Motor-Unit Synchrony Within and Across Compartments of the Human Flexor Digitorum Superficialis

2007 ◽  
Vol 97 (1) ◽  
pp. 550-556 ◽  
Author(s):  
Tara L. McIsaac ◽  
Andrew J. Fuglevand
Keyword(s):  
Motor Unit ◽  
Motor Neurons ◽  
Motor Units ◽  
Flexor Digitorum Profundus ◽  
Human Hand ◽  
Flexor Digitorum Superficialis ◽  
Short Term ◽  
Synaptic Inputs ◽  
Muscles Of The Hand ◽  
Flexor Digitorum

An interesting feature of the muscular organization of the human hand is that the main flexors and extensors of the fingers are compartmentalized and give rise to multiple parallel tendons that insert onto all the fingers. Previous studies of motor-unit synchrony in extensor digitorum and flexor digitorum profundus indicated that synaptic input to motor neurons supplying these multitendoned muscles is not uniformly distributed across the entire pool of motor neurons but instead appears to be partially segregated to supply subsets of motor neurons that innervate different muscular compartments. Little is known, however, about the organization of the synaptic inputs to the motor neurons supplying another multitendoned finger muscle, the flexor digitorum superficialis (FDS). Therefore in this study, we estimated the extent of divergence of last-order inputs to FDS motor neurons by measuring the degree of short-term synchrony among motor units within and across compartments of FDS. The degree of synchrony for motor-unit pairs within the same digit compartment was nearly twofold that of pairs of motor units in adjacent compartments and more than fourfold that of pairs in nonadjacent compartments. Therefore like other multitendoned muscles of the hand, last-order synaptic inputs to motor neurons supplying the FDS appear to primarily supply subsets of motor neurons innervating specific finger compartments. Such an organization presumably enables differential activation of separate compartments to facilitate independent movements of the fingers.

scholarly journals Influence of common synaptic input to motor neurons on the neural drive to muscle in essential tremor

2015 ◽  
Vol 113 (1) ◽  
pp. 182-191 ◽  
Author(s):  
Juan A. Gallego ◽  
Jakob L. Dideriksen ◽  
Ales Holobar ◽  
Jaime Ibáñez ◽  
José L. Pons ◽  
...  
Keyword(s):  
Motor Unit ◽  
Motor Neurons ◽  
Synaptic Input ◽  
Motor Units ◽  
Spike Trains ◽  
Neural Drive ◽  
Systematic Analysis ◽  
Synaptic Inputs ◽  
Tremor Frequency ◽  
Unit Spike

Tremor in essential tremor (ET) is generated by pathological oscillations at 4–12 Hz, likely originating at cerebello-thalamo-cortical pathways. However, the way in which tremor is represented in the output of the spinal cord circuitries is largely unknown because of the difficulties in identifying the behavior of individual motor units from tremulous muscles. By using novel methods for the decomposition of multichannel surface EMG, we provide a systematic analysis of the discharge properties of motor units in nine ET patients, with concurrent recordings of EEG activity. This analysis allowed us to infer the contribution of common synaptic inputs to motor neurons in ET. Motor unit short-term synchronization was significantly greater in ET patients than in healthy subjects. Furthermore, the strong association between the degree of synchronization and the peak in coherence between motor unit spike trains at the tremor frequency indicated that the high synchronization levels were generated mainly by common synaptic inputs specifically at the tremor frequency. The coherence between EEG and motor unit spike trains demonstrated the presence of common cortical input to the motor neurons at the tremor frequency. Nonetheless, the strength of this input was uncorrelated to the net common synaptic input at the tremor frequency, suggesting a contribution of spinal afferents or secondary supraspinal pathways in projecting common input at the tremor frequency. These results provide the first systematic analysis of the neural drive to the muscle in ET and elucidate some of its characteristics that determine pathological tremulous muscle activity.

scholarly journals Periodic Modulation of Motor-Unit Activity in Extrinsic Hand Muscles During Multidigit Grasping

2005 ◽  
Vol 94 (1) ◽  
pp. 206-218 ◽  
Author(s):  
Jamie A. Johnston ◽  
Sara A. Winges ◽  
Marco Santello
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Flexor Digitorum Profundus ◽  
Common Input ◽  
Hand Muscles ◽  
Single Motor Units ◽  
Flexor Digitorum ◽  
The Relationship ◽  
Muscle Coherence

We recently examined the extent to which motor units of digit flexor muscles receive common input during multidigit grasping. This task elicited moderate to strong motor-unit synchrony (common input strength, CIS) across muscles (flexor digitorum profundus, FDP, and flexor pollicis longus, FPL) and across FDP muscle compartments, although the strength of this common input was not uniform across digit pairs. To further characterize the neural mechanisms underlying the control of multidigit grasping, we analyzed the relationship between firing of single motor units from these hand muscles in the frequency domain by computing coherence. We report three primary findings. First, in contrast to what has been reported in intrinsic hand muscles, motor units belonging to different muscles and muscle compartments of extrinsic digit flexors exhibited significant coherence in the 0- to 5- and 5- to 10-Hz frequency ranges and much weaker coherence in the higher 10–20 Hz range (maximum 0.0025 and 0.0008, respectively, pooled across all FDP compartment pairs). Second, the strength and incidence of coherence differed considerably across digit pairs. Third, contrary to what has been reported in the literature, across-muscle coherence can be stronger and more prevalent than within-muscle coherence, as FPL–FDP2 (thumb-index digit pair) exhibited the strongest and most prevalent coherence in our data (0.010 and 43% at 3 Hz, respectively). The heterogeneous organization of common input to these muscles and muscle compartments is discussed in relation to the functional role of individual digit pairs in the coordination of multiple digit forces in grasping.

Short-Term Synchronization Between Motor Units in Different Functional Subdivisions of the Human Flexor Digitorum Profundus Muscle

2004 ◽  
Vol 92 (2) ◽  
pp. 734-742 ◽  
Author(s):  
Karen T. Reilly ◽  
Michael A. Nordstrom ◽  
Marc H. Schieber
Keyword(s):  
Motor Units ◽  
Flexor Digitorum Profundus ◽  
Short Term ◽  
Common Input ◽  
Limited Ability ◽  
Motoneuron Pool ◽  
Flexor Digitorum ◽  
Human Nervous System ◽  
Central Factors ◽  
Flexor Digitorum Profundus Muscle

The ability to independently move the digits is limited by peripheral as well as central factors. A central limitation to independent finger movements might arise from the inability of the human nervous system to activate motor units (MUs) that exert force on one finger without also activating MUs that exert force on adjacent fingers. Short-term synchronization between MU pairs is thought to be the result of the two motoneurons receiving common input from last-order neuronal projections. The human flexor digitorum profundus (FDP) muscle contains four subdivisions, one for each of the fingers. We hypothesized that the distribution of MU synchrony within and between subdivisions of FDP might parallel the ability to selectively activate different functional subdivisions within FDP, and the ability to flex one digit independently of another. We found that the degree of MU synchrony indeed was not uniform among the different functional subdivisions of FDP; MUs acting on ulnar digits (d5, d4) were more synchronized than MUs acting on radial digits (d2, d3). Furthermore, synchrony was observed between MU pairs where each unit acted on a different digit and was highest when both units of a pair acted on the least-independent digits (d4, d5). This indicates that the CNS does not exert completely independent control over the different functional subdivisions of FDP. The strength of synchrony appears related to the inability to produce completely independent forces or movements with the digits. These observations reflect widespread divergence of last-order inputs within the FDP motoneuron pool, and we suggest that the organization of the CNS drive to this muscle contributes to the limited ability of humans to flex one digit in isolation from other digits.

scholarly journals Short-term synchrony in diverse motor nuclei presumed to receive different extents of direct cortical input

2012 ◽  
Vol 108 (12) ◽  
pp. 3264-3275 ◽  
Author(s):  
Douglas A. Keen ◽  
Li-Wei Chou ◽  
Michael A. Nordstrom ◽  
Andrew J. Fuglevand
Keyword(s):  
Motor Unit ◽  
Motor Neurons ◽  
Tibialis Anterior Muscle ◽  
Motor Units ◽  
Short Term ◽  
Abductor Hallucis ◽  
Cortical Input ◽  
Abductor Hallucis Muscle ◽  
Human Muscles ◽  
Cortical Inputs

Motor units within human muscles usually exhibit a significant degree of short-term synchronization. Such coincident spiking typically has been attributed to last-order projections that provide common synaptic input across motor neurons. The extent of branched input arising directly from cortical neurons has often been suggested as a critical factor determining the magnitude of short-term synchrony. The purpose of this study, therefore, was to quantify motor unit synchrony in a variety of human muscles differing in the presumed extent of cortical input to their respective motor nuclei. Cross-correlation histograms were generated from the firing times of 551 pairs of motor units in 16 human muscles. Motor unit synchrony tended to be weakest for proximal muscles and strongest for more distal muscles. Previous work in monkeys and humans has shown that the strength of cortical inputs to motor neurons also exhibits a similar proximal-to-distal gradient. However, in the present study, proximal-distal location was not an exclusive predictor of synchrony magnitude. The muscle that exhibited the least synchrony was an elbow flexor, whereas the greatest synchrony was most often found in intrinsic foot muscles. Furthermore, the strength of corticospinal inputs to the abductor hallucis muscle, an intrinsic foot muscle, as assessed through transcranial magnetic stimulation, was weaker than that projecting to the tibialis anterior muscle, even though the abductor hallucis muscle had higher synchrony values compared with the tibialis anterior muscle. We argue, therefore, that factors other than the potency of cortical inputs to motor neurons, such as the number of motor neurons innervating a muscle, significantly affects motor unit synchrony.

scholarly journals Flexor Digitorum Superficialis and Flexor Digitorum Profundus with separated sheaths

2015 ◽  
pp. 199-201
Author(s):  
Seyed Mokhtar Esmaeilnejd Ganji ◽  
Behnam Baghianimoghadam
Keyword(s):  
Clinical Relevance ◽  
Proximal Phalanx ◽  
Clinical Findings ◽  
Flexor Digitorum Profundus ◽  
Human Hand ◽  
Normal Variation ◽  
Case Description ◽  
Flexor Digitorum Superficialis ◽  
Zone Ii ◽  
Flexor Digitorum

Case description: A 25 years old man presented with a laceration on radial side of proximal phalanx of 4th finger (zone II flexor) which was due to cut with glass. Clinical findings: The sheaths of Tendons of flexor digitorum sperficialis and profundus were not the same and each tendon had a separate sheath. Treatment and outcome: The tendons were reconstructed by modified Kessler sutures, after 15 months the patient had a 30 degrees of extension lag even after physiotherapy courses. Clinical relevance: This is the first reported of such normal variation in human hand tendon anatomy.

scholarly journals Common Input to Motor Neurons Innervating the Same and Different Compartments of the Human Extensor Digitorum Muscle

2004 ◽  
Vol 91 (1) ◽  
pp. 57-62 ◽  
Author(s):  
Douglas A. Keen ◽  
Andrew J. Fuglevand
Keyword(s):  
Motor Unit ◽  
Motor Neurons ◽  
Cross Correlation ◽  
Motor Units ◽  
Extensor Digitorum ◽  
Short Term ◽  
Common Input ◽  
Active Motor ◽  
Voluntary Contractions ◽  
Input Strength

Short-term synchronization of active motor units has been attributed in part to last-order divergent projections that provide common synaptic input across motor neurons. The extent of synchrony thus allows insight as to how the inputs to motor neurons are distributed. Our particular interest relates to the organization of extrinsic finger muscles that give rise distally to multiple tendons, which insert onto all the fingers. For example, extensor digitorum (ED) is a multi-compartment muscle that extends digits 2–5. Given the unique architecture of ED, it is unclear if synaptic inputs are broadly distributed across the entire pool of motor neurons innervating ED or segregated to supply subsets of motor neurons innervating different compartments. Therefore the purpose of this study was to evaluate the degree of motor-unit synchrony both within and across compartments of ED. One hundred and forty-five different motor-unit pairs were recorded in the human ED of nine subjects during weak voluntary contractions. Cross-correlation histograms were generated for all of the motor-unit pairs and the degree of synchronization between two units was assessed using the index of common input strength (CIS). The degree of synchrony for motor-unit pairs within the same compartment (CIS = 0.7 ± 0.3; mean ± SD) was significantly greater than for motor-unit pairs in different compartments (CIS = 0.4 ± 0.22). Consequently, last-order synaptic projections are not distributed uniformly across the entire pool of motor neurons innervating ED but are segregated to supply subsets of motor neurons innervating different compartments.

Reduction of Common Synaptic Drive to Ankle Dorsiflexor Motoneurons During Walking in Patients With Spinal Cord Lesion

2005 ◽  
Vol 94 (2) ◽  
pp. 934-942 ◽  
Author(s):  
N. L. Hansen ◽  
B. A. Conway ◽  
D. M. Halliday ◽  
S. Hansen ◽  
H. S. Pyndt ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Motor Unit ◽  
Healthy Subjects ◽  
Motor Units ◽  
Central Peak ◽  
Spinal Cord Lesion ◽  
Short Term ◽  
Physiological Markers ◽  
Synaptic Drive ◽  
Cord Lesion

It is possible to obtain information about the synaptic drive to motoneurons during walking by analyzing motor-unit coupling in the time and frequency domains. The purpose of the present study was to compare motor-unit coupling during walking in healthy subjects and patients with incomplete spinal cord lesion to obtain evidence of differences in the motoneuronal drive that result from the lesion. Such information is of importance for development of new strategies for gait restoration. Twenty patients with incomplete spinal cord lesion (SCL) participated in the study. Control experiments were performed in 11 healthy subjects. In all healthy subjects, short-term synchronization was evident in the discharge of tibialis anterior (TA) motor units during the swing phase of treadmill walking. This was identified from the presence of a narrow central peak in cumulant densities constructed from paired EMG recordings and from the presence of significant coherence between these signals in the 10- to 20-Hz band. Such indicators of short-term synchrony were either absent or very small in the patient group. The relationship between the amount of short-term synchrony and the magnitude of the 10- to 20-Hz coherence in the patients is discussed in relation to gait ability. It is suggested that supraspinal drive to the spinal cord is responsible for short-term synchrony and coherence in the 10- to 20-Hz frequency band during walking in healthy subjects. Absence or reduction of these features may serve as physiological markers of impaired supraspinal control of gait in SCL patients. Such markers could have diagnostic and prognostic value in relation to the recovery of locomotion in patients with central motor lesions.

OUTCOME OF TRACTION TENOLYSIS IN OPEN TRIGGER FINGER RELEASE — A RETROSPECTIVE REVIEW

Hand Surgery ◽  
2013 ◽  
Vol 18 (03) ◽  
pp. 375-379 ◽  
Author(s):  
Muntasir Mannan Choudhury ◽  
Shian Chao Tay
Keyword(s):  
Flexor Tendon ◽  
Group Versus ◽  
Trigger Finger ◽  
Flexor Digitorum Profundus ◽  
Flexor Digitorum Superficialis ◽  
Active Motion ◽  
Total Active Motion ◽  
The Mean ◽  
Flexor Digitorum ◽  
A1 Pulley

Surgical treatment for trigger finger involves division of the A1 pulley. Some surgeons perform an additional step of traction tenolysis by sequentially bringing the flexor digitorum superficialis and flexor digitorum profundus tendons out of the wound gently with a Ragnell retractor. There is currently no study which states whether flexor tendon traction tenolysis should be routinely performed or not. The objective of this study is to compare the outcome in patients who have traction tenolysis performed (A group) versus those who did not have traction tenolysis (B group) performed. It was noted that even though the mean total active motion (TAM) for the B group in our study was lower preoperatively, it was consistently higher than the A group in all the 3 post-operative visits demonstrating a better outcome in the B group. Even though it was not statistically significant, our data also showed that patients with traction tenolysis appeared to have more postoperative pain compared to those without.

Sliding Position of the Flexor Tendons Relative to the Hook of Hamate in CT Scans

2019 ◽  
Vol 24 (01) ◽  
pp. 72-75
Author(s):  
Kenji Goto ◽  
Kiyohito Naito ◽  
Yoichi Sugiyama ◽  
Nana Nagura ◽  
Ayaka Kaneko ◽  
...  
Keyword(s):  
Flexor Tendon ◽  
Tendon Injury ◽  
Ct Scans ◽  
Flexor Digitorum Profundus ◽  
Flexor Digitorum Superficialis ◽  
Ulnar Side ◽  
Flexor Tendon Injury ◽  
Hook Of Hamate ◽  
Flexor Digitorum ◽  
Little Finger

Background: The aim of this study was to assess the height of nonunion formation injuring the ulnar-side finger flexor tendon, the positional relationship between the hook of the hamate and little finger flexor tendon was evaluated on CT scans. Methods: The subjects were 20 healthy patients (40 hands) (14 males and 6 females, mean age: 28 years old). Their hands were imaged in extension and flexion of the fingers on CT. The position of the little finger flexor tendon was determined regarding the height of the hook of the hamate as 100%. Results: The heights of the flexor digitorum profundus tendons were 46 ± 6% in extension and 44 ± 9% in flexion, and those of the flexor digitorum superficialis tendons were 87 ± 8% in extension and 91 ± 9% in flexion. Conclusions: Our study suggested that 40% of the base of the hook of the hamate does not contact with the flexor tendon, suggesting that flexor tendon injury is unlikely to occur in that region.

scholarly journals Bilateral Variation of Forearm Flexor Muscles - A Case Report and Clinical Significance

2012 ◽  
Vol 01 (01) ◽  
pp. 040-043
Author(s):  
D. Malar ◽  
Keyword(s):  
Middle Finger ◽  
Flexor Digitorum Profundus ◽  
Flexor Digitorum Superficialis ◽  
Flexor Carpi Ulnaris ◽  
Close Proximity ◽  
Flexor Muscles ◽  
Male Cadaver ◽  
Forearm Flexor Muscles ◽  
Flexor Digitorum ◽  
Forearm Flexor

AbstractDuring routine dissection, bilateral multiple variations of forearm flexor muscles were observed in a male cadaver. The variations were a) an additional belly arising from the coronoid process of ulna, distal to the origin of ulnar head of flexor digitorum superficialis, passing deep to flexor digitorum superficialis and joining the tendon of flexor digitorum profundus to the middle finger; b) an additional belly arising from the distal part of flexor carpi ulnaris and passing superficial to ulnar nerve and ulnar vessels in the Guyon's canal and c) the origin of second lumbricals from the profundus tendon in the carpal tunnel. An aberrant muscle may stimulate a ganglion or a soft tissue tumor or if in close proximity to a nerve, it may cause pressure neuritis. Identification of these variations is important in defining the anatomical features for clinical diagnosis and surgical procedures.

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