Reflex Control of Abdominal Flexor Muscles in the Crayfish

1965 ◽  
Vol 43 (2) ◽  
pp. 229-246
Author(s):  
DONALD KENNEDY ◽  
KIMIHISA TAKEDA
Keyword(s):  
Neuromuscular Junctions ◽  
Reciprocal Relationship ◽  
Muscle Fibres ◽  
Reflex Inhibition ◽  
Motor Axons ◽  
Efferent Nerve ◽  
Temporal Properties ◽  
Presynaptic Mechanisms ◽  
Flexor Muscles ◽  
Central Inhibition

1. Fibres from the tonic, superficial abdominal flexor muscles in the crayfish receive a complex, highly polyneuronal innervation from among five motor axons and one inhibitor. All efferent nerve fibres show some degree of ‘spontaneous’ activity. 2. The muscle fibres therefore exhibit a constant flux of membrane potential, and hence of tension, in intact preparations. Depolarization is the result of facilitation and/or summation of junctional potentials of various amplitudes, and in some fibres of superimposed electrogenic responses. Neighbouring fibres tend to show similar innervation patterns, more distant ones dissimilar ones. 3. No useful distinction may be made between ‘fast’ and ‘slow’ motor axons. A given axon may produce junctional potentials of very different amplitudes (and some what different rise-times) in neighbouring muscle fibres while another exhibits a precisely reciprocal relationship. The largest axon produces facilitating junctional potentials in all the muscle fibres it innervates, but others may exhibit facilitation in one muscle fibre and antifacilitation in another. 4. Most muscle fibres are innervated by two or three excitatory axons; fibres with single, quadruple or quintuple motor innervation are relatively rare. There is a pronounced tendency for fibres with a rich excitatory innervation to receive the inhibitor as well. The innervation is not shared equally among motor axons: one serves over 90% of the muscle fibres, and two others 20% or less. Statistical analysis of the combinations of motor axons serving muscle fibres reveals that these are apparently random, with all variations from randomness accountable on the grounds of broad regional differences in distribution. 5. The motor axons are selectively activated by specific reflex inputs. Since muscle fibres receive, on the average, only a restricted sample of the available motor supply, it follows that they participate differentially in different reflex actions. Evidence is presented that the firing pattern of motor nerves is appropriate for the temporal properties of their neuromuscular junctions. 6. Reflex inhibition is accomplished by central inhibition of all excitatory motor outflow, accompanied by reciprocal firing in the inhibitor axon. This and the fact that less than half the muscle fibres receive inhibitory innervation demonstrate that, in contrast to the one other crustacean system analysed, reflex inhibition is primarily a central event. Peripheral inhibition in the slow flexor system must serve mainly as a device to achieve repolarization and thus terminate contractions. Such action necessarily depends upon post-synaptic rather than presynaptic mechanisms.

scholarly journals The effect of calcium and magnesium on the spontaneous release of transmitter at insect motor nerve terminals

1978 ◽  
Vol 75 (1) ◽  
pp. 101-112
Author(s):  
H. M. Washio ◽  
S. T. Inouye
Keyword(s):  
Calcium Concentration ◽  
Neuromuscular Junctions ◽  
Calcium Ionophore ◽  
Reciprocal Relationship ◽  
Magnesium Concentration ◽  
Extracellular Potassium ◽  
Muscle Fibres ◽  
Bathing Solution ◽  
Spontaneous Release ◽  
Calcium And Magnesium

1. The effect of the extracellular calcium and magnesium concentrations and calcium ionophore, X-537A, on the frequency of miniature excitatory post-synaptic potentials (MEPSPs) was studied in cockroach leg muscle fibres. 2. The frequency of MEPSPs increased as the calcium concentration was increased from 0.1 to 10 mM. In the presence of 10 mM magnesium, however, raising the calcium concentration from 0.1 to 1 mM slightly depressed the frequency. In saline containing elevated potassium (20.8 mM), increasing the calcium concentration produced a much higher frequency than that in the normal potassium saline (10.8 mM) in the absence of magnesium. Raising the extracellular potassium concentration was without effect unless the bathing solution contained calcium. 3. The frequency of the miniature potentials was reduced as the magnesium concentration was raised from 0 to 10 mM, depending on the presence of calcium ions. On the contrary, a slightly increased frequency was observed in the low calcium saline as the magnesium concentration was raised from 1 to 10 mM. The reciprocal relationship between calcium and magnesium and the time course of the effect suggest that both ions act at the same surface sites in the presynaptic membrane. 4. X-537A elicited a transient increase in frequency followed by a fall of the frequency to a very low rate. Further application of the ionophore was without effect. The effect of X-537A on the spontaneous release of transmitter at the insect neuromuscular junction was comparable with that on the spontaneous acetylcholine release in vertebrate neuromuscular junctions.

Reflex Control of Abdominal Flexor Muscles in the Crayfish

1965 ◽  
Vol 43 (2) ◽  
pp. 211-227 ◽  
Author(s):  
DONALD KENNEDY ◽  
KIMIHISA TAKEDA
Keyword(s):  
Giant Axon ◽  
Muscle Fibres ◽  
Motor Axons ◽  
Giant Fibre ◽  
Optimal Interval ◽  
Flexor Muscles ◽  
Muscle Types ◽  
Giant Fibres ◽  
Large Motor ◽  
Almost All

1. The flexor musculature of the crayfish abdomen is divided into two systems: a set of tonic superficial muscles, and a complex series of massive flexor muscles that produce powerful twitches but never exhibit tonic contractions. The muscle types are histologically differentiated, and also separately innervated: the main flexors receive ten large motor axons, and the slow superficial muscles six smaller ones. 2. Fibres of the main flexor muscles studied are almost all triply innervated; each receives endings from (a) the ‘motor giant’ axon, (b) one of several specific non-giant motor axons, and (c) a common inhibitor. 3. Excitatory junctional potentials (e.j.p.s) due to motor giant and non-giant axons are similar and large; each may trigger secondary, active ‘spikes’, thus often producing post-junctional responses of 100 mV. or more. The responses differ in that the motor giant e.j.p. shows a dramatic decrease upon repetitive stimulation, whereas that due to non-giant motor axons exhibits some facilitation. 4. Activity in the central giant fibres drives both motor axons. The response to both, when the motor giant system is fully rested, is slightly larger than that to either alone; when activated by stimulation of the central giant fibre the junctional potentials are evoked asynchronously due to differences in central reflex time, and double spiking in the muscle fibres sometimes results. Upon repeated stimulation the response to the giant is reduced to a very low level; this is accompanied by a decrease in the tension developed in successive reflexly evoked twitches. The motor giant system thus apparently functions to provide additional tension for the first few ‘flips’ in a series of swimming movements during escape. 5. Impulses in the inhibitor axon, even at the optimal interval, reduce the amplitude of excitatory post-junctional potentials by only a small amount; their effect in shortening duration is more notable. It is postulated that the peripheral inhibitor functions to cut short excitatory depolarizations and hence to terminate lingering tension that might oppose subsequent reflex actions.

scholarly journals Post-synaptic morphology of mouse neuromuscular junctions is linked to muscle fibre type

2020 ◽  
Author(s):  
Aleksandra M. Mech ◽  
Anna-Leigh Brown ◽  
Giampietro Schiavo ◽  
James N. Sleigh
Keyword(s):  
Motor Neuron ◽  
Muscle Fibre ◽  
Fibre Type ◽  
Neuromuscular Junctions ◽  
Fibre Diameter ◽  
Neuromuscular Diseases ◽  
Neuronal Morphology ◽  
Muscle Fibre Type ◽  
Muscle Membrane ◽  
Muscle Fibres

AbstractThe neuromuscular junction (NMJ) is the highly specialised peripheral synapse formed between lower motor neuron terminals and muscle fibres. Post-synaptic acetylcholine receptors (AChRs), which are found in high density in the muscle membrane, bind to acetylcholine released into the synaptic cleft of the NMJ, ultimately facilitating the conversion of motor action potentials to muscle contractions. NMJs have been studied for many years as a general model for synapse formation, development and function, and are known to be early sites of pathological changes in many neuromuscular diseases. However, information is limited on the diversity of NMJs in different muscles, whether muscle fibre type impacts NMJ morphology and growth, and the relevance of these parameters to neuropathology. Here, this crucial gap was addressed using a robust and standardised semi-automated workflow called NMJ-morph to quantify features of pre- and post-synaptic NMJ architecture in an unbiased manner. Five wholemount muscles from wild-type mice were dissected and compared at immature (post-natal day, P7) and early adult (P31-32) timepoints. Post-synaptic AChR morphology was found to be more variable between muscles than that of the motor neuron terminal and there were greater differences in the developing NMJ than at the mature synapse. Post-synaptic architecture, but not neuronal morphology or post-natal synapse growth, correlates with fibre type and is largely independent of muscle fibre diameter. Counter to previous observations, this study indicates that smaller NMJs tend to innervate muscles with higher proportions of fast twitch fibres and that NMJ growth rate is not conserved across all muscles. Furthermore, healthy pre- and post-synaptic NMJ morphological parameters were collected for five anatomically and functionally distinct mouse muscles, generating reference data that will be useful for the future assessment of neuromuscular disease models.Graphical Abstract

scholarly journals Myomirnas Role in Als Suggest a Crosstalk between Muscle and Motor Neuron

2018 ◽  
Author(s):  
Valentina Pegoraro ◽  
Antonio Merico ◽  
Corrado Angelini
Keyword(s):  
Skeletal Muscle ◽  
Motor Neuron ◽  
Aerobic Exercise ◽  
Muscle Atrophy ◽  
Motor Neurons ◽  
Neuromuscular Junctions ◽  
Neurodegenerative Disorder ◽  
Disease Process ◽  
Muscle Fibres ◽  
Wide Range

Amyotrophic lateral sclerosis (ALS) is a rare, progressive, neurodegenerative disorder caused by degeneration of upper and lower motor neurons. The disease process leads from lower motor neuron involvement to progressive muscle atrophy, weakness, fasciculations for the upper motor neuron involvement to spasticity. Muscle atrophy in ALS is caused by a dysregulation in the molecular network controlling fast and slow muscle fibres. Denervation and reinnervation processes in skeletal muscle occur in the course of ALS and are modulated by rehabilitation. MicroRNAs (miRNAs) are small non-coding RNAs that modulate a wide range of biological functions under various pathophysiological conditions. MiRNAs can be secreted by various cell types and they are markedly stable in body fluids. MiR-1, miR-133 a, miR-133b, and miR-206 are called “myomiRs” and are considered markers of myogenesis during muscle regeneration and neuromuscular junction stabilization or sprouting. We observed a positive effect of a standard aerobic exercise rehabilitative protocol conducted for six weeks in 18 ALS patients during hospitalization in our center. We correlated clinical scales with molecular data on myomiRs. After six weeks of moderate aerobic exercise, myomiRNAs were down-regulated, suggesting an active proliferation of satellite cells in muscle and increased neuromuscular junctions. Our data suggest that circulating miRNAs modulate during skeletal muscle recovery in response to physical rehabilitation in ALS.

Non-motile sensory cilia and neuromuscular junctions in a ctenophore independent effector organ

1965 ◽  
Vol 162 (988) ◽  
pp. 333-350 ◽  
Keyword(s):  
Neuromuscular Junctions ◽  
Ciliated Cell ◽  
Sensory Nerve ◽  
Spatial Summation ◽  
Muscle Cells ◽  
Sensory Cells ◽  
Muscle Fibres ◽  
Water Displacement ◽  
Single Finger ◽  
Effector Organ

Non-motile cilia of the (9 + 2) pattern, having a specialized onion-like root structure, act as sensitive receptors of water displacement and thereby detect vibrations of small objects in the water nearby. These receptors are situated on sensory nerve cells on finger-like processes up to 1 cm long, on the surface of the ctenophore Leucothea ( = Eucharis) multicornis . In response to vibration a single finger can shoot outwards as an independent effector by an extension of its mesogloeal hydrostatic skeleton, acted on by circular and transverse muscle fibres which run mainly through the mesogloea. A copepod which may be hit is immobilized, presumably by a poisonous secretion. Retraction is brought about by longitudinal ectodermal fibres. The neuromuscular junctions have presynaptic vesicles of 30 to 50 nm diameter, a cleft of 15 to 20 nm wide, and occur at discrete points far from each other on the muscle cells, suggesting that excitation is propagated along the muscle fibres. No direct connexion has been traced between a sensory ciliated cell and a muscle fibre, but sensory cells connect with nerve net neurons and these form synapses with each other and with muscle cells. There are numerous nerve fibres in the epithelium and synapses with vesicles on one side of a cleft 12 to 15 nm wide occur between them sufficiently closely for spatial summation to be possible. The separate co-ordination of movements of extension, retraction and bending requires that certain types of sensory cells be connected specifically, if in directly, with muscle fibres of a particular directionality. This provides a primitive example of specificity of connexions which must imply two overlapping nerve nets.

The Activity of Single Motor Fibres in Arthropods I. The Dragonfly Nymph

1965 ◽  
Vol 42 (3) ◽  
pp. 447-461
Author(s):  
ANN KNIGHTS
Keyword(s):  
Electrical Stimulation ◽  
Temporal Summation ◽  
Reciprocal Relationship ◽  
Response Patterns ◽  
Insect Muscle ◽  
Frequency Sensitivity ◽  
Single Motor ◽  
Dragonfly Nymph ◽  
Central Inhibition ◽  
Stimulation Of

1. Responses to mechanical and electrical stimulation have been investigated in single motor fibres dissected in the segmental nerves of the dragonfly nymph. 2. A large proportion of fibres possessed a background discharge which was often accelerated of inhibited on stimulation. Examples of central inhibition were common. 3. Efferent responses varied in type, delay and regularity, both with the input under stimulation and with the frequency and intensity of the volley. The majority of fibres responded to stimulation of more than one nerve root. 4. In many motor fibres changes in the parameters of stimulation demonstrated a reciprocal relationship between and frequency. An enhanced responsiveness occurred with frequency increases in the range of 10-100/sec. indicatind a considerable importance of temporal summation/facilitation. 5. The characteristic frequency-sensitivity of motor fibres and the variability of their response patterns are discussed in relation to the control of insect muscle.

Modulatory effects of nitric oxide on synaptic depression in the crayfish neuromuscular system

2000 ◽  
Vol 203 (23) ◽  
pp. 3595-3602 ◽  
Author(s):  
H. Aonuma ◽  
T. Nagayama ◽  
M. Takahata
Keyword(s):  
Nitric Oxide ◽  
Neuromuscular Transmission ◽  
Procambarus Clarkii ◽  
Synaptic Depression ◽  
Physiological Property ◽  
Muscle Fibres ◽  
Flexor Muscle ◽  
Bath Application ◽  
Flexor Muscles ◽  
Stimulation Of

A characteristic physiological property of the neuromuscular junction between giant motor neurones (MoGs) and fast flexor muscles in crayfish is synaptic depression, in which repetitive electrical stimulation of the MoG results in a progressive decrease in excitatory junction potential (EJP) amplitude in flexor muscle fibres. Previous studies have demonstrated that l-arginine (l-Arg) modulates neuromuscular transmission. Since l-Arg is a precursor of nitric oxide (NO), we examined the possibility that NO may be involved in modulating neuromuscular transmission from MoGs to abdominal fast flexor muscles. The effect of a NO-generating compound, NOC7, was similar to that of l-Arg, reversibly decreasing the EJP amplitude mediated by the MoG. While NOC7 reduced the amplitude of the EJP, it induced no significant change in synaptic depression. In contrast, a scavenger of free radical NO, carboxy-PTIO, and an inhibitor of nitric oxide synthase, l-NAME, reversibly increased the EJP amplitude mediated by MoGs. Synaptic depression mediated by repetitive stimulation of MoGs at 1 Hz was partially blocked by bath application of l-NAME. Bath application of a NO scavenger, a NOS inhibitor and NO-generating compounds had no significant effects on the depolarisation of the muscle fibres evoked by local application of l-glutamate. The opposing effects on EJP amplitude of NOC7 and of carboxy-PTIO and l-NAME suggest that endogenous NO presynaptically modulates neuromuscular transmission and that it could play a prominent role at nerve terminals in eliciting MoG-mediated synaptic depression in the crayfish Procambarus clarkii.

Ultrastructure of intraocular muscles of diving and nondiving ducks

1982 ◽  
Vol 60 (7) ◽  
pp. 1588-1606 ◽  
Author(s):  
J. G. Sivak ◽  
O. E. Vrablic
Keyword(s):  
Neuromuscular Junctions ◽  
Muscle Fibres ◽  
Dark Cell ◽  
Domestic Ducks ◽  
Diving Ducks ◽  
Light Cell ◽  
Axon Terminals ◽  
End Plate ◽  
Transmission Electron ◽  
Skeletal Muscle Fibres

The fine structure of ciliary muscle (CM), iris sphincter (IS), and neuromuscular junctions (NMJ) were studied by light and transmission electron microscopy in domestic ducks (Anas platyrhynchos) and diving ducks (Mergus merganser). Previous work has shown that the iris produces exaggerated acommodative ability in the diver. Both muscles are striated in the two species. While both muscles of domestic ducks and the CM of the diving ducks consist of one cell type, the IS of the latter is made up of two types of cells referred to as "light" and "dark." The "light" cell has long, thin, uniformly distributed mitochondria, while in the "dark" cells they are large, unevenly dispersed and often aggregated subsarcolemmally. The sarcoplasmic reticulum is more abundant in both IS and CM of domestic ducks, while well developed T tubules are seen more regularly in the intraocular muscles of diving ducks.The NMJ's do not show the complexity seen in singly innervated skeletal muscle fibres. All the nerve axon terminals end in a flat shallow trough and postjunctional folds are either nonexistent or very shallow. The NMJ's of the IS of domestic ducks and of the "dark" cell of the IS of diving ducks consist of a large single end plate. That of the CM of domestic ducks consists of a diffuse single end plate while the NMJ of the CM of diving ducks consists of diffuse multiple endings. Nerve endings of similar size and structure but occurring only singly were found on the "light" cell of the IS of domestic ducks.

The innervation of the ampulla of the tube foot in the starfish Astropecten irregularis

1967 ◽  
Vol 168 (1010) ◽  
pp. 91-99 ◽  
Keyword(s):  
Methylene Blue ◽  
Electron Microscope ◽  
Neuromuscular Junctions ◽  
Muscle Cells ◽  
Central Core ◽  
Muscle Fibres ◽  
Nerve Fibres ◽  
Clear Cytoplasm ◽  
Tube Feet

In the ampullae of the starfish Astropecten irregularis extensions stretch from the main soma of the muscle cells down the seams of the ampullae into bulbs of tissue in the tube feet. Their terminations range from 0.2 to 4.0 μm in diameter. Here axons in tracts from the radial cord form synapses upon the extensions of the muscle cells. In sections examined with the electron microscope the extensions are distinguished from nerves by their central core of myofilaments, surrounded by clear cytoplasm. The junctions between the extensions of the muscle cells and the nerve fibres show no peculiarities of the membrane and are recognized as synapses only by their vesicles. No nerve fibres or neuromuscular junctions can be identified in the ampulla, and structures described from material vitally stained with methylene blue must be reinterpreted. The fibres which run along the seam of the ampullae, formerly described as axons, are extensions of muscle cells, to which they can be traced. The muscle fibres of the ampullae have large fluid-filled spaces around the myofilaments and it is proposed that some stain selectively and give rise to the structures originally described as ribbon axons.

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