Collateral Innervation of Muscle Fibres by Motor Axons of Dystrophic Motor Units

Nature ◽  
1973 ◽  
Vol 246 (5434) ◽  
pp. 500-501 ◽  
Author(s):  
JOHN E. DESMEDT ◽  
S. BORENSTEIN
Keyword(s):  
Motor Units ◽  
Muscle Fibres ◽  
Motor Axons

Motor Unit Distribution of the Dorsal Longitudinal Flight Muscles in Locusts

1963 ◽  
Vol 40 (1) ◽  
pp. 123-136
Author(s):  
A. C. NEVILLE
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Average Diameter ◽  
Fast Response ◽  
Muscle Fibres ◽  
Recurrent Nerve ◽  
Motor Axons ◽  
Flight Muscles ◽  
Large Motor ◽  
Longitudinal Muscles

1. The peripheral pathways of the ‘fast’ motor fibres to the locust dorsal longitudinal flight muscles are described at the single unit level, from electrophysiological and histological studies. This is summarized in a diagram on Pl. 1. 2. Both pterothoracic dorsal longitudinal muscles consist of five anatomically distinct motor units, arranged in layers from dorsal to ventral. Each of the four more ventral units of both muscles receives a motor axon from the segment in front via the recurrent nerve, whereas the uppermost motor unit is innervated in each case from the segment containing the muscle. The motor units are nearly equal both in size and capability for work. 3. Each of the five ‘fast’ motor axons innervates one topographically distinct bundle of muscle fibres. There is no overlap between muscle motor units. 4. Even within a single muscle, motor units are capable of vibrating at independent frequencies. This indicates that the coupling of units which occurs during flight is neither structurally nor functionally rigid. 5. With respect to peripheral features, the motor units within each dorsal longitudinal muscle are designed for fast response which improves the synchronization when the relevant neurons fire simultaneously (large motor axons, 15-25 µ in average diameter with high propagation velocity, 8 m./sec. at flight temperature). 6. It is suggested that a tonic motor output, containing at least three units, which was recorded from mesothoracic nerve IBa, travels to the small lateral dorsal muscles.

scholarly journals Neuromuscular Physiology of the Closer Muscles in the Pedipalp of the Scorpion Leiurus Quinquestriatus

1970 ◽  
Vol 52 (2) ◽  
pp. 325-344
Author(s):  
ARIEH GILAI ◽  
I. PARNAS
Keyword(s):  
Muscle Fibre ◽  
Motor Units ◽  
Input Resistance ◽  
Single Stimulus ◽  
Muscle Fibres ◽  
Motor Axons ◽  
Junction Potential ◽  
Peripheral Inhibition

1. The closing system of the pedipalp claw in the scorpion is composed of two agonistic muscles situated in both the patella (the longer closer muscle) and tibia (the short closer muscle). 2. Membrane electrical constants of the muscle fibres were found to be: λ = 0.6 mm.; ri = 1 x 106 Ωmm.-1; Ri = 280 Ωcm.; rm = 4.4 x 105 Ωmm.; Rm = 830 Ωcm.2; Cm. = 3.6 µF. cm.-2; τ = 3.0 msec.; input resistance = 3.3 x 105 Ω. 3. Each muscle fibre is multiterminally innervated by two motor axons, one initiating a junction potential and the second inducing a post-synaptic spike-like response. 4. The long closer muscle is composed of two anatomically distinct motor units, the short closer muscle of three motor units. Each unit is innervated by its own pair of specific motor axons. 5. No distinction between ‘slow’ and ‘fast’ axons or muscle fibres could be observed. Both muscles responded with a twitch to a single stimulus applied to the nerve. 6. No peripheral inhibition was observed.

scholarly journals Chromatophore Motor Units in Eledone Cirrhosa (Cephalopoda: Octopoda)

1985 ◽  
Vol 117 (1) ◽  
pp. 415-431 ◽  
Author(s):  
F. DUBAS ◽  
P.R. BOYLE
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Video Camera ◽  
Muscle Fibres ◽  
Motor Axons ◽  
Individual Muscle ◽  
Nerve Bundles ◽  
Suction Electrode ◽  
Electrical Impulses

Innervation of chromatophore muscles of the octopus Eledone cirrhosa was investigated by stimulating nerve bundles in the skin with a suction electrode and monitoring chromatophore movements with a photo-cell or a video camera. Attention was focused on the organization of the chromatophore muscle fibres into motor units. Individual muscle fibres respond to single electrical impulses with twitch-like contractions that do not facilitate with repetition, but summate to a smooth tetanus at about 10–15 Hz. At tetanic frequency, the degree of expansion of single chromatophores is always maximal. However, the number of expanded chromatophores can be graded by variations of either the stimulus voltage or frequency. Individual chromatophores and probably individual muscle fibres are part of several motor units. Chromatophores forming a given motor unit are found among chromatophores served by other motor axons. The motor units apparently form precise parts of natural patterning.

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.

Immunity to nerve growth factor and the effect on motor unit reinnervation in the rabbit

1992 ◽  
Vol 262 (5) ◽  
pp. R813-R818 ◽  
Author(s):  
D. I. Finkelstein ◽  
A. R. Luff ◽  
J. A. Schuijers
Keyword(s):  
Nerve Growth Factor ◽  
Growth Factor ◽  
Neural Crest ◽  
Conduction Velocity ◽  
Motor Units ◽  
Medial Gastrocnemius ◽  
Afferent Neuron ◽  
Motor Axons ◽  
Nerve Growth ◽  
Myelin Thickness

The trophic effects of nerve growth factor (NGF) on sympathetic, peripheral afferent, and other neural crest-derived cells have been intensively investigated. More recently, NGF has been shown to have an influence on motoneurons. This study was undertaken to investigate whether NGF had any influence on the mechanical or histological properties of reinnervated motor units. Three groups of rabbits were used: normal rabbits, rabbits in which the nerve to medial gastrocnemius (MG) was cut and allowed to reinnervate for 56 days, and rabbits in which the MG nerve reinnervated in the presence of immunity to NGF. Immunity to NGF did not affect the ability of motor axons to reinnervate a muscle, nor were the contractile characteristics of the motor units altered. The size of horseradish peroxidase-labeled motoneurons was not influenced by immunization against NGF; however, the distribution of afferent neuron sizes was altered. Conduction velocity of motor axons proximal to the neuroma was significantly faster after immunization against NGF. Transection and subsequent reinnervation by a peripheral nerve normally causes an increase in myelin thickness proximal to the neuroma. However, immunization against NGF appeared to decrease the magnitude of myelin thickening. It was concluded that immunization against NGF affects motor axonal conduction velocity via an influence on the neural crest-derived Schwann cells.

scholarly journals Neuromuscular organization of avian flight muscle: architecture of single muscle fibres in muscle units of the pectoralis (pars thoracicus) of pigeon (Columba livia)

1999 ◽  
Vol 354 (1385) ◽  
pp. 917-925 ◽  
Author(s):  
A. J. Sokoloff ◽  
G. E. Goslow
Keyword(s):  
Motor Unit ◽  
Cross Sections ◽  
Unit Length ◽  
Muscle Length ◽  
Motor Units ◽  
Columba Livia ◽  
Muscle Fibres ◽  
Cross Sectional ◽  
Total Length ◽  
Fast Twitch

The M. pectoralis (pars thoracicus) of pigeons ( Columba livia ) is comprised of short muscle fibres that do not extend from muscle origin to insertion but overlap ‘in-series’. Individual pectoralis motor units are limited in territory to a portion of muscle length and are comprised of either fast twitch, oxidative and glycolytic fibres (FOG) or fast twitch and glycolytic fibres (FG). FOG fibres make up 88 to 90% of the total muscle population and have a mean diameter one-half of that of the relatively large FG fibres. Here we report on the organization of individual fibres identified in six muscle units depleted of glycogen, three comprised of FOG fibres and three comprised of FG fibres. For each motor unit, fibre counts revealed unequal numbers of depleted fibres in different unit cross-sections. We traced individual fibres in one unit comprised of FOG fibres and a second comprised of FG fibres. Six fibres from a FOG unit (total length 15.45 mm) ranged from 10.11 to 11.82 mm in length and averaged (±s.d.) 10.74±0.79 mm. All originated bluntly (en mass) from a fascicle near the proximal end of the muscle unit and all terminated intramuscularly. Five of these ended in a taper and one ended bluntly. Fibres coursed on average for 70% of the muscle unit length. Six fibres from a FG unit (total length 34.76 mm) ranged from 8.97 to 18.38 mm in length and averaged 15.32 ±3.75 mm. All originated bluntly and terminated intramuscularly; one of these ended in a taper and five ended bluntly. Fibres coursed on average for 44% of the muscle unit length. Because fibres of individual muscle units do not extend the whole muscle unit territory, the effective cross-sectional area changes along the motor unit length. These non-uniformities in the distribution of fibres within a muscle unit emphasize that the functional interactions within and between motor units are complex.

The sensory and motor innervation of Nereis

1964 ◽  
Vol 159 (977) ◽  
pp. 652-667 ◽  
Keyword(s):  
Escape Response ◽  
Body Wall ◽  
Muscle Fibres ◽  
Motor Axons ◽  
Motor Innervation ◽  
Anatomical Basis ◽  
Stretch Receptors ◽  
Giant Fibres ◽  
Fast Twitch

The motor innervation of the segmental musculature of nereid polychaetes appears to be both polyneuronal and multiterminal, which closely resembles the condition found in the Arthropoda. The cell bodies of the motor axons lie in the cord and terminate in endings of the 'en grappe’ type on the surface of the muscle fibres. These observations provide an anatomical basis for the experiments that showed the muscles were capable of fast twitch-like contractions associated with the escape response and slower graded contractions normally seen during the ambulatory cycle of the parapodia. The sensory equipment of the parapodia includes several prominent neurons which function as rapidly adapting stretch receptors. Some of these are activated by the movements of the parapodia and body wall during locomotion and have inputs to the giant fibres and to an unpolarized network of sensory fibres within the cord. These receptors may serve to integrate the activity of individual segments and ensure co-ordinated flexibility of the movements of the worm as a whole.

The motor unit

2016 ◽  
Author(s):  
David Burke ◽  
James Howells
Keyword(s):  
Motor Unit ◽  
Neuromuscular Junctions ◽  
Discharge Rate ◽  
Motor Units ◽  
Motor Unit Action Potential ◽  
Muscle Fibres ◽  
Reflex Gain ◽  
Active Motor ◽  
Motor Unit Action ◽  
Fast Twitch

The motor unit represent the final output of the motor system. Each consists of a motoneuron, its axon, neuromuscular junctions, and muscle fibres innervated by that axon. The discharge of a motor unit can be followed by recording its electromyographic signature, the motor unit action potential. Motoneurons are not passive responders to the excitatory and inhibitory influences on them from descending and segmental sources. Their properties can change, e.g. due to descending monoaminergic pathways, which can alter their responses to other inputs (changing ‘reflex gain’). Contraction strength depends on the number of active motor units, their discharge rate, and whether the innervated muscle fibres are slow-twitch producing low force, but resistant to fatigue, fast-twitch producing more force, but susceptible to fatigue, or intermediate fast-twitch fatigue-resistant. These properties are imposed by the parent motoneurons, and the innervated muscle fibres have different histochemical profiles (oxidative, glycolytic, or oxidative-glycolytic, respectively).

Motoneuron and muscle-unit properties after long-term direct innervation of soleus muscle by medial gastrocnemius nerve in cat

1990 ◽  
Vol 64 (3) ◽  
pp. 847-861 ◽  
Author(s):  
R. C. Foehring ◽  
J. B. Munson
Keyword(s):  
Electrical Properties ◽  
Soleus Muscle ◽  
Previous Experiment ◽  
Muscle Fibers ◽  
Motor Units ◽  
Slow Muscle ◽  
Medial Gastrocnemius ◽  
Motor Axons ◽  
Lateral Gastrocnemius

1. This study addresses the following questions. 1) In a previous experiment, when the combined lateral gastrocnemius-soleus nerve was cross-innervated by the medial gastrocnemius (MG) nerve, was the predominance of slow muscle units in soleus muscle a result of selective routing of slow motor axons into soleus? 2) Is MG-nerve-induced conversion of soleus muscle fibers from slow to fast more complete at very long (18 mo vs. 9-11 mo) postoperative times? 3) Do MG motoneurons that cross-innervate soleus muscle recover their normal membrane electrical properties at very long postoperative times? 2. The proximal portion of approximately one-third of the MG nerve was coapted directly with the distally isolated soleus nerve. The MG muscle remained innervated by the unoperated portion of the MG nerve. At 6, 10, or 18 mos postoperative, motoneuron and/or muscle-unit properties were determined for MG motoneurons innervating MG, soleus, or neither muscle, and for axotomized soleus motoneurons. 3. In the partially denervated MG muscle, the proportions of motor units of each type were normal. This suggests that the population of MG motor axons that had been directed to the soleus nerve also contained a representative distribution of MG motoneuron types. 4. Most motor units (74%) in cross-innervated soleus (Xsoleus) were type S (based on muscle-unit contractile properties), in spite of the soleus nerve's having been cross-connected by approximately 75% fast MG motoneurons. Thus, even at very long postoperative times, slow soleus muscle units resisted conversion by fast MG motoneurons. 5. Thirty-two percent of MG motoneurons that had been cross-connected to soleus nerve elicited no measurable muscle contraction, compared with approximately 10% in previous reinnervation experiments in which the MG nerve was coapted with the MG or lateral gastrocnemius-soleus nerve. Thus MG motoneurons may be disadvantaged in their ability to innervate soleus muscle fibers. 6. It appears that at long postoperative times, those fast MG motoneurons tha had innervated large soleus muscle units had failed to convert those muscle fibers to fast types and had failed also to recover their normal motoneuron electrical properties. Conversion and recovery did occur for fast MG motoneurons that innervated small soleus muscle units and for slow MG motoneurons.

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