They receive an excitatory collateral from the alpha neuron's axon as they emerge from the motor root, and are thus "kept informed" of how vigorously that neuron is firing.
They send an inhibitory axon to synapse with the cell body of the initial alpha neuron and/or an alpha motor neuron of the same motor pool.
In this way, the Renshaw cell action represents a negative feedback mechanism. A Renshaw cell may be supplied by more than one alpha motor neuron collateral and it may synapse on multiple motor neurons.
Although during embryonic development the Renshaw cells lack synapses from the dorsal root, prenatal and postnatal stages show the development of dorsal root originating synapses, which are functional and stimulate action potentials. But these decrease during development while acetylcholine motor axons begin to synapse and proliferate with Renshaw cells, ultimately being primarily stimulated by the motor neurons.[1]
The Renshaw cells are ultimately excited by multiple antidromic motor neuron axons, where the majority of axons originate from synergist motor neurons, and in turn the Renshaw cell synapses with multiple neurons, eliciting IPSP in alpha motor, 1a inhibitory interneurons and gamma motor neurons. The antidromic collateral circuit back to the triggering motor neuron is known as “recurrent inhibition”. This homonymous inhibition is not universal. Whereas most initial experiments have been done on cats, it has been found that in man that proximal muscles of the hand and foot do not have homonymous inhibition. Heteronymous inhibition has been found to be dominant in the leg compared to the arm, where antagonist muscles work simultaneously. (Renshaw cells are activated by gamma motor neurons, but to a lesser extent). The Renshaw cells not only synapse with homonymous and heteronymous nerves, but also with the Ia interneurones, which are stimulated by the Ia afferents from the same muscle group activated by the motor neurons, which have an inhibitory effect on the antagonist muscle group. This “recurrent facilitation” causes reduced inhibition of the reciprocal inhibition of the Ia interneuron of the antagonist group (Baret et al.; 2003), which may in turn also be inhibited by signals from the corticospinal tract.[2] It has been shown that:[3][4][5]
Recurrent inhibition is depressed during strong voluntary contractions (presumably due to inhibition of the Reshaw cell by descending input).
Renshaw cells are more inhibited at the same level during a dynamic contraction compared with sustained contraction.
Renshaw cells are facilitated during weak voluntary contractions.
Renshaw cells are facilitated during co-activation of antagonists.
The Renshaw cells may also be inhibited by both proprioceptive dorsal root afferents],[6][7] antidromic ventral axons[8] as well as “descending” inhibition.[9][10] The hyperpolarization of Renshaw cells by afferent and descending neurons have been shown to be caused by the release of glycine, but GABA may also hyperpolarize the Renshaw cell - for a prolonged time relative to glycine. It has also been shown that glycine is the inhibitory transmitter released by the Renshaw cells.[11][12]
In essence the Renshaw cells regulate the firing of the alpha motor neuron leaving the ventral horn. Conceptually they remove “noise” by dampening the firing frequency of over-excited neurons with a negative feedback loop, which prevents weakly excited alpha motor neurons from firing. Descending spinal cord nerves in turn regulate the Renshaw cells.
The rate of discharge of the Renshaw cell is broadly proportional to the rate of discharge of the associated motor neuron(s), and the rate of discharge of the motor neuron(s) is broadly inversely proportional to the rate of discharge of the Renshaw cell(s). Renshaw cells thus act as "limiters," or "governors," on the alpha motor neuron system, thus helping to prevent muscular damage from tetanus.
Renshaw cells utilize the neurotransmitter glycine as an inhibitory substance that synapses on the alpha motor neurons.
Clinical significance
Renshaw cells are also the target of the toxin of Clostridium tetani, a Gram positive, spore-forming anaerobic bacterium that lives in the soil, and causes tetanus. When wounds are contaminated with C. tetani, the toxin travels to the spinal cord where it inhibits the release of glycine, an inhibitory neurotransmitter, from Renshaw cells. As a result, alpha motor neurons become hyperactive, and muscles constantly contract.
Strychnine poison also specifically acts on these cell's ability to control alpha motor neuron firing by binding to the glycine receptors on the alpha motor neuron and thus muscles continually contract and may prove fatal if the diaphragm is involved.
History
The concept of the Renshaw cells was postulated by Birdsey Renshaw (1911–1948),[13] when it was discovered that with antidromic signals from a motor neuron running collaterally back via the ventral root into the spinal cord, there were interneurons firing with a high frequency, resulting in inhibition. Later work by Eccles et al.,[14] provided evidence that these interneurons, which they called “Renshaw Cells,” are stimulated by acetylcholine from motor neurons (nicotinic receptor). Previous work by Renshaw[15] and Lloyd[16][17] had shown that this antidromic inhibition resembled direct inhibition from spinal nerves but resulted in relatively longer inhibition of 40-50 ms (compared to 15 ms). The antidromic stimulation of the nerve fiber also resulted in action potentials in the cell bodies of the motor neurons along with hyperpolarization of other groups of motor neurons. In the event where the initial stimulation of the motor neuron originated in a spinal tract the Renshaw cell spike occurred during the declining phase of the initial motor neuron soma spike giving an indication of the source and sequence of stimulation of the Renshaw cell.
References
^George Z. Mentis, Valerie C. Siembab, Ricardo Zerda, Michael J. O'Donovan, and Francisco J. Alvarez, Primary Afferent Synapses on Developing and Adult Renshaw Cells. The J.of Neuroscience, 2006, 26(51):13297-13310
^ Mazzocchio R, Rossi A, Rothwell JC. Depression of Renshaw recurrent inhibition by activation of corticospinal fibres in human upper and lower limb. J Physiol (Lond) 1994; 481: 487–9
^H. Hultborn, E. Pierrot-Deseilligny.Changes in recurrent inhibition during voluntary soleus contractions in man studied by an H-Reflex Technique. J. Phyeiol. 1979, 297, pp. 229–251.
^Iles JF, Pardoe J. Changes in transmission in the pathway of heteronymous spinal recurrent inhibition from soleus to quadriceps motor neurons during movement in man. Brain 1999; 122: 1757–64
^Nielsen J, Pierrot-Deseilligny E. Evidence of facilitation of soleus-coupled Renshaw cells during voluntary co-contraction of antagonistic ankle muscles in man. J Physiol (Lond) 1996; 493: 603–11
^Wilson VJ, Talbot WH, Kato M Inhibitory convergence upon Renshaw cells. Journal of neurophysiology. 1964;27:1063-1079.
^R. W. Ryall, M. F. Piercey, and C. Polosa. Intersegmental and intrasegmental distribution of mutual inhibition of Renshaw cells. J Neurophysiol 34: 700-, 1971
^RYALL, R. W. Renshaw cell mediated inhibition of Renshaw cells: patterns of excitation and inhibition from impulses in motor axon collaterals. J.Neurophysiol. 1970, 33, 257-270
^R. Granit, J. Haase, and L. T. Rutledge. Recurrent inhibition in relation to frequency of firing and limitation of discharge rate of extensor motoneurones. J. Physiol. 1960 December; 154(2): 308–328.
^J Haase, J van der Meulen. Effects of supraspinal stimulation on Renshaw cells belonging to extensor motoneurones. Journal of neurophysiology. 10/1961; 24:510-20
^D R Curtis, C J Game, D Lodge, and R M McCulloch. A pharmacological study of Renshaw cell inhibition. J. Physiol. 1976 June; 258(1): 227–242
^Victor J. Wilson & William H. Talbot. Integration at an Inhibitory Interneurone: Inhibition of Renshaw Cells. Nature 1963 200, 1325–1327
^Renshaw B. Central effects of centripetal impulses in axons of spinal ventral roots. J Neurophysiol 1946 9:191–204
^Eccles JC, Fatt P, Koketsu K. Cholinergic and inhibitory synapses in a pathway from motor-axon collaterals to motoneurones. J. Physiol. 1954;126:524–562.
^Renshaw B. Influence of discharge of motoneurons upon excitation of neighboring motoneurons. J Neurophysiol 1941 4:167
^Lloyd, D. P. C.. Facilitation and inhibition of spinal motoneurons, J.Neurophysiol.,1946, 9,421.
^ Lloyd, D. P. C., After-currents, after-potentials, excitability, and ventral root electrotonus in spinal motoneurons, J.gen. Physiol..,1951,35 ,289
renshaw, cell, inhibitory, interneurons, found, gray, matter, spinal, cord, associated, ways, with, alpha, motor, neuron, they, receive, excitatory, collateral, from, alpha, neuron, axon, they, emerge, from, motor, root, thus, kept, informed, vigorously, that,. Renshaw cells are inhibitory interneurons found in the gray matter of the spinal cord and are associated in two ways with an alpha motor neuron They receive an excitatory collateral from the alpha neuron s axon as they emerge from the motor root and are thus kept informed of how vigorously that neuron is firing They send an inhibitory axon to synapse with the cell body of the initial alpha neuron and or an alpha motor neuron of the same motor pool Renshaw cellDetailsNeurotransmitterGlycineIdentifiersMeSHD066293NeuroLex IDnifext 113FMA86787Anatomical terms of neuroanatomy edit on Wikidata In this way the Renshaw cell action represents a negative feedback mechanism A Renshaw cell may be supplied by more than one alpha motor neuron collateral and it may synapse on multiple motor neurons Contents 1 Function 2 Clinical significance 3 History 4 References 5 External linksFunction EditAlthough during embryonic development the Renshaw cells lack synapses from the dorsal root prenatal and postnatal stages show the development of dorsal root originating synapses which are functional and stimulate action potentials But these decrease during development while acetylcholine motor axons begin to synapse and proliferate with Renshaw cells ultimately being primarily stimulated by the motor neurons 1 The Renshaw cells are ultimately excited by multiple antidromic motor neuron axons where the majority of axons originate from synergist motor neurons and in turn the Renshaw cell synapses with multiple neurons eliciting IPSP in alpha motor 1a inhibitory interneurons and gamma motor neurons The antidromic collateral circuit back to the triggering motor neuron is known as recurrent inhibition This homonymous inhibition is not universal Whereas most initial experiments have been done on cats it has been found that in man that proximal muscles of the hand and foot do not have homonymous inhibition Heteronymous inhibition has been found to be dominant in the leg compared to the arm where antagonist muscles work simultaneously Renshaw cells are activated by gamma motor neurons but to a lesser extent The Renshaw cells not only synapse with homonymous and heteronymous nerves but also with the Ia interneurones which are stimulated by the Ia afferents from the same muscle group activated by the motor neurons which have an inhibitory effect on the antagonist muscle group This recurrent facilitation causes reduced inhibition of the reciprocal inhibition of the Ia interneuron of the antagonist group Baret et al 2003 which may in turn also be inhibited by signals from the corticospinal tract 2 It has been shown that 3 4 5 Recurrent inhibition is depressed during strong voluntary contractions presumably due to inhibition of the Reshaw cell by descending input Renshaw cells are more inhibited at the same level during a dynamic contraction compared with sustained contraction Renshaw cells are facilitated during weak voluntary contractions Renshaw cells are facilitated during co activation of antagonists The Renshaw cells may also be inhibited by both proprioceptive dorsal root afferents 6 7 antidromic ventral axons 8 as well as descending inhibition 9 10 The hyperpolarization of Renshaw cells by afferent and descending neurons have been shown to be caused by the release of glycine but GABA may also hyperpolarize the Renshaw cell for a prolonged time relative to glycine It has also been shown that glycine is the inhibitory transmitter released by the Renshaw cells 11 12 In essence the Renshaw cells regulate the firing of the alpha motor neuron leaving the ventral horn Conceptually they remove noise by dampening the firing frequency of over excited neurons with a negative feedback loop which prevents weakly excited alpha motor neurons from firing Descending spinal cord nerves in turn regulate the Renshaw cells The rate of discharge of the Renshaw cell is broadly proportional to the rate of discharge of the associated motor neuron s and the rate of discharge of the motor neuron s is broadly inversely proportional to the rate of discharge of the Renshaw cell s Renshaw cells thus act as limiters or governors on the alpha motor neuron system thus helping to prevent muscular damage from tetanus Renshaw cells utilize the neurotransmitter glycine as an inhibitory substance that synapses on the alpha motor neurons Clinical significance EditRenshaw cells are also the target of the toxin of Clostridium tetani a Gram positive spore forming anaerobic bacterium that lives in the soil and causes tetanus When wounds are contaminated with C tetani the toxin travels to the spinal cord where it inhibits the release of glycine an inhibitory neurotransmitter from Renshaw cells As a result alpha motor neurons become hyperactive and muscles constantly contract Strychnine poison also specifically acts on these cell s ability to control alpha motor neuron firing by binding to the glycine receptors on the alpha motor neuron and thus muscles continually contract and may prove fatal if the diaphragm is involved History EditThe concept of the Renshaw cells was postulated by Birdsey Renshaw 1911 1948 13 when it was discovered that with antidromic signals from a motor neuron running collaterally back via the ventral root into the spinal cord there were interneurons firing with a high frequency resulting in inhibition Later work by Eccles et al 14 provided evidence that these interneurons which they called Renshaw Cells are stimulated by acetylcholine from motor neurons nicotinic receptor Previous work by Renshaw 15 and Lloyd 16 17 had shown that this antidromic inhibition resembled direct inhibition from spinal nerves but resulted in relatively longer inhibition of 40 50 ms compared to 15 ms The antidromic stimulation of the nerve fiber also resulted in action potentials in the cell bodies of the motor neurons along with hyperpolarization of other groups of motor neurons In the event where the initial stimulation of the motor neuron originated in a spinal tract the Renshaw cell spike occurred during the declining phase of the initial motor neuron soma spike giving an indication of the source and sequence of stimulation of the Renshaw cell References Edit George Z Mentis Valerie C Siembab Ricardo Zerda Michael J O Donovan and Francisco J Alvarez Primary Afferent Synapses on Developing and Adult Renshaw Cells The J of Neuroscience 2006 26 51 13297 13310 Mazzocchio R Rossi A Rothwell JC Depression of Renshaw recurrent inhibition by activation of corticospinal fibres in human upper and lower limb J Physiol Lond 1994 481 487 9 H Hultborn E Pierrot Deseilligny Changes in recurrent inhibition during voluntary soleus contractions in man studied by an H Reflex Technique J Phyeiol 1979 297 pp 229 251 Iles JF Pardoe J Changes in transmission in the pathway of heteronymous spinal recurrent inhibition from soleus to quadriceps motor neurons during movement in man Brain 1999 122 1757 64 Nielsen J Pierrot Deseilligny E Evidence of facilitation of soleus coupled Renshaw cells during voluntary co contraction of antagonistic ankle muscles in man J Physiol Lond 1996 493 603 11 Wilson VJ Talbot WH Kato M Inhibitory convergence upon Renshaw cells Journal of neurophysiology 1964 27 1063 1079 R W Ryall M F Piercey and C Polosa Intersegmental and intrasegmental distribution of mutual inhibition of Renshaw cells J Neurophysiol 34 700 1971 RYALL R W Renshaw cell mediated inhibition of Renshaw cells patterns of excitation and inhibition from impulses in motor axon collaterals J Neurophysiol 1970 33 257 270 R Granit J Haase and L T Rutledge Recurrent inhibition in relation to frequency of firing and limitation of discharge rate of extensor motoneurones J Physiol 1960 December 154 2 308 328 J Haase J van der Meulen Effects of supraspinal stimulation on Renshaw cells belonging to extensor motoneurones Journal of neurophysiology 10 1961 24 510 20 D R Curtis C J Game D Lodge and R M McCulloch A pharmacological study of Renshaw cell inhibition J Physiol 1976 June 258 1 227 242 Victor J Wilson amp William H Talbot Integration at an Inhibitory Interneurone Inhibition of Renshaw Cells Nature 1963 200 1325 1327 Renshaw B Central effects of centripetal impulses in axons of spinal ventral roots J Neurophysiol 1946 9 191 204 Eccles JC Fatt P Koketsu K Cholinergic and inhibitory synapses in a pathway from motor axon collaterals to motoneurones J Physiol 1954 126 524 562 Renshaw B Influence of discharge of motoneurons upon excitation of neighboring motoneurons J Neurophysiol 1941 4 167 Lloyd D P C Facilitation and inhibition of spinal motoneurons J Neurophysiol 1946 9 421 Lloyd D P C After currents after potentials excitability and ventral root electrotonus in spinal motoneurons J gen Physiol 1951 35 289External links EditDiagram at pediatricneuro com NIF Search Renshaw Cell via the Neuroscience Information Framework Retrieved from https en wikipedia org w index php title Renshaw cell amp oldid 1004533453, wikipedia, wiki, book, books, library,
