Single Extensor Research Articles

A cadaveric study of first dorsal extensor compartment in Africans: Clinical implications

While several reports have been made regarding the anatomic variations in the first dorsal extensor compartment, very few have emanated from Africa. This study looked at this compartment with respect to variations in the superficial branch of the radial nerve and the enclosed tendons. The first dorsal extensor compartment of the hand was studied in 32 formalin preserved adult African cadavers. The superficial branch of the radial nerve emerged from underneath the brachioradialis 8.4cm(sd±2.2cm) proximal to the radial styloid and branched 6.2cm (sd ±1.5cm) proximal to it as well. This nerve along with the cephalic vein or its tributary transversed part of the compartment in all the hands. A double Extensor pollicis longus was found in one hand. Septations were observed in 31.3 %(n=10) of the hands. Abductor pollicis longus tendon was fused in three hands, and had more than one slip in 94% of the hands. A single extensor pollicis brevis tendon was found all dissected hands. Clinical implications of these findings are highlighted in this work.

Controlling of Pneumatic Muscle Actuator Systems by Parallel Structure of Neural Network and Proportional Controllers (PNNP).

This article proposed a novel controller structure to track the non-linear behavior of the pneumatic muscle actuator (PMA), such as the elongation for the extensor actuator and bending for the bending PMA. The proposed controller consists of a neural network (NN) controller laid in parallel with the proportional controller (P). The parallel neural network proportional (PNNP) controllers provide a high level of precision and fast-tracking control system. The PNNP has been applied to control the length of the single extensor PMA and the bending angle of the single self-bending contraction actuator (SBCA) at different load values. For further validation, the PNNP has been applied to control a human–robot shared control system. The results show the efficiency of the proposed controller structure.

Minimally Invasive Muscle Embedding Generates Donor-Cell-Derived Muscle Fibers that Express Desmin and Dystrophin.

The aim of this study was to quantify the extent of donor-cell-derived myogenesis achieved by a novel surgical technique known as Minimally Invasive Muscle Embedding (MIME). Through MIME, we implanted a single extensor digitorum longus muscle from donor mice (N=2) that expressed a red fluorescent protein (RFP), into the left tibialis anterior (TA) muscle of immunodeficient host mice (N=4) that expressed a green fluorescent protein (GFP). Soon after MIME, we injected a myotoxin (barium chloride), into the host TA muscle, to trigger concerted muscle degeneration and regeneration. In lieu of MIME, we performed a SHAM procedure on the right TA muscle of the same set of animals. In MIME-treated muscles, 22%±7% and 78%±7% muscle fibers were RFP+ and GFP+, respectively (mean±standard deviation); and all RFP+ fibers were positive for desmin and dystrophin. Conclusion. We conclude that MIME helps generate muscle fibers of donor origin, in host muscle.

Minimally Invasive Muscle Embedding (MIME), Facilitates the Development of Functional Muscle Fibers of Human Cadaveric Origin, in Host Mice

BACKGROUNDMinimally Invasive Muscle Embedding (MIME), is a technique developed in our laboratory, to facilitate the development of donor‐cell‐derived muscle fibers in a host muscle. MIME involves passing a sterile needle through a host muscle, and then implanting a segment of donor muscle tissue along with its myogenic satellite cells, in the needle track within the host muscle.METHODSWe validated MIME, by implanting a single extensor digitorum longus (EDL) muscle, from donor mice (N=2), which expressed a red fluorescent protein (RFP), into the left tibialis anterior muscle (TA), of immunodeficient host mice (N=4), which expressed a green fluorescent protein (GFP). In the same host mice, we performed a SHAM procedure on the right TA. In another set of host mice, we implanted by MIME, segments of human cadaveric TA (3 days post‐mortem), or performed a SHAM procedure (N=4 per group). We triggered concerted muscle degeneration and regeneration by injecting 1.2% barium chloride (BACL) into the TAs after MIME or SHAM. We collected TAs at 14 days after implanting RFP+ mouse donor muscle, and at 12 weeks after implanting human donor muscle. We performed histological and physiological assays to compare MIME‐ and SHAM‐treated host TA muscles. We studied histological images with Image J software to obtain quantitative data. We performed statistical analyses (ANOVAs) with SigmaStat or SPSS software.RESULTSIn host TAs implanted with RFP+ mouse EDL, 22±4% and 78±4% muscle fibers were RFP+ and GFP+, respectively. There were no RFP+ fibers in SHAM‐treated muscles. All RFP+ fibers were positive for desmin and dystrophin, and 65±4 % fibers were centrally nucleated. Donor‐derived fibers had multiple sarcomeres and nuclear domains in series. In host TAs implanted with human muscle, ~30% of the host muscle was of donor origin (GFP−), and the majority of GFP− fibers were positive for human‐specific markers. The contractile torque produced by MIME and SHAM TAs was not statistically different at 12 weeks post‐MIME, and there was no statistical difference compared to torque produced before MIME or SHAM procedures. Data are reported as Mean±SEM. P<0.05 considered significant.CONCLUSIONThrough MIME, we confirm that, human cadaveric muscle, implanted up to 3 days post‐mortem, can generate donor‐derived muscle fibers that are morphologically and functionally healthy. Our studies are translationally‐relevant; since MIME can be adapted to implant myogenic tissue of human cadaveric origin, to generate donor‐derived muscle fibers in human recipients (example: patients with muscle loss from muscle disease, trauma, or aging), with suitable immunosuppressive and rehabilitative therapies.Support or Funding InformationFunded by a Pilot Grant from the Alliance for Regenerative Rehabilitation Research and Training (AR3T), NIH 1R03HD091648‐01 and 5R03HD091648‐02 from NICHD, and a Faculty Startup Package and FRAP award from Wayne State University, to JAR. De‐identified, cadaveric human muscle tissue, was made available through the Body Bequest Program at Wayne State University. MIME facilitates donorderived myogenesisimageMIME facilitates donorderived myogenesisThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Altered skeletal muscle microtubule-mitochondrial VDAC2 binding is related to bioenergetic impairments after paclitaxel but not vinblastine chemotherapies.

Microtubule-targeting chemotherapies are linked to impaired cellular metabolism, which may contribute to skeletal muscle dysfunction. However, the mechanisms by which metabolic homeostasis is perturbed remains unknown. Tubulin, the fundamental unit of microtubules, has been implicated in the regulation of mitochondrial-cytosolic ADP/ATP exchange through its interaction with the outer membrane voltage-dependent anion channel (VDAC). Based on this model, we predicted that disrupting microtubule architecture with the stabilizer paclitaxel and destabilizer vinblastine would impair skeletal muscle mitochondrial bioenergetics. Here, we provide in vitro evidence of a direct interaction between both α-tubulin and βII-tubulin with VDAC2 in untreated single extensor digitorum longus (EDL) fibers. Paclitaxel increased both α- and βII-tubulin-VDAC2 interactions, whereas vinblastine had no effect. Utilizing a permeabilized muscle fiber bundle preparation that retains the cytoskeleton, paclitaxel treatment impaired the ability of ADP to attenuate H2O2 emission, resulting in greater H2O2 emission kinetics. Despite no effect on tubulin-VDAC2 binding, vinblastine still altered mitochondrial bioenergetics through a surprising increase in ADP-stimulated respiration while also impairing ADP suppression of H2O2 and increasing mitochondrial susceptibility to calcium-induced formation of the proapoptotic permeability transition pore. Collectively, these results demonstrate that altering microtubule architecture with chemotherapeutics disrupts mitochondrial bioenergetics in EDL skeletal muscle. Specifically, microtubule stabilization increases H2O2 emission by impairing ADP sensitivity in association with greater tubulin-VDAC binding. In contrast, decreasing microtubule abundance triggers a broad impairment of ADP's governance of respiration and H2O2 emission as well as calcium retention capacity, albeit through an unknown mechanism.

Novel Design and Position Control Strategy of a Soft Robot Arm

This article presents a novel design of a continuum arm, which has the ability to extend and bend efficiently. Numerous designs and experiments have been done to different dimensions on both types of McKibben pneumatic muscle actuators (PMA) in order to study their performances. The contraction and extension behaviour have been illustrated with single contractor actuators and single extensor actuators, respectively. The tensile force for the contractor actuator and the compressive force for the extensor PMA are thoroughly explained and compared. Furthermore, the bending behaviour has been explained for a single extensor PMA, multi extensor actuators and multi contractor actuators. A two-section continuum arm has been implemented from both types of actuators to achieve multiple operations. Then, a novel construction is proposed to achieve efficient bending behaviour of a single contraction PMA. This novel design of a bending-actuator has been used to modify the presented continuum arm. Two different position control strategies are presented, arising from the results of the modified soft robot arm experiment. A cascaded position control is applied to control the position of the end effector of the soft arm at no load by efficiently controlling the pressure of all the actuators in the continuum arm. A new algorithm is then proposed by distributing the x, y and z-axis to the actuators and applying an effective closed-loop position control to the proposed arm at different load conditions.

Design, implementation and modelling of the single and multiple extensor pneumatic muscle actuators

ABSTRACTThe soft actuator represents a valuable addition to the robotics research area in last two decades. These actuators provide significant features such as lightweight, softness, high force to weight ratio and the ability to form in different shapes. This article presents a new length model to the single extensor pneumatic muscle actuator (PMA) which is depended on the constructed parameters and the air pressure. On the other hand, the tensile force formula of the contractor actuator has been modified to describe the extension force of the extensor PMA. The parallel structure of four extensor actuators is designed and implemented as continuum arm. The bending behaviour of the proposed arm is illustrated and modelled mathematically. The length model of the single extensor actuator has validated by the comparison between the model and the experiment data and then a neural network (NN) control system is applied to control the elongation of the extensor PMA. The kinematics for the proposed continuum arm are presented to describe the bending of the arm and its direction.

Central pattern generators in the turtle spinal cord: selection among the forms of motor behaviors.

Neuronal networks in the turtle spinal cord have considerable computational complexity even in the absence of connections with supraspinal structures. These networks contain central pattern generators (CPGs) for each of several behaviors, including three forms of scratch, two forms of swim, and one form of flexion reflex. Each behavior is activated by a specific set of cutaneous or electrical stimuli. The process of selection among behaviors within the spinal cord has multisecond memories of specific motor patterns. Some spinal cord interneurons are partially shared among several CPGs, whereas other interneurons are active during only one type of behavior. Partial sharing is a proposed mechanism that contributes to the ability of the spinal cord to generate motor pattern blends with characteristics of multiple behaviors. Variations of motor patterns, termed deletions, assist in characterization of the organization of the pattern-generating components of CPGs. Single-neuron recordings during both normal and deletion motor patterns provide support for a CPG organizational structure with unit burst generators (UBGs) whose members serve a direction of a specific degree of freedom of the hindlimb, e.g., the hip-flexor UBG, the hip-extensor UBG, the knee-flexor UBG, the knee-extensor UBG, etc. The classic half-center hypothesis that includes all the hindlimb flexors in a single flexor half-center and all the hindlimb extensors in a single extensor half-center lacks the organizational complexity to account for the motor patterns produced by turtle spinal CPGs. Thus the turtle spinal cord is a valuable model system for studies of mechanisms responsible for selection and generation of motor behaviors. NEW & NOTEWORTHY The concept of the central pattern generator (CPG) is a major tenet in motor neuroethology that has influenced the design and interpretations of experiments for over a half century. This review concentrates on the turtle spinal cord and describes studies from the 1970s to the present responsible for key developments in understanding the CPG mechanisms responsible for the selection and production of coordinated motor patterns during turtle hindlimb motor behaviors.

Single stage soft tissue and extensor tendon reconstruction of upper extremity with antero-lateral thigh free flap- A case report

Soft tissue coverage for traumatic soft tissue loss of upper extremity is challenging with limited local tissues availability. Hence, free tissue transfer is indicated. A patient presented to us with degloving injury of the right dorsum hand and forearm following a road traffic accident. There was large soft tissue defect on the dorsal lateral aspect of the hand and forearm, open comminuted fracture of distal end radius with segmental loss of extensor tendons. After adequate debridement and fracture stabilization with external fixator, soft tissue and extensor tendon reconstruction were performed with conjoined flow-through anterior-lateral thigh and tensor fascia lata free flap. At postoperative three months, there was non union of the distal end of right radius. Flap was re-elevated and non union was corrected with osteotomy, non vascularized bone graft and locking plate. Subsequently, at 1 year follow up revealed limited range of movement at wrist joint (flexion-extension 15 degree), acceptable at metacarpophalangeal of all fingers (hyperextension 15 degree, flexion 60 degree) and interphalangeal joints (PIP joint extension- flexion 0-45 degree, DIP joint extension-flexion 0-15 degree). Hand grip was weak and requires further hand therapy. Anterior lateral thigh flap is a versatile and reliable option for reconstruction of large soft tissue and composite defects of upper extremity with favourable outcome.

The effect of the extensor mechanism on maximum isometric fingertip forces: A numerical study on the index finger

The extensor mechanism is a tendinous network connecting intrinsic and extrinsic muscles of the finger and its function has not yet been fully understood. The goal of this study was to assess the effect of the extensor mechanism on the maximum isometric fingertip forces – a parameter which is essential for grasping. For this purpose, maximum fingertip forces in all directions (i.e. feasible force sets) of two musculoskeletal models of the index finger were compared: the wEM model included a full representation of the extensor mechanism, whereas in the noEM model the extensor mechanism was replaced by a single extensor tendon without connectivity to intrinsic muscles. The feasible force sets were computed in the flexion-extension plane for nine postures. Forces in four predefined directions (palmar, proximal, dorsal, and distal), and the peak resultant forces were evaluated. Averaged forces in all four predefined directions were considerably larger in the wEM model (+187.6%). However, peak resultant forces were slightly lower in the wEM model (−4.3% on average). The general advantage of the wEM model could be explained by co-contraction of intrinsic and extrinsic extensor muscles which allowed reaching larger activation levels of the extrinsic flexors. Only within a narrow range of force directions the co-contraction of intrinsic muscles limited the fingertip forces and lead to lower peak resultant forces in the wEM model. Rather than maximizing peak resultant forces, it appears that the extensor mechanism is a sophisticated tool for increasing maximum fingertip forces over a broad range of postures and force directions – making the finger more versatile during grasping.

Role of synemin, an intermediate filament protein, in adult skeletal muscle (1102.25)

Intermediate filament (IF) related diseases are linked to defects in proteins that are associated with the contractile apparatus of skeletal and cardiac muscle, and with costameres. Synemin is a large IF protein that associates with dystrobrevin, vinculin, and talin at costameres at the sarcolemma of striated muscle, as well as with α‐actinin and desmin at Z disks. Synemin can be expressed in either 210 kDa α‐ or 180 kDa β‐ alternatively spliced forms. We generated mice null for synemin by homologous recombination to study synemin’s function in skeletal muscle. Skeletal muscle in the knock out (syn KO) mouse does not make synemin mRNA or protein. Preliminary characterization of the syn KO mouse suggests that it has a mild skeletal muscle phenotype. The organization of costameres appears to be normal, but the fibers appear smaller than controls. Treadmill running uphill test results was not significantly affected when compared to controls. More notably, we have observed differences in the biomechanical properties of the sarcolemma. Stabilization time of blebs generated by applying fixed suction pressure through a pipette to the surface membrane of single Extensor digitorum longus fibers, were slower in the syn KO than in controls but faster than in desmin KO and mdx fibers, which lack dystrophin. Furthermore, the pressure at which the blebs separated from underlying contractile structures were lower than in controls. These results suggest that the viscoelastic properties of the sarcolemma‐costamere‐myofibril complex are significantly influenced by synemin, but less than by desmin and dystrophin.Grant Funding Source: Supported by APS Postdoctoral Fellowship Physiological Genomics and CONACyT to KGP. By NIH to RJB

El İşaret Parmağının Ekstensörlerinin Anatomik Özellikleri

Objective: Extensor indicis proprius (EIP), the extensor medii proprius (EMP) and the extensor indicis medii proprius (EIMP) are important tendons in the surgery of hand as a graft, apart from performing the function of extension. In cases which require surgical treatment of the hand like trauma, rheumatoid arthritis, ulnar nerve palsy, and hypoplasia of the thenar muscle, the EIP, the EMP and the EIMP are suitable muscles for tendon transfer operations. Material and Methods: The variations of the extensor tendons to the index finger were examined in fifty-four dissected hands. Results: The most common pattern of the tendons was a single extensor digitorum indicis (ED-indicis) and a single EIP. The EIP was observed as a single tendon in 87.03% of the specimens, and as a double tendon in 12.96% of them. The EMP was seen in 24.07% of the specimens. In one hand, the muscle had a shared belly with the EMP and the EIMP. Conclusion: The existence of the supernumerary tendons was more frequently encountered at the ulnar side of the ED-indicis than at the radial side. These extra tendons may be of great value in cases of traumatized hands which require tendinoplasty.

The anatomical variations of the extensor tendons to the dorsum of the hand

To lead a quality life, tendon repair must be performed in a trauma causing damage to the extensor tendon of the hand. The aim of this study is to study the structures that can be used as donor tendons. Fifty-four dissected adult hands were examined to study the pattern of the extensor tendons on the dorsum of the hand. The most common distribution patterns of the extensor tendons of the fingers were as follows: a single extensor indicis proprius (EIP) tendon which inserted ulnar to the extensor digitorum (ED)-index; a single ED-index; a single ED-middle; a single ED-ring; an absent ED-little; a double extensor digiti minimi (EDM), and a single ED-ring to the little finger. The frequency of the number of tendons is as follows: a single (87.03%) EIP, a single ED-index (100%), a single (92.6%) ED-middle, a single (75.9%) ED-ring, and an absent (68.5%) or a single (24.1%) ED-little. A double (88.9%) EDM tendons were seen. The thickest type of juncturae tendinum (JT) is found primarily between the ring and little fingers (90%). Suitable excessive tendon and the thickest JT as donor tendon were found in the fourth intermetacarpal space. The present findings, especially the fourth intermetacarpal space, may explain why incisions on the dorsum of the hand should be large and performed with particular care. It is necessary to have a thorough understanding of the arrangements of the multiple extensor muscles and their junctural connections of the hand when tenoplasty or tendon transfer is required.

The effect of a single haemodialysis session on functional mobility in older adults: a pilot study

To undertake balance and functional mobility assessments in older maintenance haemodialysis patients before and after haemodialysis as a pilot study in order to gain initial data and to assess the feasibility and acceptability of this type of study. Postural sway, three-metre timed "up and go" test (TGUGT), and dynamic single leg extensor power (LEP) were measured before and after a haemodialysis session. Male and female maintenance haemodialysis patients aged over 60 years attending the Nottingham City Hospital. Objective outcome measures were postural sway number and sway path (mm) by balance performance monitor, timed three-metre "up and go" test (s), and leg extensor power (W). Blood pressure and weight reductions were also measured. Subjective assessments of practicality and acceptability were made. Twenty-two patients enrolled. Complete data sets were collected for 14 subjects (11 male, three female). Results were analysed using the Wilcoxon signed ranks test for nonparametric data. There was no significant difference before and after dialysis in postural sway, timed "up and go" or leg extensor power. Eight patients did not complete the study and the reasons are examined. There was no significant single-session effect. Results suggest that haemodialysis patients may be weaker and have reduced postural stability when compared to historical data on comparable undialysed patients. The study was logistically complex and would be difficult to expand using these methods, but the issues merit further consideration.

Functional recovery following manipulation of muscles and sense organs in the stick insect leg

We studied functional recovery of leg posture and walking behaviour in the femur-tibia joint control system of stick insects. Leg extensions in resting animals and during walking are produced by different parts of a single extensor muscle. (a) Ablation of the muscle part responsible for fast movements prevented leg extension during the swing phase. Resting posture remained unaffected. Within a few post-operative days, extension movements recovered, provided that sensory feedback was available. Extension movements were now driven by the muscle part which in intact animals controls the resting posture only. (b) Selective ablation of this (slow) muscle part affected the resting posture, while walking was unaffected. The resting posture partly recovered during subsequent days. To test the range of functional recovery and underlying mechanisms, we additionally transected muscle motor innervation, or we inverted or ablated sensory feedback. We found that recovery was based on both muscular and neuronal mechanisms. The latter required appropriate sensory feedback for the process of recovery, but not for the maintenance of the recovered state. Our results thus indicate the existence of a sensory template that guides recovery. Recovery was limited to a behavioural range that occurs naturally in intact animals, though in different behavioural contexts.

An initial investigation into the possible influence of reactive oxygen species (ROS) in chronic nerve compression injuries and the effects of osteopathic manipulative therapy (OMT)

Introduction Results from our lab indicate that changes in muscle morphology and function caused by nerve compression can be ameliorated by use of muscle energy OMT. Design In attempting to determine the mechanism by which these effects occur, we have conducted experiments to establish whether ROS, known to be generated during neural degeneration, may be involved, and whether or not OMT has its effects by decreasing or helping eliminate ROS in and around the muscle. To do so, we have compared the effects of OMT with those of the antioxidant Ginkgo biloba, a known neuroprotective compound. Methods Rats underwent unilateral chronic sciatic nerve compression (at 100 mmHg) via suture ligation for four, six or eight weeks. Of these experimental animals, four underwent no treatment, four underwent two-times weekly OMT, four were fed Ginkgo biloba (Gb; incorporated into food pellets), and a final group of four received both OMT and Gb. As in previous experiments, OMT included both passive and active muscle energy techniques and effleurage and petrissage. All other methods were the same as previously presented. Animals were euthanized after four, six or eight weeks, and single fast-twitch extensor digitorum longus fibers were dissected and chemically demembranated. As in previous studies, we assessed fiber morphology by direct measurement, and function as the change in force generation caused by the fatigue metabolite inorganic orthophosphate (Pi; (H2PO4−)). Results Under all experimental conditions, there was a tendency for amelioration of the enhanced Pi sensitivity caused by nerve compression, with significant differences among the OMT groups at four, six and eight weeks, with Gb reducing muscle sensitivity to Pi to a lesser degree, and with the reduction being similar at four, six and eight weeks. Differences at four, six and eight weeks remained when OMT was combined with Gb. In all cases, the combined OMT and Gb effects were less than fully additive. OMT, but not Gb, reduced muscle atrophy. Conclusions Present results provide further evidence of the palliative effect of OMT, in the case of muscle morphology and function, in chronic nerve compression syndromes. Also, since the effects of OMT and Gb are not totally additive, we hypothesize that, while OMT and Gb may work via altering oxidative conditions within and around the muscle, in agreement with our previous results, OMT provides an additional ameliorative effect not related to ROS.

Analyses of the differentiation potential of satellite cells from myoD -/-, mdx, and PMP22 C22 mice

BackgroundSporadic and sometimes contradictory studies have indicated changes in satellite cell behaviour associated with the progressive nature of human Duchenne muscular dystrophy (DMD). Satellite cell proliferation and number are reportedly altered in DMD and the mdx mouse model. We recently found that satellite cells in MSVski transgenic mice, a muscle hypertrophy model showing progressive muscle degeneration, display a severe ageing-related differentiation defect in vitro. We tested the hypothesis that similar changes contribute to the gradual loss of muscle function with age in mdx and PMP22 mice, a model of human motor and sensory neuropathy type 1A (HMSN1A).MethodsSingle extensor digitorum longus muscle fibres were cultured from mdx and PMP22 mice and age- and genetic background-matched controls. Mice at several ages were compared with regard to the differentiation of satellite cells, assayed as the proportion of desmin-expressing cells that accumulated sarcomeric myosin heavy chain.ResultsSatellite cells of 2 month, 6 month, and 12 month old mdx mice were capable of differentiating to a similar extent to age-matched wild type control animals in an in vitro proliferation/differentiation model. Strikingly, differentiation efficiency in individual 6 month and 12 month old mdx animals varies to a much higher extent than in age-matched controls, younger mdx animals, or PMP22 mice. In contrast, differentiation of myoblasts from all myoD null mice assayed was severely impaired in this assay system. The defect in satellite cell differentiation that occurs in some mdx animals arises from a delay in differentiation that is not overcome by IGF-1 treatment at any phase of cultivation.ConclusionOverall, a defect in satellite cell differentiation above that arising through normal ageing does not occur in mdx or PMP22 mouse models of human disease. Nonetheless, the impaired differentiation of satellite cells from some mdx animals suggests that additional factors, environmental or epigenetic, may lead to deteriorating muscle repair through poor differentiation of satellite cells in genetically predisposed individuals.

Inorganic phosphate affects the pCa-force relationship more than the pCa-ATPase by increasing the rate of dissociation of force generating cross-bridges in skinned fibers from both EDL and soleus muscles of the rat.

The effect of inorganic phosphate (Pi) on Ca2+ -activation of actomyosin ATPase activity and force in permeabilized (skinned) single extensor digitorum longus (EDL) and soleus muscle fibers of the rat were investigated. Increasing concentrations of Pi decreased force more than ATPase rate at all Ca2+ concentrations and this effect was more pronounced at submaximal Ca2+ -activation. Increasing Pi caused both the normalized pCa-ATPase and pCa-force relationship to be shifted to a higher Ca2+ concentration. At all Ca2+ concentrations ATPase was activated at a lower concentration of Ca2+ than force and this difference in Ca2+ concentration required for the activation of ATPase and force was greater in fast-twitch (EDL) than in slow twitch (soleus) muscle. Soleus muscle pCa-ATPase and pCa-force curves were more sensitive to Ca2+ (pCa50 = 5.97 and 5.89, respectively) than EDL (pCa50 = 5.68 and 5.54, respectively). Finally the shape of the pCa-ATPase and pCa-force curves was similar and not affected by Pi. Analysis shows that Pi increases the rate of dissociation of force generating myosin cross-bridges (ratio of ATPase/force (g(app at all Ca2+ concentration, especially at submaximal Ca2+ -activation levels. Pi effects on g(app) are discussed in terms Pi interacting with the isomerization high force AM*ADP states to form high force transitional AM*ADP*Pi* states which facilitate the dissociation of ADP from AM*ADP. Increasing Ca2+ during Ca2+ -activation of the fibers is associated with a progressive decrease in rate of dissociation of force generating myosin cross-bridges g(app).

Firing Properties of Spinal Interneurons during Voluntary Movement. II. Interactions between Spinal Neurons

The relationship between the activity of pairs of simultaneously recorded spinal interneurons (INs) in the cervical enlargement was studied in five monkeys performing voluntary wrist movements. The tendency for INs to exhibit similar response properties and synchronized firing was tested as a function of physical distance between the cells and their correlational linkages with forearm muscles. Nearby INs tended to have more similar torque and direction turning (signal correlation) and more similar response profiles (e.g., tonic vs phasic firing) than INs that were far apart. This suggests that nearby cells receive common synaptic input. In contrast, the trial-to-trial covariation of rate around the mean rate for all trials (noise correlation) was independent of the distance between the neurons. Furthermore, signal and noise correlation were independent, suggesting different underlying mechanisms. Surprisingly, spike-to-spike correlation between INs was relatively infrequent and weak, as measured by cross-correlation histograms. In contrast, single motor units (SMUs) in forearm muscles fired more synchronously, particularly for SMUs in single extensor muscles. Either common drive to INs is too weak to induce synchronized firing, or there is an active decorrelation mechanism within IN networks.

Motoneurons Have Different Membrane Resistance during Fictive Scratching and Weight Support

The passive membrane properties of motoneurons may be affected in a behavior-specific manner because of differences in synaptic drive during different motor behaviors. To explore this possibility, the changes in input resistance (R(in)) and membrane time constant (tau(m)) of single extensor motoneurons were compared during two different types of motor activities: fictive scratching and fictive weight support. These two activities were selected because the membrane potential of extensor motoneurons follows a very different trajectory during fictive scratching (multiphasic, mostly rhythmic trajectory) and fictive weight support (monophasic, tonic trajectory). The intracellular recordings were performed in vivo in the immobilized, decerebrate cat using QX-314-containing microelectrodes to block action potentials. The R(in) and tau(m) at rest (control) were reduced substantially during all phases of fictive scratching. In contrast, R(in) and tau(m) changed only little during fictive weight support. Such a differential effect on the membrane resistance was observed even in motoneurons in which the peak voltage of the rhythmic depolarization during scratching was similar to the peak voltage of the tonic depolarization during weight support. The differential effect was attributed mainly to a difference in synaptic drive and, in particular, to a larger amount of inhibitory synaptic activity during fictive scratching. The present study demonstrates how the same motoneuron can have a different membrane resistance while participating in two different behaviors. Such tuning of the membrane resistance may provide motoneurons with behavior-specific integrative capabilities that, in turn, could be used advantageously to increase motor performance.