accumulate in this region, so that the first intrafusal muscle fibre to develop is a nuclear-bag fibre. Myoblasts, present within the capsule of the spindle throughout its development, fuse to form a smaller less-differentiated myotube by the 20-day foetal stage. This new myotube matures by close association with the initial fibre, and by birth (21-22 days gestation) has formed the smaller, intermediate bag fibre, that has been identified histochemically and ultrastructurally in the adult. The nuclear-chain fibres develop in the same way; myoblasts fuse to form satellite myotubes that mature in pseudopodial apposition to one of the other fibres within its basement membrane. This apposition consists of extensions of sarcoplasm from the developing myotube into the supporting fibre. By the 4-day postnatal stage the full adult complement of 4 intrafusal muscle fibres is present, although ultrastructural variations, seen in the adult, are not differentiated. The fusimotor innervation begins to arrive at birth, but is not mature until the 12th postnatal day, when the myofibrillar ultrastructural differentiation, including the loss of the M-line in the large-diameter bag fibre, is complete. The periaxial space appears at the same time. It is suggested that the sequential development of the intrafusal fibres is a reflexion of the decreasing morphogenetic effect of the afferent innervation, whereas the role of the fusimotor innervation is in ultrastructural, myofibrillar differentiation.

Form and classification of motor endings in mammalian muscle spindles

1985 ◽  
Vol 225 (1239) ◽  
pp. 195-212 ◽  
Keyword(s):  
Muscle Fibre ◽  
Fibre Type ◽  
Muscle Spindles ◽  
Muscle Fibre Type ◽  
Motor Axon ◽  
Muscle Fibres ◽  
Intrafusal Muscle ◽  
Axon Terminals ◽  
Hindlimb Muscle

The presynaptic features of 234 motor endings supplied to cat hindlimb muscle spindles have been studied in teased, silver preparations, and the postsynaptic features of a further 27 endings have been studied in serial, 1 μm thick, transverse sections. In the presynaptic study motor endings received by the three types of intrafusal muscle fibre were compared with the endings supplied to spindles by the various functional categories of motor axon. Three forms of motor ending were found that had significantly different presynaptic features. These forms correspond closely to those previously identified in the literature as p 1 (β), p 2 (dynamic γ) and trail (static γ). The results of the postsynaptic study showed that the degree of indentation of the intrafusal muscle fibres by motor axon terminals increases with greater distance from the primary ending, irrespective of muscle-fibre type. We conclude that the postsynaptic form of intrafusal motor endings is determined by distance from primary ending and muscle-fibre type. It is not determined by type of motor axon, and cannot be correlated with presynaptic form so as to produce a unified classification of intrafusal motor endings.

Propagation of electric activity in motor nerve terminals

1965 ◽  
Vol 161 (985) ◽  
pp. 453-482 ◽  
Keyword(s):  
Motor Nerve ◽  
Electric Activity ◽  
Muscle Fibres ◽  
Nerve Terminals ◽  
Terminal Branch ◽  
Direct Stimulation ◽  
Motor Nerve Terminals ◽  
End Plate ◽  
Synaptic Terminals ◽  
Set Up

External micro-electrodes were used to stimulate non-myelinated motor nerve terminals and to record pre- and post-synaptic responses at the neuromuscular junction of the frog. The synaptic terminals of the motor axon are electrically excitable. Antidromic nerve impulses can be set up by local stimulation of terminals along the greater part of their length. Presynaptic spikes can be recorded from the non-myelinated terminal parts of motor axons. As the impulse proceeds towards the tip of the terminal branch, the shape of the spike changes from a predominantly negative to a predominantly positive-going wave. Similar changes occur in muscle fibres near their tendon junctions, and can be attributed to the special local-circuit conditions at the ‘closed end’ of a fibre. The velocity of impulse propagation in motor nerve endings was determined by three different methods: ( a ) from the latency of antidromic nerve spikes elicited at different points along terminals, ( b ) from two-point recording of spikes along a terminal, ( c ) from the differential latency of focal end-plate potentials recorded at two spots of a myoneural junction. The average velocity obtained by these methods was approximately 0.3 m/s at 20 °C. Extracellular muscle fibre spikes recorded at junctional spots showed no significant differences from those recorded elsewhere, provided the spikes were initiated by direct stimulation and did not coincide with transmitter action. Direct current polarization produces a graded increase in frequency of miniature end-plate potentials when the endings are being depolarized, and sudden high-frequency bursts during excessive hyperpolarization. External two-point recording shows that these bursts arise independently at different spots of the synaptic terminals.

A dual effect of cobalt ions on the spontaneous release of transmitter at insect motor nerve terminals

1982 ◽  
Vol 98 (1) ◽  
pp. 353-361
Author(s):  
H. Washio
Keyword(s):  
External Surface ◽  
Motor Nerve ◽  
Reciprocal Relationship ◽  
Muscle Fibres ◽  
Nerve Terminals ◽  
Spontaneous Release ◽  
Dual Effect ◽  
Competitive Antagonist ◽  
Cobalt Ions ◽  
Equilibrium Dissociation

1. The effect of extracellular cobalt on the frequency of miniature excitatory post-synaptic potentials (MEPSPs) was studied in cockroach leg muscle fibres that had been depolarized with 20.8 mM-K saline. 2. Cobalt ions had a dual effect on the spontaneous release of transmitter, an inhibitory action being followed by an acceleratory. A reciprocal relationship between Ca2+ and Co2+ was found for both the inhibitory and acceleratory effects. 3. The equilibrium dissociation constant for Co2+ as a competitive antagonist of spontaneous release ranged from 0.4 to 0.65 mM. It is concluded that Co2+ is much more potent than Mg2+ in suppressing spontaneous transmitter release at the insect neuromuscular junction. The antagonism by extracellular Co2+ appears to occur only at the external surface site on the terminal membrane.

Sign in / Sign up

Export Citation Format

Share Document