Extramuscular myofascial force transmission also occurs between synergistic muscles and antagonistic muscles

The purpose of the present study was to test the hypothesis that myofascial force transmission may not be limited by compartmental boundaries of a muscle group to synergists. Muscles of the anterior tibial compartment in rat hindlimb as well as of the neighbouring peroneal compartment (antagonistic muscles) were excited maximally. Length–force data, based on proximal lengthening, of EDL, as well as distal lengthening of the tibial muscles (TA + EHL) and the peroneal muscle group (PER) were collected independently, while keeping the other two muscle groups at a constant muscle–tendon complex length. Simultaneously measured, distal and proximal EDL active forces were found to differ significantly throughout the experiment. The magnitude of this difference and its sign was affected after proximal lengthening of EDL itself, but also of the tibial muscle complex and of the peroneal muscle complex. Proximal lengthening of EDL predominantly affected its synergistic muscles within the anterior crural compartment (force decrease <4%). Lengthening of either TA or PER caused a decrease in distal EDL isometric force (by 5–6% of initial force). It is concluded also that mechanisms for mechanical intermuscular interaction extend beyond the limits of muscle compartments in the rat hindlimb. Even antagonistic muscles should not be considered fully independent units of muscular function.

Particular, strong mechanical interaction was found between antagonistic tibial anterior muscle and peroneal muscle complexes: Lengthening of the peroneal complex caused tibial complex force to decrease by approximately 25%, whereas for the reverse a 30% force decrease was found.     

Ultrastructure of incubated muscles

Morphological changes were observed in the peripheral fibres of both rat and rabbit muscles which had been incubated in vitro. These changes occurred rapidly and indicated that degenerative processes were taking place in these muscles. Consequently the morphological and physiological integrity of rat and rabbit muscles incubated in vitro is called into question.     

Contractions of holothurian muscles

Summary In response to quick stretch, contraction is elicited in longitudinal retractor muscles of five tested species of holothurians, and in the pharyngeal retractor ofCucumaria. The effects of amplitude of stretch and rate of stretch are additive. Rates of contraction and repetitiveness of response, and spontaneous rhythmicity (especially in muscles ofLeptosynapta), correlate with mode of life.Contractile responses to stretch are abolished by anesthesia with procaine or magnesium. Responses are enhanced by physostigmine or prostigmine, blocked by d-tubocurarine. Responses to electric shocks persist after block of responses to stretch and after block of spontaneous activity by anesthesia, by cholinergic blockers or by Na replacement. Responses to both stretch and shock are abolished by reducing calcium or by agents which block Ca-conductance.It is postulated (1) that quick stretch stimulates the terminals of cholinergic nerves, (2) that conduction in these nerve fibers is by Na but is TTX resistant, (3) that the nerve endings activate conductance increase for Ca⁺⁺ in muscle fibers which initiate contractions.No muscle potentials were recorded by suction or pressure electrodes and no nexal junctions were observed between muscle fibers. The muscles were well innervated and synaptic endings and some neural somata were seen in the nerve bundles.Thanks are due to Dennis Willows, director and to staff, University of Washington Laboratories, Friday Harbor; to C.L. Singla of the University of Victoria for preparing and examining electron micrographs; to J.L.S. Cobb for commenting on electron micrographs; to Richard Meiss for designing and constructing ramp stretching device. C. Ladd Prosser was supported by NIH grant 5-R01 AM 12768-10 and George O. Mackie by grant no. A 1427, Nat. Sci. and Eng. Res. Council of Canada.     

Vibration activity of muscles

Experimental research of autooscillations of biomechanical links in the equilibrium state was carried out. It is found that the induced vibrations of all the links of biomechanical systems can be described by the equations being true for mechanical oscillator vibrations. With the muscular strain being constant and moment inertia of the biomechanical system changing the energy of mechanical vibrations is constant, but the ratio of kinetic energy of the biomechanical oscillator to oscillation frequency is invariant under the muscular strain changes.     

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

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

Morphogenesis of transverse straited muscles

During the past 50 years there have been significant advances in our understanding of striated muscle development, both from tissue culture studies and from observations of myogenesis in the developing foetus. Experiments, using the distinctive nucleolar marker of quail nuclei, have led to reexamination of the source of the body's muscle masses. Advances have been made in our understanding of the events which occur and mechanisms involved in the formation of multinucleated myofibers from mononucleated myoblasts. Recently, the development of entire muscle organs has been studied. The present review attempts to synthesize the results of both in vivo and in vitro studies of myogenesis, comparing both their similarities and their differences. Attention has been focused on recent advances in our understanding of the source of muscles in the intact foetus, the formation of extrafusal and intrafusal fibers, and the development of the afferent and efferent neuromuscular relationships.     

Transmitter release in botulinum-poisoned muscles

Examination of miniature end-plate potentials (m.e.p.ps) in rat skeletal muscle poisoned in vivo by botulinum toxin type A reveals the presence of two populations of potentials. One population which corresponds to m.e.p.ps in unpoisoned muscles and to quantal end-plate potentials. The frequency of these m.e.p.ps is greatly reduced by botulinum toxin. The second population of m.e.p.ps has quite different characteristics. These m.e.p.ps have a more variable, but generally much larger amplitude, and their time to peak is longer than normal m.e.p.ps. The frequency of these m.e.p.ps increases during poisoning and reaches 0.3-1 Hz after 10-14 days. In addition to the variability in amplitude and time-to-peak these m.e.p.ps differ from those at unpoisoned junctions by being unaffected by procedures which alter extra- or intracellular Ca2+ concentrations. The appearance of this Ca2+-insensitive spontaneous quantal secretion of acetylcholine is apparently not a direct effect of the toxin but secondary to blockade of impulse transmission since it also appears at unpoisoned end-plates when transmission is impaired for other reasons. Procedures which increase the intracellular Ca2+ concentration in nerve terminals restore transmitter release from botulinum toxin poisoned nerves. Furthermore, the block caused by the toxin is very temperature-dependent, a reduction in temperature relieving the block. Since presynaptic Ca2+ currents are unaltered by the toxin it is proposed that the block of transmission is due to a reduction in the calcium content of the nerve terminal to a level where the amount of Ca2+, which normally enters, is insufficient to activate transmitter release.     

Cleaved Slit directs embryonic muscles

The formation of functional musculoskeletal system relies on proper connectivity between muscles and their corresponding tendon cells. In Drosophila, larval muscles are born during early embryonic stages, and elongate toward tendons that are embedded within the ectoderm in later. The Slit/Robo signaling pathway had been implicated in the process of muscle elongation toward tendons. Here we discuss our recent findings regarding the critical contribution of Slit cleavage for immobilization and stabilization of the Slit signal on the tendon cells. Slit cleavage produces 2 polypeptides, the N-terminal Slit-N, which is extremely stable, undergoes oligomerization, and associates with the tendon cell surfaces, and the C-terminal Slit-C, which rapidly degrades. Slit cleavage leads to immobilization of Slit signaling on tendons, leading to a short-range repulsion, which eventually arrest further muscle elongation. Robo2, which is co-expressed with Slit by the tendon cells facilitates Slit cleavage. This activity does not require the cytoplasmic signaling domain of Robo2. We suggest that Robo2-dependent Slit cleavage, and the formation of Slit-N oligomers on the tendon cell surfaces direct muscle elongation, and provide a stop signal for the approaching muscle, through binding to Robo and Robo3 receptors expressed by the muscles.