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.

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 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.

scholarly journals Muscle-Pair Specific Distribution and Grip-Type Modulation of Neural Common Input to Extrinsic Digit Flexors

2006 ◽  
Vol 96 (3) ◽  
pp. 1258-1266 ◽  
Author(s):  
Sara A. Winges ◽  
Jamie A. Johnston ◽  
Marco Santello
Keyword(s):  
Motor Units ◽  
Middle Finger ◽  
Flexor Digitorum Profundus ◽  
Flexor Muscle ◽  
Common Input ◽  
Single Motor Units ◽  
Specific Distribution ◽  
Neural Input ◽  
Muscle Pair ◽  
Flexor Digitorum

To gain insight into the synergistic control of hand muscles, we have recently quantified the strength of correlated neural activity across motor units from extrinsic digit flexors during a five-digit object-hold task. We found stronger synchrony and coherence across motor units from thumb and index finger flexor muscle compartment than between the thumb flexor and other finger flexor muscle compartments. The present study of two-digit object hold was designed to determine the extent to which such distribution of common input among thumb-finger flexor muscle compartments, revealed by holding an object with five digits, is preserved when varying the functional role of a given digit pair. We recorded normal force exerted by the digits and electrical activity of single motor units from muscle flexor pollicis longus (FPL) and two compartments of the m. flexor digitorum profundus (FDP2 and FDP3; index and middle finger, respectively). Consistent with our previous results from five-digit grasping, synchrony and coherence across motor units from FPL-FDP2 was significantly stronger than in FPL-FDP3 during object hold with two digits [common input strength: 0.49 ± 0.02 and 0.35 ± 0.02 (means ± SE), respectively; peak coherence: 0.0054 and 0.0038, respectively]. This suggests that the distribution of common neural input is muscle-pair specific regardless of grip type. However, the strength of coherence, but not synchrony, was significantly stronger in two- versus five-digit object hold for both muscle combinations, suggesting the periodicity of common input is sensitive to grip type.

Evolutionary adaptations in the flexor digitorum profundus muscle in Tamandua mexicana (Xenarthra, Myrmecophagidae)

2020 ◽  
Author(s):  
Juan Fernando Vélez‐García ◽  
Aura Cristina Arbeláez‐Quiñones ◽  
Karoll Dayanna Montealegre‐Hurtado
Keyword(s):  
Flexor Digitorum Profundus ◽  
Flexor Digitorum ◽  
Flexor Digitorum Profundus Muscle ◽  
Tamandua Mexicana

Anatomic variation of the innervation of the flexor digitorum profundus muscle and its clinical implications

2009 ◽  
Vol 39 (4) ◽  
pp. 498-502 ◽  
Author(s):  
Chang-Seok Oh ◽  
Hyung-Sun Won ◽  
Kyu-Seok Lee ◽  
In-Hyuk Chung ◽  
Seung Min Kim
Keyword(s):  
Anatomic Variation ◽  
Flexor Digitorum Profundus ◽  
Clinical Implications ◽  
Flexor Digitorum ◽  
Flexor Digitorum Profundus Muscle

scholarly journals Common Input to Motor Units of Digit Flexors During Multi-Digit Grasping

2004 ◽  
Vol 92 (6) ◽  
pp. 3210-3220 ◽  
Author(s):  
Sara A. Winges ◽  
Marco Santello
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Flexor Digitorum Profundus ◽  
Flexor Muscle ◽  
Common Input ◽  
Single Motor ◽  
Single Motor Units ◽  
Finger Forces ◽  
Middle Ring ◽  
High Level

The control of whole hand grasping relies on complex coordination of multiple forces. While many studies have characterized the coordination of finger forces and torques, the control of hand muscle activity underlying multi-digit grasping has not been studied to the same extent. Motor-unit synchrony across finger muscles or muscle compartments might be one of the factors underlying the limited individuation of finger forces. Such “unwanted” coupling among finger forces, however, might be desirable when a high level of force coupling is required to prevent object slip during grasping. The goal of this study was to quantify the strength of synchrony between single motor units from extrinsic hand muscles as subjects held a device with a five-digit grasp. During the hold phase, we recorded the normal force exerted by each digit and the electrical activity of single motor units from each of the four divisions of the muscle flexor digitorum profundus (FDP) and one thumb flexor muscle, m. flexor pollicis longus (FPL). The strength of motor-unit synchrony was quantified by the common input strength index (CIS). We found moderate to strong motor-unit synchrony between FPL and the index FDP compartment [CIS: 0.49 ± 0.03 (SE)] and across most FDP compartments (0.34 ± 0.02). Weak synchrony, however, was found between FPL and the middle, ring, and little finger FDP compartments (0.25 ± 0.01). This difference might reflect the larger force contribution of the thumb-index finger pair relative to other thumb-finger combinations in five-digit grasping.

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