gamma motor neurons


Summary: Motor neurons which activate the contractile regions of intrafusal SKELETAL MUSCLE FIBERS, thus adjusting the sensitivity of the MUSCLE SPINDLES to stretch. Gamma motor neurons may be "static" or "dynamic" according to which aspect of responsiveness (or which fiber types) they regulate. The alpha and gamma motor neurons are often activated together (alpha gamma coactivation) which allows the spindles to contribute to the control of movement trajectories despite changes in muscle length.

Top Publications

  1. Hui K, Kucera J, Henderson J. Differential sensitivity of skeletal and fusimotor neurons to Bcl-2-mediated apoptosis during neuromuscular development. Cell Death Differ. 2008;15:691-9 pubmed
    ..axonal loss in bcl-2-null mice demonstrates that, in contrast to the great majority of alpha motor neurons, gamma motor neurons exhibit a unique dependence upon bcl-2 for survival...
  2. Whitehead J, Keller Peck C, Kucera J, Tourtellotte W. Glial cell-line derived neurotrophic factor-dependent fusimotor neuron survival during development. Mech Dev. 2005;122:27-41 pubmed
  3. Shneider N, Brown M, Smith C, Pickel J, Alvarez F. Gamma motor neurons express distinct genetic markers at birth and require muscle spindle-derived GDNF for postnatal survival. Neural Dev. 2009;4:42 pubmed publisher
    b>Gamma motor neurons (gamma-MNs) selectively innervate muscle spindle intrafusal fibers and regulate their sensitivity to stretch...
  4. Limanaqi F, Gambardella S, Lazzeri G, Ferrucci M, Ruggieri S, Fornai F. Revisiting the gamma loop in ALS. Arch Ital Biol. 2017;155:118-130 pubmed publisher
    ..These latter in fact, differently from gamma motor neurons, are a direct monosynaptic target of proprioceptive fibers...
  5. Cueva Rolón R, Delgado Lezama R, Raya J, Raya M, Tecuanhuey R, Muñoz Martínez E. Sustained firing of alpha and gamma hind limb motoneurons induced by stimulation of the pudendal nerve. J Neurophysiol. 2002;88:3232-42 pubmed
    ..The increased excitatory inflow would depolarize alpha MNs and allow bistable MN firing; Panc would decrease this inflow by blocking transmission to the spindle fibers. ..
  6. Mileusnic M, Brown I, Lan N, Loeb G. Mathematical models of proprioceptors. I. Control and transduction in the muscle spindle. J Neurophysiol. 2006;96:1772-88 pubmed
    ..This model will be useful in understanding the role of the muscle spindle and its fusimotor control during both natural and pathological motor behavior. ..
  7. Walsh L, Smith J, Gandevia S, Taylor J. The combined effect of muscle contraction history and motor commands on human position sense. Exp Brain Res. 2009;195:603-10 pubmed publisher
    ..We propose that central signals combine with afferent signals to determine limb position and that multiple sources of information are weighted according to their reliability. ..
  8. Rossi Durand C. Proprioception and myoclonus. Neurophysiol Clin. 2006;36:299-308 pubmed
  9. Taylor A, Ellaway P, Durbaba R, Rawlinson S. Distinctive patterns of static and dynamic gamma motor activity during locomotion in the decerebrate cat. J Physiol. 2000;529 Pt 3:825-36 pubmed
    ..The term 'interrupted' discharge is suggested as a useful description. The timing of this discharge was shown to be appropriate for sensitising the primary afferents to detect the onset of stretch. ..

More Information


  1. Durbaba A, Taylor R, Rawlinson S, Ellaway P. Static fusimotor action during locomotion in the decerebrated cat revealed by cross-correlation of spindle afferent activity. Exp Physiol. 2003;88:285-96 pubmed
    ..The synchrony of muscle spindle afferent discharge is discussed in relation to estimates of the numbers of spindles contacted by individual gammaS-efferents. ..
  2. Sjölander P, Johansson H, Djupsjöbacka M. Spinal and supraspinal effects of activity in ligament afferents. J Electromyogr Kinesiol. 2002;12:167-76 pubmed
  3. Jones K, Wessberg J, Vallbo A. Proprioceptive feedback is reduced during adaptation to a visuomotor transformation: preliminary findings. Neuroreport. 2001;12:4029-33 pubmed
    ..These preliminary results suggest that the CNS reduces the sensory signals arising from muscle spindles perhaps as a means of resolving the conflict between visual and proprioceptive feedback during the task. ..
  4. Capra N, Hisley C, Masri R. The influence of pain on masseter spindle afferent discharge. Arch Oral Biol. 2007;52:387-90 pubmed
    ..The implication of these results will be considered in light of current theories on the relationship between jaw muscle pain and oral motor function. ..
  5. Nagaoka M, Kakuda N. [Neural mechanisms underlying spasticity]. Brain Nerve. 2008;60:1399-408 pubmed
    ..We have discussed the changes in membrane properties caused by presynaptic inhibition, reciprocal Ia inhibitory function, recurrent inhibition, and autogenic Ib inhibition as the other candidate spinal mechanisms for spasticity. ..
  6. Lalancette Hébert M, Sharma A, Lyashchenko A, Shneider N. Gamma motor neurons survive and exacerbate alpha motor neuron degeneration in ALS. Proc Natl Acad Sci U S A. 2016;113:E8316-E8325 pubmed publisher
    ..This study establishes the resistance of γ-MNs as a general feature of ALS mouse models and demonstrates that synaptic excitation of MNs within a complex circuit is an important determinant of relative vulnerability in ALS. ..
  7. Ahmed Z. Modulation of gamma and alpha spinal motor neurons activity by trans-spinal direct current stimulation: effects on reflexive actions and locomotor activity. Physiol Rep. 2016;4: pubmed publisher
    Spontaneous and evoked spinal activities interact to set the characteristics of emergent motor responses. Gamma motor neurons have feedforward and feedback functions in motor control, which are crucial for transforming motor commands ..
  8. Beaudet M, Yang Q, Cadau S, Blais M, Bellenfant S, Gros Louis F, et al. High yield extraction of pure spinal motor neurons, astrocytes and microglia from single embryo and adult mouse spinal cord. Sci Rep. 2015;5:16763 pubmed publisher
    ..Functional astrocytes and microglia and small gamma motor neurons can be purified at the same time...
  9. Watts R, Schuldiner O, Perrino J, Larsen C, Luo L. Glia engulf degenerating axons during developmental axon pruning. Curr Biol. 2004;14:678-84 pubmed
    ..Our study reveals a key role for glia in the removal of axon fragments during developmental axon pruning. ..
  10. Durbaba R, Taylor A, Ellaway P, Rawlinson S. Classification of longissimus lumborum muscle spindle afferents in the anaesthetized cat. J Physiol. 2006;571:489-98 pubmed
    ..The significance of this relatively high proportion of b2c-type spindle primary afferents is discussed in relation to the specialized postural function of the back muscles. ..
  11. Fallon J, Carr R, Gregory J, Proske U. Summing responses of cat soleus muscle spindles to combined static and dynamic fusimotor stimulation(1). Brain Res. 2001;888:348-355 pubmed
    ..340 (+/-0.020 S.E.M.). These findings were interpreted in terms of a model of the muscle spindle where responses to dynamic fusimotor stimulation arise at one impulse generating site, and static fusimotor responses arise at another. ..
  12. Wang K, Arendt Nielsen L, Svensson P. Capsaicin-induced muscle pain alters the excitability of the human jaw-stretch reflex. J Dent Res. 2002;81:650-4 pubmed
    ..Increased sensitivity of the fusimotor system during acute muscle pain could be one likely mechanism to explain the findings. ..
  13. Lin C, Crago P. Structural model of the muscle spindle. Ann Biomed Eng. 2002;30:68-83 pubmed
    ..The current model provides a powerful tool for simulation studies of neuromusculoskeletal systems, and demonstrates the feasibility of using a structural approach to model complex neurophysiological systems. ..
  14. Starikov A. Functional state of segmental motoneurons in Wilson-Konovalov hepatocerebral dystrophy. Neurosci Behav Physiol. 1997;27:648-52 pubmed
    ..Changes in H-reflex and M-response parameters demonstrated functional rearrangement of the movement analyzer after stereotaxic surgery. The functional states of the alpha- and gamma-systems are discussed. ..
  15. Murphy P. Adaptive fusimotor reflex control in the decerebrate cat. Brain Res. 1999;821:38-49 pubmed
    ..The results are discussed in relation to cutaneous effects on gamma-motoneurones which are suggested to form an adaptive control system. ..
  16. Gandevia S, Wilson L, Inglis J, Burke D. Mental rehearsal of motor tasks recruits alpha-motoneurones but fails to recruit human fusimotor neurones selectively. J Physiol. 1997;505 ( Pt 1):259-66 pubmed
    ..Similar changes occur with preparation for movement following a cue. It is likely that mental rehearsal usually involves unintentional performance of the planned motor task. ..
  17. Biro A, Griffin L, Cafarelli E. Reflex gain of muscle spindle pathways during fatigue. Exp Brain Res. 2007;177:157-66 pubmed
    ..These results provide evidence that the gain of the gamma loop is increased during fatigue, indicating possible peripheral neural compensation to the motor neuron pool in order to preserve force output. ..
  18. Feldman A, Levin M. The equilibrium-point hypothesis--past, present and future. Adv Exp Med Biol. 2009;629:699-726 pubmed publisher
    ..These aspects as well as how motor learning occurs are subjects of further development of the TCT hypothesis. ..
  19. Durbaba R, Taylor A, Ellaway P, Rawlinson S. The influence of bag2 and chain intrafusal muscle fibers on secondary spindle afferents in the cat. J Physiol. 2003;550:263-78 pubmed
    ..The results do not suggest that it could also usefully control stretch sensitivity. ..
  20. Roy R, Matsumoto A, Zhong H, Ishihara A, Edgerton V. Rat alpha- and gamma-motoneuron soma size and succinate dehydrogenase activity are independent of neuromuscular activity level. Muscle Nerve. 2007;36:234-41 pubmed
  21. Johansson H, Sjölander P, Sojka P, Wenngren B. Effects of L-DOPA on fusimotor control of triceps surae muscle spindles in the cat. Neurosci Res. 1995;22:307-14 pubmed
    ..The possible role of monoaminergic descending control of fusimotor neurones in the regulation of muscle tone, tremor and rigidity is discussed. ..
  22. Murphy P, Hammond G. Reversal of fusimotor reflex responses during locomotion in the decerebrate cat. Exp Physiol. 1997;82:837-58 pubmed
    ..The results are discussed in relation to the role and reflex control of the fusimotor system. ..
  23. Wang K, Arendt Nielsen L, Svensson P. Excitatory actions of experimental muscle pain on early and late components of human jaw stretch reflexes. Arch Oral Biol. 2001;46:433-42 pubmed
    ..A change in the sensitivity of the fusimotor system during muscle pain is suggested as an explanation. ..
  24. Parra J, Kalitzin S, Iriarte J, Blanes W, Velis D, Lopes da Silva F. Gamma-band phase clustering and photosensitivity: is there an underlying mechanism common to photosensitive epilepsy and visual perception?. Brain. 2003;126:1164-72 pubmed
    ..This novel finding leads us to postulate that a pathological deviation of normally occurring synchronization of gamma oscillations, underlying perceptional processes, mediates the epileptic transition in PSE. ..
  25. Jankowska E, Gladden M, Czarkowska Bauch J. Modulation of responses of feline gamma-motoneurones by noradrenaline, tizanidine and clonidine. J Physiol. 1998;512 ( Pt 2):521-31 pubmed
    ..5. The results indicate that some antispastic effects of clonidine and tizanidine may be due to the depression of group II-evoked responses of gamma-motoneurones, resulting in weaker responses of muscle spindles to muscle stretches. ..
  26. Knutson G. The role of the gamma-motor system in increasing muscle tone and muscle pain syndromes: a review of the Johansson/Sojka hypothesis. J Manipulative Physiol Ther. 2000;23:564-72 pubmed
    ..Further research into the effects of metabolites of muscle contraction and their effects on muscle tone is recommended. Research into subluxation/joint dysfunction in light of the Johansson/Sojka hypothesis is recommended. ..
  27. Ma W, Vacca Galloway L. Reduced branching and length of dendrites detected in cervical spinal cord motoneurons of Wobbler mouse, a model for inherited motoneuron disease. J Comp Neurol. 1991;311:210-22 pubmed
    ..The small neurons (presumably a mixed population of gamma-motoneurons, interneurons, and Renshaw cells) possess dendrites and spines that seem to be less affected, and instead show signs of sprouting. ..
  28. Thunberg J, Hellstrom F, Sjölander P, Bergenheim M, Wenngren B, Johansson H. Influences on the fusimotor-muscle spindle system from chemosensitive nerve endings in cervical facet joints in the cat: possible implications for whiplash induced disorders. Pain. 2001;91:15-22 pubmed
  29. Gregory J, Wood S, Proske U. An investigation of the Jendrassik manoeuvre. Acta Physiol Pharmacol Bulg. 2001;26:171-5 pubmed
    ..A remaining, untested mechanism is the modulation of oligosynaptic pathways that may contribute to the largely monosynaptic reflex response. ..
  30. Taylor A, Durbaba R, Ellaway P, Rawlinson S. Static and dynamic gamma-motor output to ankle flexor muscles during locomotion in the decerebrate cat. J Physiol. 2006;571:711-23 pubmed
    ..The dynamic gamma pattern sensitizes the primary afferents to detect the onset of muscle lengthening and to detect departures from the intended movement trajectory. ..
  31. Gladden M, Maxwell D, Sahal A, Jankowska E. Coupling between serotoninergic and noradrenergic neurones and gamma-motoneurones in the cat. J Physiol. 2000;527 Pt 2:213-23 pubmed
  32. Kobayashi Y, Okuda T, Fujioka Y, Matsumura G, Nishimura Y, Haga T. Distribution of the high-affinity choline transporter in the human and macaque monkey spinal cord. Neurosci Lett. 2002;317:25-8 pubmed
    ..Human CHT is thus a novel cholinergic marker, which not only labels cholinergic neurons, but also reveals their heterogeneity. ..
  33. Proske U. The discovery of two types of fusimotor fibre by Peter Matthews. Exp Physiol. 2008;93:50-2 pubmed publisher
  34. Thunberg J, Ljubisavljevic M, Djupsjöbacka M, Johansson H. Effects on the fusimotor-muscle spindle system induced by intramuscular injections of hypertonic saline. Exp Brain Res. 2002;142:319-26 pubmed
    ..Predominantly static fusimotor neurones were activated. The possible role of the fusimotor-muscle spindle system in altered motor control during experimentally induced muscle pain is discussed. ..
  35. Rossi Durand C. The influence of increased muscle spindle sensitivity on Achilles tendon jerk and H-reflex in relaxed human subjects. Somatosens Mot Res. 2002;19:286-95 pubmed
    ..The possibility that a mental computation task may also operate by reducing the level of presynaptic inhibition is discussed on the basis of H-reflex facilitation. ..
  36. Gladden M, Matsuzaki H. Static gamma-motoneurones couple group Ia and II afferents of single muscle spindles in anaesthetised and decerebrate cats. J Physiol. 2002;543:273-88 pubmed
  37. Bae Y, Choi B, Lee M, Lee H, Park K, Zhang L, et al. Quantitative ultrastructural analysis of glycine- and gamma-aminobutyric acid-immunoreactive terminals on trigeminal alpha- and gamma-motoneuron somata in the rat. J Comp Neurol. 2002;442:308-19 pubmed
  38. Allen T, Ansems G, Proske U. Evidence from proprioception of fusimotor coactivation during voluntary contractions in humans. Exp Physiol. 2008;93:391-8 pubmed
    ..The distribution of errors is therefore seen to be a reflection of fusimotor recruitment thresholds. For elbow flexors most, but not all, fusimotor fibres appear to be recruited by 10% of a maximal contraction. ..
  39. Durbaba R, Taylor A, Ellaway P, Rawlinson S. Modulation of primary afferent discharge by dynamic and static gamma motor axons in cat muscle spindles in relation to the intrafusal fibre types activated. J Physiol. 2001;532:563-74 pubmed
    ..5. The results are discussed in relation to the ways in which the gamma-motor system may be used in natural movements. ..
  40. Gregory J, Wood S, Proske U. An investigation into mechanisms of reflex reinforcement by the Jendrassik manoeuvre. Exp Brain Res. 2001;138:366-74 pubmed
    ..While this confirms the previously prevailing view, none of the lingering uncertainties associated with the methods used now remains. ..
  41. Burke R. Comparison of alternative designs for reducing complex neurons to equivalent cables. J Comput Neurosci. 2000;9:31-47 pubmed
    ..This was the case in the presence of a somatic shunt as well as when membrane resistivity was uniform. ..
  42. Powis R, Gillingwater T. Selective loss of alpha motor neurons with sparing of gamma motor neurons and spinal cord cholinergic neurons in a mouse model of spinal muscular atrophy. J Anat. 2016;228:443-51 pubmed publisher
    ..Taken together, these findings indicate that α-MNs are uniquely vulnerable among cholinergic neuron populations in the SMA mouse spinal cord, with γ-MNs and other cholinergic neuronal populations being largely spared. ..
  43. Awasaki T, Ito K. Engulfing action of glial cells is required for programmed axon pruning during Drosophila metamorphosis. Curr Biol. 2004;14:668-77 pubmed
    ..We therefore propose that neuron-glia interaction is essential for the precisely coordinated axon-pruning process during Drosophila metamorphosis. ..
  44. Tock Y, Ljubisavljevic M, Thunberg J, Windhorst U, Inbar G, Johansson H. Information-theoretic analysis of de-efferented single muscle spindles. Biol Cybern. 2002;87:241-8 pubmed
    ..67 bits/spike. A simple muscle-spindle simulation model was analyzed with the same method, emphasizing the important part played by the intrafusal fiber mechanical properties in information transmission. ..
  45. Tock Y, Inbar G, Steinberg Y, Ljubisavljevic M, Thunberg J, Windhorst U, et al. Estimation of muscle spindle information rate by pattern matching and the effect of gamma system activity on parallel spindles. Biol Cybern. 2005;92:316-32 pubmed
    ..The results indicate that the gamma system has an important role in enhancing information transmission from ensembles of MSs to the spinal cord. ..
  46. Ito T, Hioki H, Nakamura K, Kaneko T, Iino S, Nojyo Y. Some gamma-motoneurons contain gamma-aminobutyric acid in the rat cervical spinal cord. Brain Res. 2008;1201:78-87 pubmed publisher
    ..Since we detected neither GABAA nor GABAB receptors in the TBM by RT-PCR, the function of the GABA-containing gamma-motoneurons remains unclear. ..
  47. Tanaka M, Owens N, Nagashima K, Kanosue K, McAllen R. Reflex activation of rat fusimotor neurons by body surface cooling, and its dependence on the medullary raphe. J Physiol. 2006;572:569-83 pubmed
    ..It may underlie the increased muscle tone that precedes overt shivering, and could also serve to amplify shivering. Like several other cold-defence responses, this reflex depends upon neurons in the rostral medullary raphé. ..
  48. Perlmutter J, Thach W. Writer's cramp: questions of causation. Neurology. 2007;69:331-2 pubmed
  49. Bent L, Bolton P, Macefield V. Vestibular inputs do not influence the fusimotor system in relaxed muscles of the human leg. Exp Brain Res. 2007;180:97-103 pubmed
    ..We conclude that this dynamic vestibular input was not sufficient to recruit gamma motoneurones, which are known to have little spontaneous activity in relaxed human muscles. ..
  50. Herrmann C, Munk M, Engel A. Cognitive functions of gamma-band activity: memory match and utilization. Trends Cogn Sci. 2004;8:347-55 pubmed
    ..Furthermore, it assumes that late gamma-band activity reflects the readout and utilization of the information resulting from this match. ..
  51. Murphy P. Tonic and phasic discharge patterns in toe flexor gamma-motoneurons during locomotion in the decerebrate cat. J Neurophysiol. 2002;87:286-94 pubmed
    ..The FHL units peaked with the plantar flexor alphas. The FDL neurons generally peaked before alpha activity even began. ..
  52. Taylor A, Durbaba R, Ellaway P, Rawlinson S. Patterns of fusimotor activity during locomotion in the decerebrate cat deduced from recordings from hindlimb muscle spindles. J Physiol. 2000;522 Pt 3:515-32 pubmed
  53. Schalow G. Phase and frequency coordination between neuron firing as an integrative mechanism of human CNS self-organization. Electromyogr Clin Neurophysiol. 2005;45:369-83 pubmed
    ..There is indication that relative phase and frequency coordination is an integrative mechanism for the self-organization of the neuronal networks of the human central nervous system (CNS). ..