Cross-innervation of fast and slow-twitch muscles by motor axons of the sural nerve in the mouse

The extensor digitorum longus (EDL) or soleus muscles of adult mice were cross-innervated by the sural nerve (SN) and deprived of their original innervation. The number and sizes of motor units and the location of endplates in these muscles were studied 1.5 to 16 months later. In the EDL muscle, the SN cross-innervated the original endplates. Very few ectopic endplates were seen, even when the nerve was implanted well outside of the original endplate area. Only 3% of the fibres were polyneuronally innervated. In the soleus muscle, however, the SN formed large numbers of ectopic endplates whether the nerve was implanted in the original endplate zone or outside of it. In addition, 20% of the muscle fibres were polyneuronally innervated. The SN cross-innervated both EDL and soleus muscles completely. There was no preference for a particular group of the SN motoneurones since all the cross-innervated muscles were innervated by all SN motor axons and the motor unit sizes of the SN were similar in the cross-innervated EDL and soleus muscles. It is concluded that intrinsic properties of a muscle determine the ability to form ectopic synapses. The distribution of the motor unit sizes is determined by the particular pool of motoneurones which innervates the muscle.     

Observations on neuromuscular connection between the vagus nerve and skeletal muscle

The reinnervation of rat skeletal muscle fibres by the vagus nerve was studied. Vagal fibres in the rat can establish connections with regenerating muscle fibres and those muscle fibres supplied by the vagus become multiply innervated. The vagus nerve made connections with a normally innervated sternohyoid muscle when this muscle was rendered chemosensitive. Several endplates were formed by the vagus nerve on the same muscle fibre, and the structure of these differed from the endplates formed by the muscle's own nerve.If the muscle's own nerve and the vagus were cut and resutured into the sternohyoid muscle of the rat, many muscle fibres become innervated by their own nerve and by the vagus. Evidence is presented to show that each nerve established contacts at a separate site along the same muscle fibre. These connections were permanent, for even after 2 years following the operation the muscle was supplied by both nerves. Thus, in these experiments the muscle's own nerve did not ‘suppress’ the contacts made by an alien nerve. In rabbits the vagus and the accessory nerve were sutured into the sternomastoid muscle. Only a small proportion of the muscle became reinnervated by the vagus, whereas the accessory nerve reinnervated most of the muscle. Very few muscle fibres had become innervated by both nerves.The sternohyoid and sternomastoid are fast contracting muscles. When their fibres were reinnervated by the vagus nerve, their speed of contraction became significantly slower than those reinnervated by the original somatic motor nerve. The vagus nerve therefore determines the properties of the muscle fibres that it supplies. It is suggested that it is the slow tonic pattern of activity of the vagus nerves that determines the contractile speed of the muscles.     

Transformation of contraction speed in muscle following cross-reinnervation; dependence on muscle size

Summary The characteristics of isometric contractions and the force-velocity relation were studied in flexor digitorum longus, flexor hallucis longus and soleus muscles of the cat,in situ, at 37° C and with nerve stimulation. The two flexors were identified as typical fast twitch muscles and the soleus as a typical slow twitch muscle. Following self-reinnervation, both fast and slow muscles retained, to a large extent, their basic contraction characteristics. The soleus muscle, when cross-reinnervated with the nerve of either flexor hallucis longus muscle or extensor digitorum longus muscle exhibited a more complete slow-to-fast transformation than when cross-reinnervated with the nerve of flexor digitorum longus muscle. The flexor digitorum longus muscle underwent a greater degree of fast-to-slow transformation than the flexor hallucis longus muscle, when each was cross-reinnervated with the soleus nerve. The data previously reported for sarcomere shortening velocities of the cross-reinnervated muscles in the rat, the rabbit and the cat are reviewed in the light of present findings. It is found that the discrepancies obtained between species and between different muscles in the same species, with respect to the degree of muscle-speed transformation following cross-reinnervation, are correlated with the differences in the size-ratio of the muscles used in the cross-reinnervation procedure.     

Adaptive range of myosin heavy chain expression in regenerating soleus is broader than in mature muscle

Summary In adult rat muscles experimentally exposed to various patterns of activation, expression of myosin heavy chain isoforms changes, but only within a certain adaptive range. It is characteristic and different in fast or slow muscles. This may be due either to different intrinsic properties of the myogenic cells of the two types of muscles or to extrinsic factors. To test these assumptions, either rat soleus or extensor digitorum longus muscles were injured and transplanted to the bed of the extensor digitorum longus muscle. They regenerated and were reinnervated by the extensor digitorum longus nerve. Expression of myosin heavy chain isoforms was demonstrated immunohistochemically and by in situ hybridization, and analysed by SDS-gel electrophoresis. Three months after cross-transplantation, regenerated soleus expressed all adult myosin heavy chain isoforms, including the myosin heavy chain-2B. The latter was detected in about 50% of muscle fibres and contributed about 10–20% of all myosin heavy chains. The same percentage of myosin heavy chain-2B was found in regenerated extensor digitorum longus. In this regard therefore, the adaptive range of the regenerated soleus muscle was not significantly different from that of the extensor digitorum longus regenerating under the same conditions. This indicates that restriction of the adaptive range in a mature soleus muscle is not due to intrinsic properties of its myogenic cells. It is probably imposed by an extrinsic factor leading to irreversible shut-down of individual myosin heavy chain genes. On the other hand, myosin heavy chain-1 expression was significantly greater in the regenerated soleus than in the extensor digitorum longus innervated by the same nerve. Myosin heavy chain-1 and myosin heavy chain-2B were co-expressed in some regenerated soleus muscle fibres.     

Isometric contractions of motor units in self-reinnervated fast and slow twitch muscles of the cat

1. Isometric contractions of motor units have been studied in self-reinnervated soleus and flexor digitorum longus muscles, the motor nerves of which had been transected 6 months earlier.2. The distributions of motor unit tetanic tensions in both muscles were skewed towards large values and showed greater variance than normal: there were motor units which produced more tension and others which developed less tension than in control muscles. Mean tensions of motor units are compared with those of the controls.3. The variance of times to peak of motor units in both muscles was significantly smaller than normal.4. Conduction velocities of axons were slower than normal above the point of nerve section. A number of axons did not functionally cross this point and those that did conducted slowly below the neuroma.5. Many of the correlations seen in normal muscle between axon conduction velocity, motor unit tetanic tension, twitch time to peak and ratio of twitch to tetanic tension were demonstrated in reinnervated muscle.6. We suggest that the pattern of motor unit organization in self-reinnervated muscle can in part be due to random regrowth of axons but is largely produced by specific processes related to axon size which are not identical in fast and slow muscle.     

Beta-endorphin and corticotropin immunoreactivity and specific binding in the neuromuscular system of obese-diabetic mice.

Immunoreactivity for two derivatives of pro-opiomelanocortin, beta-endorphin and alpha-melanocortin (or corticotropin), was demonstrated, using a conventional immunoperoxidase method, in some of the intramuscular nerves in muscle sections from obese diabetic (ob/ob) mice and homozygous lean (+/+) mice. The endplate regions were visualized in the sections by staining for acetylcholinesterase reaction product. The proportion of muscle endplates with beta-endorphin-immunoreactive motor nerves was approximately 2.5-fold higher in soleus and extensor digitorum longus muscles and approximately 1.5-fold higher in the diaphragm of the obese (ob/ob) mice compared to the normal lean mice. The proportion of muscle endplates with alpha-melanotropin-immunoreactive motor nerves was between 30 and 53% lower, depending on the muscle type, in the ob/ob mice compared to the lean mice. The muscles of ob/ob and lean mice were investigated for the presence of specific binding sites for [125I]beta-endorphin and for [125I]corticotropin, using autoradiography. Some muscle fibres in soleus, extensor digitorum longus and diaphragm in both the ob/ob and the lean mice exhibited specific binding sites for the radioactive ligands. The binding sites were distributed over the entire surface in these muscle fibres. In the ob/ob mice the number of muscle fibres with specific [125I]beta-endorphin binding sites was six-fold higher in soleus and approximately 10-fold higher in extensor digitorum longus and diaphragm, than in the corresponding muscles of the lean mice. In contrast, the number of muscle fibres with specific [125I]corticotropin binding sites was similar in obese (ob/ob) and lean mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nerve growth in botulinum toxin poisoned muscles

The rate of growth of motor axon sprouts in muscles fully paralysed with botulinum toxin was studied using the zinc iodide—osmium tetroxide stain. In the mouse soleus and peroneus muscles, the proportions of endplates with nerve terminal sprouts rose to almost 100% in two to three weeks. In both muscles, the initial rate of terminal sprout growth was rather slow—about 3 μm per day. Two to three weeks after the injection the rate had risen to about 15 μm per day. Substantial numbers of polyneuronally innervated muscle fibres could be demonstrated in the soleus, but not the peroneus, by twelve days after the injection. The soleus remained polyneuronally innervated over a year after the injection.The time course of the tension recovery by the blocked soleus nerve was compared with that of the tension development by a fibular nerve implanted into a fully paralysed or completely denervated soleus muscle. The rate of tension recovery by the fibular nerve was the same whether the soleus was denervated or simply blocked. After an initial delay, the recovery of tension by the paralysed soleus nerve followed a course very similar to that of the implanted nerves.The implanted nerve did not affect the initial terminal sprouting of the paralysed soleus endplates. However, after three weeks, sprouts from soleus nerve endplates on many fibular innervated muscle fibres had disappeared. The implanted nerve did not affect the sprouting of soleus endplates on the muscle fibres which it did not innervate. The recovery of tension by the soleus nerves to muscles innervated by implanted nerves was reduced.It is concluded (1) that recovery from paralysis after botulinum toxin poisoning is slow because formation of new extrajunctional synapses is slow; (2) that motor nerve terminals are more readily induced to sprout by changes occurring on their own muscle fibres than by inactivity induced changes in muscle fibres elsewhere in the same muscle; (3) that paralysis of the mouse soleus renders the muscle as receptive to innervation extrajunctionally as does denervation.     

Factors causing different properties at neuromuscular junctions in fast and slow rat skeletal muscles

Neuromuscular junctions on fast and slow skeletal muscle fibers have different properties. Possible reasons for these differences were examined in adult rat soleus (SOL) muscle fibers reinnervated at new ectopic or old denervated sites by fast fibular (FIB) or slow SOL motoneurons. FIB motoneurons formed large ectopic junctions with a high density of nerve terminal varicosities (fast appearance), whereas SOL motoneurons formed small ectopic junctions with a low density of varicosities (slow appearance). Both FIB and SOL motoneurons formed small junctions with a slow appearance when reinnervating old SOL endplates. FIB nerves innervating ectopic sites and SOL nerves reinnervating old sites had the same appearance whether they contacted the SOL fibers alone (single innervation) or together (dual innervation). Continuous stimulation of the FIB nerve at 10 Hz for 3–4 months reduced the size of ectopic FIB and intact extensor digitorum longus (EDL) junctions and caused a modest reduction in density of terminal varicosities in EDL. Junction size and muscle fiber diameter were positively correlated, but the slope describing this relation was steeper for FIB junctions than for SOL junctions. It is concluded that in the present system (1) motoneuron type and not muscle fiber type determines the fast or slow character of the neuromuscular junction, (2) denervated endplates of one type place stable and severe constraints on the termination pattern of reinnervating axons of another type, (3) the appearance of fast EDL junctions undergoes a modest fast to slow transformation when exposed to long-term slow pattern stimulation, and (4) not only the size of the muscle fibers, but also the type and firing pattern of the motoneurons and the spatial constraints at preformed endplates influence the relation between junction size and muscle fiber diameter.     

Innervation by Nerve Implants of “Fast” and “Slow” Skeletal Muscles of the Rat

The time course of innervation by nerve implants of the fast contracting flexor digitorum longus and the slow contracting soleus muscles were studied by the recorcling of isometric twitch tensions in response to stimulation of the implanted nerve and by histochemical visualization of newly-formed end-plates. When a foreign motor nerve was implanted into a muscle 30 days prior to sectioning of the original nerve supply, synaptic contacts were established 4–8 days after the section of the nerve, while, with simultaneous implantation and denervation, 16 days were required for the implanted nerve to innervate the muscle. Implantation of the nerve which normally innervates the flexor digitorum longus muscle into the soleus altered the contraction and relaxation speeds of the soleus muscle towards those of a fast contracting muscle, the change being apparent as soon as 4–8 days following sectioning of the original nerve. In muscles with nerve implants and intact normal innervation hypertrophy occurred, amounting to 20–30 per cent within one month.     

Physiological properties and pattern of innervation of regenerated muscles in the rat

The regeneration of fast and slow muscles was compared following "mincing" and replacement into their own or alien muscle bed. At intervals varying from 2 to 9 weeks the tension developed by the regenerated muscles was assessed and compared to that developed by the muscles from the contralateral unoperated side. This parameter was then taken as an indication of recovery. The regenerated muscles never developed more than half of the tension of the control muscles. Muscles regenerated in the bed of extensor digitorum longus became fast-twitch muscles and muscles regenerated in the bed of soleus became slow-twitch muscles, no matter whether they originated from an extensor digitorum longus or soleus "mince". The regeneration of the muscle tissue in the place of extensor digitorum longus developed better than in the place of soleus. The pattern of innervation of the regenerated muscles was analysed using a combined cholinesterase silver stain. Many of the regenerated fibres had more than one end plate and some end plates more than one axon terminal. These results show that in adult animals muscle redevelopment can occur, but only to a limited extent. Moreover, on reinnervation of regenerated muscle fibres the axons do not assume their original pattern of innervation.     

Comparison of physiological and histochemical properties of motor units after cross-reinnervation of antagonistic muscles in the cat hindlimb

1. Physiological and histochemical properties of the cat ankle extensor muscles, the lateral and medial gastrocnemius, and the soleus were studied after cross-reinnervation by flexor motoneurons. 2. Tibial and common peroneal nerves were cut and cross-united in the popliteal fossa of 2- to 6-mo-old cats. Eighteen to 24 mo later, single motor units were isolated by dissection and stimulation of ventral root filaments and classified into four types: fast-twitch, fatigable (FF), fast-twitch with intermediate fatigue resistance (FI), fast-twitch, fatigue-resistant (FR), and slow, fatigue-resistant (S). Muscle fibers were classified as fast glycolytic (FG), fast, oxidative glycolytic (FOG), and slow oxidative (SO) on the basis of histochemical staining. 3. Although motor-unit force was normally well correlated with the size of the innervating motor axon in the cross-reinnervated muscles, the force of different unit types overlapped considerably. The reinnervated motor units also showed a higher than normal degree of fatigability. 4. The range of muscle unit forces in cross-reinnervated triceps surae muscles was the same as in the normally innervated triceps surae muscles. This range is 2-3 times greater than the flexor muscles, which the common peroneal nerve normally supplies. The range of contraction speed of units in the cross-reinnervated extensor muscles was comparable to that in the flexor muscles, consistent with a motoneuron-specific determination of muscle speed (28). 5. SO and FOG muscle fibers were found in all reinnervated triceps surae muscles, but FG fibers were only found in reinnervated medial gastrocnemius (MG) and lateral gastrocnemius (LG) muscles, consistent with previous findings of the resistance of soleus muscles to complete conversion (10, 16, 20, 21). Type grouping of muscle fibers was characteristic of the reinnervated muscles. 6. Reinnervated SO muscle fibers were larger than the corresponding fibers in normally innervated muscles as were the estimated number of muscle fibers innervated by slow motor axons. Nonetheless, the force generated by the S motor units remained relatively smaller than FR and FF units. The relative contributions of the number, cross-sectional area and specific tension to the force generation of reinnervated motor units are discussed.     

Demonstration of glutamate-like immunoreactivity at rat neuromuscular junctions by quantitative electron microscopic immunocytochemistry

Motor nerve terminals and adjacent structures in the extensor digitorum longus and soleus muscles of young adult rats were examined for their content of glutamate by means of quantitative, electron microscopic immunocytochemistry employing colloidal gold particles as markers. The level of glutamate immunoreactivity was stronger in the extensor digitorum longus terminals than in the soleus terminals. In both muscles the glutamate immunolabelling was stronger in the nerve terminals than in the synaptic clefts and the postsynaptic tissue separating the secondary clefts, but the differences were larger in the extensor digitorum longus than in the soleus muscle. The myofibrils of the soleus muscle were more densely labelled than those in the extensor digitorum longus muscle: The level of immunoreactivity was high in the Schwann cells of both muscles. By comparing the labelling intensity of motor nerve terminals with that of muscle fibres and hippocampal mossy fibres (compartments that have been analysed previously with respect to their glutamate content), the mean concentration of fixed glutamate in the extensor digitorum terminals was estimated to be in the range of 10–20 mmol/l. An association of glutamate immunoreactivity with synaptic vesicles was demonstrated in the most strongly labelled terminals. Whether these epitopes were localized in the interior of the vesicles or at their external surface could not be resolved with the present technique. These data indicate that motor nerve terminals contain glutamate, and that the enrichment of this amino acid is more pronounced in the terminals of the extensor digitorum longus muscle (a fast muscle) than in those of the soleus muscle (a slow muscle). A possible modulatory or trophic role of glutamate in the mammalian neuromuscular junction should be considered.     

Topographic comparison of neuromuscular junctions in mouse slow and fast twitch muscles

The neuromuscular junctions of mammalian slow and fast twitch muscles are activated differently in vivo and show corresponding physiological differences in vitro, but the structural basis or consequences of these differences are relatively unexplored. Therefore, neuromuscular junctions of mouse fast (extensor digitorum longus) and slow (soleus) twitch muscles were compared by use of new scanning and light microscopy techniques. In both muscles, the endplate appeared as an elliptical area raised to a variable extent above the surrounding sarcolemma and containing the primary clefts. In most soleus endplates, this raised surface area was considerably higher and wider and about three times larger than in extensor digitorum longus. In addition, the primary cleft area was about two-fold greater in soleus than in extensor digitorum longus, even though cleft length was the same. The primary clefts formed either an elliptical shape along the outer margin of the endplate with inward-directed branches or a group of relatively rectilinear dendritic branches orthogonally oriented to one another. The latter type was most frequent in soleus and the elliptical type in extensor digitorum longus. Corresponding patterns of nerve terminal arborizations were seen by light microscopy. Although nerve terminal areas were the same in fast and slow muscles, in the former, numerous diverticulae significantly increased the length of the nerve terminal outline. The possible physiological significance of the different synaptic structure of slow and fast muscle is discussed.     

The influence of secretin on the secretion of pepsin in response to acid stimulants in the anaesthetized cat.

1. The problem of selectivity during reinnervation of skeletal muscle fibres was investigated in the rat using the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus muscles and their nerves. 2. After an operation on these nerves permitting them to compete for reinnervation of one or the other muscle (hereafter called Y-union), virtually the total isometric tetanic tension of EDL muscle could be elicited by stimulating the EDL nerve, while stimulating the soleus nerve yielded little or no tension. In the case of the soleus muscle, stimulation of either nerve elicited about half of the total isometric tetanic tension. 3. During the course of reinnervation of these muscles in non-competitive situations, the time course of increase in the ratio of tension elicited by nerve stimulation to that by direct stimulation was slower in the case of soleus nerve reinnervating EDL muscle, compared with cross-reinnervation in the reverse direction or reinnervation of each muscle by its own nerve. 4. Crushing the common peroneal nerve 12 days after a Y-union in an attempt to retard the EDL nerve did not favour reinnervation of the EDL by soleus nerve, but crushing the nerve again or just once at 1 month after the original operation produced substantial partial reinnervation of the EDL by the soleus nerve. 5. It is concluded that soleus nerve fibres form functioning neuromuscular synapses on EDL muscle fibres only with difficulty. The pattern of reinnervation reveals characteristic differences between fast-twitch and slow-twitch muscles on the one hand and between their respective nerves on the other.     

Characteristics of end-plates formed in mouse skeletal muscles reinnervated by their own or by foreign nerves

Morphological and electrophysiological techniques were used to study the neuromuscular junctions of soleus and extensor digitorum longus muscles in normal mice and 6 months after reinnervation by either their original or foreign nerves. In muscles reinnervated by foreign nerves, there were increased incidences of morphological abnormalities, including ultra-terminal axonal sprouting, multiaxonal innervation of end-plates, and ectopic synapse formation, as compared with both normal muscles and muscles reinnervated by their correct nerves. In spite of the morphological abnormalities, however, there was no evidence that the effectiveness of synapses (as estimated from the mean quantal content, m, of end-plate potentials) formed between nerves and inappropriate muscles was impaired. As had also been found in normally innervated muscles, the value of m was again higher in extensor digitorum longus than in soleus following reinnervation by inappropriate nerves. These results suggest that in mammals, when muscles are reinnervated by foreign nerves, mechanisms exist to maintain the efficacy of neuromuscular transmission, in contrast to the situation in amphibians (Sayers and Tonge, 1982: J. Physiol. (Lond.), 330:57-68). The abnormalities observed in this study following reinnervation may be a morphological manifestation of these corrective mechanisms.     

Cross-innervated mammalian skeletal muscle: histochemical, physiological and biochemical observations

1. Cross-innervation of the slow soleus and fast flexor hallucis longus or flexor digitorum longus muscles has been performed in new-born kittens and rabbits and in adult cats.

2. The effects on the histochemical and structural properties of the muscle have been studied and compared with the changes in the contractile properties.

3. Cross-innervation has produced a dramatic change in histochemical pattern in the fast muscles, with the development of areas of muscle fibres indistinguishable from normal soleus muscle. The converse change from the histochemical pattern of slow soleus to that of fast muscle has also occurred, but has been less consistent.

4. It is concluded that the neural influence determining the contractile properties of fast and slow muscle also has a profound controlling influence on the structure and metabolic activity of the muscle fibres.

5. No significant changes could be demonstrated biochemically in the ATPase activities of the fast and slow muscles following cross-innervation.

     

The importance of peripheral changes in determining the sensitivity of striated muscle to depolarizing drugs

1. The sensitivity of the flexor digitorum longus and soleus muscles to depolarizing drugs was tested after cross-union of their respective motor nerves.2. The alien innervation did not affect the sensitivity of either the flexor digitorum longus (FDL) or soleus muscles, which retained their normal characteristic responses to decamethonium and suxamethonium. The time course of muscle contractions was, however, altered by the cross-union operation.3. A considerable increase in sensitivity to depolarizing drugs was shown after de-afferentation and after tenotomy of the soleus muscles. Both these conditions are associated with muscle atrophy.4. It is suggested that hypersensitivity to depolarizing drugs can be expected in any situation where the muscle is undergoing atrophy.     

Effect of thyroid hormones on acetylcholinesterase mRNA levels in the slow soleus and fast extensor digitorum longus muscles of the rat

In the rat, the level of acetylcholinesterase messenger RNA in the typical slow soleus muscles is only about 20-30% of that in the fast extensor digitorum longus muscles. The expression of contractile proteins in muscles is influenced by thyroid hormones and hyperthyroidism makes the slow soleus muscle faster. The influence of thyroid hormones on the levels of acetylcholinesterase messenger RNA level in the slow soleus and fast extensor digitorum longus muscle of the rat was studied in order to examine the effect of thyroid hormones on muscle acetylcholinesterase expression. Hyperthyroidism was induced in rats by daily thyroid hormone injection or thyroid hormone releasing tablet implantation. Hind-limb suspension was applied to produce muscle unloading. Muscle denervation or reinnervation was achieved by sciatic nerve transection or crush. Acetylcholinesterase messenger RNA levels were analyzed by Northern blots and evaluated densitometrically. Hyperthyroidism increased the levels of acetylcholinesterase messenger RNA in the slow soleus muscles close to the levels in the fast extensor digitorum longus. The effect was the same in the unloaded soleus muscles. Acetylcholinesterase expression increased also in the absence of innervation (denervation), in the presence of changed nerve activation pattern (reinnervation), and under enhanced tonic neural activation of the soleus muscle (electrical stimulation). However, the changes were substantially smaller than those observed in the control soleus muscles. Enhancement of acetylcholinesterase expression in the soleus muscles by the thyroid hormones is, therefore, at last in part due to hormonal effect on the muscle itself. On the contrary, increased level of the thyroid hormones had no influence on acetylcholinesterase expression in the normal fast extensor digitorum longus muscles. However, some enhancing influence was apparent whenever the total number of nerve-induced muscle activations per day in the extensor digitorum longus muscle was increased. Thyroid hormones seem to be an independent extrinsic factor of acetylcholinesterase regulation in the slow soleus muscle.     

Effects of cross reinnervation on the energetics of rat skeletal muscle

Experiments were carried out to investigate the changes which occur in the energy production of cross reinnervated fast and slow twitch skeletal muscles. Rat soleus (SOL) and extensor digitorum longus (EDL) muscles were used in myothermic experiments. It was found that the energy production of cross reinnervated skeletal muscle is largely determined by the source of the nervous innervation; as are the dynamic and histological properties of mammalian skeletal muscle. There was an increase in the energy production of crossed soleus muscle and a concomitant reduction in the energy production of crossed EDL. The changes observed correlated well with the measured changes in the force-velocity properties.     

A Case of the Bilateral Duplicate Palmaris Longus Muscles Coupled with the Palmaris Profundus Muscle

The palmaris longus muscle is one of the most variable muscles in human anatomy. During a routine anatomical dissection for medical students at Tottori University, we found duplicate palmaris longus muscles in the bilateral forearms together with the palmaris profundus muscle in the right forearm. The bilateral aberrant palmaris longus muscles were observed at the ulnar side of the palmaris longus muscle and their distal tendons were attached to the flexor retinaculum. The palmaris profundus muscle found in the right forearm was located at the radial side of the flexor digitorum superficialis muscle. The proximal tendon was originated from the anterior surface in the middle of the radius, while the distal tendon coursed radial to the median nerve through the carpal tunnel, finally inserting into the distal part of the flexor retinaculum. Both the palmaris longus and aberrant palmaris longus muscles were innervated by the median nerve. The palmaris profundus muscle was presumably supplied by the median nerve.