Spinal Motoneurons

  • Robert Burke


In a sense, motoneurons are arguably the most important class of neurons in the central nervous system (CNS) because without them, we could neither move nor breathe. Over a century ago, the great English physiologist, Sir Charles Sherrington, recognized that “… at the termination of every reflex arc we find a final neurone, the ultimate conductive link to an effector organ, gland or muscle.” Sherrington named these final neurons “motor neurons” (or motoneurons in most papers today) and called them “the final common path” that receives information from many sources both within and outside of the central nervous system, integrating this information and transmitting it to the muscle fibers that they innervate. Since Sherrington’s time, motoneurons have been extensively studied because of their critical role in the control of all movement in both invertebrate and vertebrate animals. In a real sense, motoneurons are one of only a very few categories of millions of neurons in the central nervous system (CNS) that have a clearly defined function – to cause activation of muscle fibers.


Amyotrophic Lateral Sclerosis Motor Unit Spinal Muscular Atrophy Medial Gastrocnemius Motor Axon 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Further Reading

  1. Alvarez FJ, Dewey DE, Harrington DA, Fyffe REW (1997) Cell-type specific organization glycine receptor clusters in the mammalian spinal cord. J Comp Neurol 379:150–170PubMedCrossRefGoogle Scholar
  2. Alvarez F, Pearson J, Harrington D, Dewey D, Torbeck L, Fyffe R (1998) Distribution of 5-hydroxtryptamine-immunoreative boutons on alpha-motoneurons in the lumbar spinal cord of adult cats. J Comp Neurol 393:69–83PubMedCrossRefGoogle Scholar
  3. Alvarez FJ, Villalba RM, Zerda R, Schneider SP (2004) Vesicular glutamate transporters in the spinal cord, with special references to sensory primary afferent synapses. J Comp Neurol 472:257–280PubMedCrossRefGoogle Scholar
  4. Binder MD, Mendell LM (1990) The segmental motor system. Oxford University Press, New York, 397 pGoogle Scholar
  5. Binder MD, Heckman CJ, Powers RK (1996) The physiological control of motoneuron activity. In: Rowell LB, Shepherd JT (eds) Handbook of physiology sect 12 exercise: regulation and integration of multiple systems. American Physiological Society, New York, pp 3–53Google Scholar
  6. Brännström T (1993) Quantitative synaptology of functionally different types of cat medial gastrocnemius alpha-Motoneurons. J Comp Neurol 330(3):439–454PubMedCrossRefGoogle Scholar
  7. Brownstone R (2006) Beginning at the end: repetitive firing properties in the final common pathway. Prog Neurobiol 78:156–172PubMedCrossRefGoogle Scholar
  8. Brownstone RM, Krawitz S, Jordan LM (2010) Reversal of the late phase of spike frequency adaptation in cat spinal motoneurons during fictive locomotion. J Neurophysiol 105:1045–1050PubMedCrossRefGoogle Scholar
  9. Burke RE (1967) The composite nature of the monosynaptic excitatory postsynaptic potential. J Neurophysiol 30:1114–1137PubMedGoogle Scholar
  10. Burke RE (1968a) Firing patterns of gastrocnemius motor units in the decerebrate cat. J Physiol (Lond) 196:631–645Google Scholar
  11. Burke RE (1968b) Group Ia synaptic input to fast and slow twitch motor units of cat triceps surae. J Physiol (Lond) 196:605–630Google Scholar
  12. Burke RE (1981) Motor units: anatomy, physiology and functional organization. In: Brooks VB (ed) Handbook of physiology, sect 1: the nervous system, vol II motor control, part 1. American Physiological Society, Washington, DC, pp 345–422Google Scholar
  13. Burke RE, Glenn LL (1996) Horseradish peroxidase study of the spatial and electrotonic distribution of group Ia synapses on type-identified ankle extensor motoneurons of the cat. J Comp Neurol 372:465–485PubMedCrossRefGoogle Scholar
  14. Burke RE, Tsairis P (1973) Anatomy and innervation ratios in motor units of cat gastrocnemius. J Physiol (Lond) 234:749–765Google Scholar
  15. Burke RE, Fedina L, Lundberg A (1971) Spatial synaptic distribution of recurrent and group Ia inhibitory systems in cat spinal motoneurones. J Physiol (Lond) 214:305–326Google Scholar
  16. Burke RE, Levine DN, Tsairis P, Zajac FE (1973) Physiological types and histochemical profiles in motor units of the cat gastrocnemius. J Physiol (Lond) 234:723–748Google Scholar
  17. Burke RE, Rymer WZ, Walsh JV (1976) Relative strength of synaptic input from short latency pathways to motor units of defined type in cat medial gastrocnemius. J Neurophysiol 39:447–458PubMedGoogle Scholar
  18. Burke RE, Strick PL, Kanda K, Kim CC, Walmsley B (1977) Anatomy of medial gastrocnemius and soleus motor nuclei in cat spinal cord. J Neurophysiol 40:667–680PubMedGoogle Scholar
  19. Burke RE, Dum RP, Fleshman JW, Glenn LL, Lev-Tov A, O’Donovan MJ, Pinter MJ (1982) An HRP study of the relation between cell size and motor unit type in cat ankle extensor motoneurons. J Comp Neurol 209:17–28PubMedCrossRefGoogle Scholar
  20. Carp JS (1992) Physiological properties of primate lumbar motoneurons. J Neurophysiol 68(4):1121–1132PubMedGoogle Scholar
  21. Coombs JS, Eccles JC, Fatt P (1955a) The electrical properties of the motoneurone membrane. J Physiol (Lond) 130:291–325Google Scholar
  22. Coombs JS, Eccles JC, Fatt P (1955b) Excitatory synaptic actions in motoneurons. J Physiol (Lond) 130:374–395Google Scholar
  23. Creed RS, Denny-Brown D, Eccles JC, Liddell EGT, Sherrington CS (1932) Reflex activity of the spinal cord. Oxford University Press, LondonGoogle Scholar
  24. Cullheim S, Fleshman JW, Glenn LL, Burke RE (1987) Membrane area and dendritic structure in type-identified triceps surae alpha-motoneurons. J Comp Neurol 255:68–81PubMedCrossRefGoogle Scholar
  25. Dasen J, Jessell T (2009) HOX networks and the origins of motor neuron diversity. Curr Top Dev Biol 88:169–200PubMedCrossRefGoogle Scholar
  26. Eccles JC (1957) The physiology of nerve cells. The Johns Hopkins Press, BaltimoreGoogle Scholar
  27. Eccles JC (1964) The physiology of synapses. Academic, New YorkCrossRefGoogle Scholar
  28. ElBasiouny S, Schuster J, Heckman C (2010) Persistent inward currents in spinal motoneurons: important for normal function but potentially harmful after spinal cord injury and in amyotrophic lateral scerosis. Clin Neurophysiol 121:1669–1679PubMedCrossRefGoogle Scholar
  29. Emonet-Denand F, Jami L, Laporte Y (1975) Skeletofusimotor axons in hind-limb muscles of the cat. J Physiol (Lond) 249:153–166Google Scholar
  30. Fleshman JW, Munson JB, Sypert GW (1981a) Homonymous projection of individual group Ia-fibers to physiologically characterized medial gastrocnemius motoneurons in the cat. J Neurophysiol 46:1339–1348PubMedGoogle Scholar
  31. Fleshman JW, Munson JB, Sypert GW, Friedman WA (1981b) Rheobase, input resistance, and motor-unit type in medial gastrocnemius motoneurons in the cat. J Neurophysiol 46:1326–1338PubMedGoogle Scholar
  32. Fleshman JW, Segev I, Burke RE (1988) Electrotonic architecture of type-identified alpha-motoneurons in the cat spinal cord. J Neurophysiol 60:60–85PubMedGoogle Scholar
  33. Fyffe REW (1990) Evidence for separate morphological classes of Renshaw cells in the cat’s spinal cord. Brain Res 536(1–2):301–304PubMedCrossRefGoogle Scholar
  34. Fyffe REW (1991) Spatial distribution of recurrent inhibitory synapses on spinal motoneurons in the cat. J Neurophysiol 65(5):1134–1149PubMedGoogle Scholar
  35. Garnett R, Stephens JA (1981) Changes in the recruitment threshold of motor units produced by cutaneous stimulation in man. J Physiol (Lond) 311:463–473Google Scholar
  36. Gauthier GF, Burke RE, Lowey S, Hobbs AW (1983) Myosin isozymes in normal and cross-reinnervated cat skeletal muscle fibers. J Cell Biol 97:756–771PubMedCrossRefGoogle Scholar
  37. Gossard J-P, Floeter MK, Kawai Y, Burke RE, Chang T, Schiff SJ (1994) Fluctuations of excitability in the monosynaptic reflex pathway to lumbar motoneurons in the cat. J Neurophysiol 72:1227–1239PubMedGoogle Scholar
  38. Granit R (1970) The basis of motor control. Academic, New York, p 346Google Scholar
  39. Hashizume K, Kanda K, Burke RE (1988) The medial gastrocnemius motor nucleus in the rat: age-related changes in the number and size of motoneurons. J Comp Neurol 269:425–430PubMedCrossRefGoogle Scholar
  40. Henneman E, Mendell LM (1981) Functional organization of motoneuron pool and its inputs. In: Brooks VB (ed) Handbook of physiology, sect I, vol II, The nervous system, part 1. American Physiological Society, Bethesda, pp 423–507Google Scholar
  41. Hounsgaard J, Hultborn H, Jespersen B, Kiehn O (1984) Intrinsic membrane properties causing a bistable behaviour of α-motoneurons. Exp Brain Res 55:391–394PubMedCrossRefGoogle Scholar
  42. Howell JN, Fuglevand AJ, Walsh ML, Bigland-Ritchie B (1995) Motor unit activity during isometric and concentric-eccentric contractions of the human first dorsal interosseous muscle. J Neurophysiol 74:901–904PubMedGoogle Scholar
  43. Kanda K, Hashizume K (1989) Changes in properties of the medial gastrocnemius motor units in aging rats. J Neurophysiol 61:737–746PubMedGoogle Scholar
  44. Kanda K, Burke RE, Walmsley B (1977) Differential control of fast and slow twitch motor units in the decerebrate cat. Exp Brain Res 29:57–74PubMedCrossRefGoogle Scholar
  45. Kanning KC, Kaplan A, Henderson CE (2010) Motor neuron diversity in development and disease. Annu Rev Neurosci 33:409–440PubMedCrossRefGoogle Scholar
  46. Kernell D (1965a) High-frequency repetitive firing of cat lumbosacral motoneurones stimulated by long-lasting injected currents. Acta Physiol Scand 65:74–86CrossRefGoogle Scholar
  47. Kernell D (1965b) The limits of firing frequency in cat lumbosacral motoneurones possessing different time course of afterhyperpolarization. Acta Physiol Scand 65:87–100CrossRefGoogle Scholar
  48. Laporte Y, Emonet-Denand F, Jami L (1981) The skeletofusimotor or β-innervation of mammalian muscle spindles. Trends NeuroSci 4:97–99CrossRefGoogle Scholar
  49. Lee RH, Heckman CJ (1998a) Bistability in spinal motoneurons in vivo: systematic variations in rhythmic firing patterns. J Neurophysiol 80:572–582PubMedGoogle Scholar
  50. Lee RH, Heckman CJ (1998b) Bistability in spinal motoneurons in vivo: systematic variations in persistent inward currents. J Neurophysiol 80:583–593PubMedGoogle Scholar
  51. Li Y, Bennett DJ (2003) Persistent sodium and calcium currents cause plateau potentials in motoneurons of chronic spinal rats. J Neurophysiol 90:857–869PubMedCrossRefGoogle Scholar
  52. Liddell EGT, Sherrington CS (1925) Recruitment and some other factors of reflex inhibition. Proc Roy Soc Ser B 97:488–518CrossRefGoogle Scholar
  53. Matthews PBC (1981) Muscle spindles: their messages and their fusimotor supply. In: Brookhart JM, Mountcastle VB (eds) Handbook of physiology, sect 1: The nervous system, vol II Motor control, part 1. American Physiological Society, Bethesda, pp 189–228Google Scholar
  54. McDonagh JC, Binder MD, Reinking RM, Stuart DG (1980) Tetrapartite classification of motor units of cat tibialis anterior. J Neurophysiol 44:696–712PubMedGoogle Scholar
  55. Mendell LM, Henneman E (1971) Terminals of single Ia fibers: location, density, and distribution within a pool of 300 homonymous motoneurons. J Neurophysiol 34:171–187PubMedGoogle Scholar
  56. Mitchell CS, Lee RH (2011) The dynamics of somatic input processing in spinal motoneurons in vivo. J Neurophysiol 105:1170–1178PubMedCrossRefGoogle Scholar
  57. Moschovakis AK, Burke RE, Fyffe REW (1991) The size and dendritic structure of HRP-labeled gamma motoneurons in the cat spinal cord. J Comp Neurol 311:531–545PubMedCrossRefGoogle Scholar
  58. Murray K, Stephens M, Ballou E, Heckman C, Bennett D (2011) Motoneuron excitability and muscle spasms are regulated by 5-HT2B and 5-HT2C receptor activity. J Neurophysiol 105:731–748PubMedCrossRefGoogle Scholar
  59. Nardone A, Romano C, Schieppati M (1989) Selective recruitment of high-threshold human motor units during voluntary isotonic lengthening of active muscles. J Physiol (Lond) 409:451–471Google Scholar
  60. Nelson PG, Burke RE (1967) Delayed depolarization in cat spinal motoneurons. Exp Neurol 17:16–26PubMedCrossRefGoogle Scholar
  61. Prather BD, Clark BD, Cope TC (2002) Firing rate modulation of motoneurons activated by cutaneous and muscle receptor afferents in the decerebrate cat. J Neurophysiol 88:1867–1879PubMedGoogle Scholar
  62. Rall W (1977) Core conductor theory and cable properties of neurons. In: Kandel ER (ed) The nervous system, vol 1, Cellular biology of neurons, part I. American Physiological Society, Washington, pp 39–97Google Scholar
  63. Rank MM, Murray KC, Stephens MJ, D’Amico J, Gorassini MA, Bennett DJ (2011) Transmission and muscle spasms after chronic spinal cord injury. J Neurophysiol 105:410–422PubMedCrossRefGoogle Scholar
  64. Ranvier L (1874) De quelques faits relatifs à l’histologie et à la physiologie des muscles striés. Arch Physiol Norm Pathol 1:5–18Google Scholar
  65. Romanes G (1964) The motor pools of the spinal cord. Prog Brain Res 11:93–119PubMedCrossRefGoogle Scholar
  66. Sherrington C (1947) The integrative action of the nervous system. Yale University Press, New Have, 413 pGoogle Scholar
  67. Smith JL, Betts B, Edgerton VR, Zernicke RF (1980) Rapid ankle extension during paw shakes: selective recruitment of fast ankle extensors. J Neurophysiol 43:612–620PubMedGoogle Scholar
  68. Van de Graaff KM, Frederick EC, Williamson RG, Goslow GE Jr (1977) Motor units and fiber types of primary ankle extensors of the skunk Mephitis mephitis. J Neurophysiol 40:1424–1431Google Scholar
  69. Walmsley B, Hodgson JA, Burke RE (1978) Forces produced by medial gastrocnemius and soleus muscles during locomotion in freely moving cats. J Neurophysiol 41:1203–1216PubMedGoogle Scholar
  70. Zagoraiou L, Akay T, Martin J, Brownstone R, Jessell T, Miles G (2009) A cluster of cholinergic premotor interneurons modulates mouse locomotor activity. Neuron 64:645–662PubMedCrossRefGoogle Scholar
  71. Zajac FE, Faden JS (1985) Relationship among recruitment order, axonal conduction velocity, and muscle-unit properties of type-identified motor units in cat plantaris muscle. J Neurophysiol 53:1303–1322PubMedGoogle Scholar
  72. Zengel JE, Reid SA, Sypert GW, Munson JB (1985) Membrane electrical properties and prediction of motor-unit type of cat medial gastrocnemius motoneurons in the cat. J Neurophysiol 53:1323–1344PubMedGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2013

Authors and Affiliations

  1. 1.The Laboratory of Neural ControlNINDS National Institutes of HealthEl PradoUSA

Personalised recommendations