Function of Medullated Small-Nerve Fibers in Mammalian Ventral Roots: Efferent Muscle Spindle Innervation

Kuffler, Stephen W.; Hunt, Carlton C.; Quilliam, J. P.

doi:10.1152/jn.1951.14.1.29

Cited by 306 publications

(125 citation statements)

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“…The phasic sensitivity of the primary ending is somewhat similar to the 'phase advance' or 'velocity feedback' used to stop oscillation in some inanimate control systems, and is thought to be of similar importance in the reflex stabilization of muscle contraction (Merton, 1951;Pringle & Wilson, 1952;Lippold et at. 1958 (Leksell, 1945;Kuffler et al 1951;Whitteridge, 1959). The contrasting finding that the slope of the frequency-extension relation did not always increase with an increasing excitatory effect on the ending appears, however, to be of equal interest.…”

Section: Discussionmentioning

confidence: 99%

The response of de‐efferented muscle spindle endings in the cat's soleus to slow extension of the muscle

Harvey¹,

Matthews²

1961

The Journal of Physiology

111

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The relation between the frequency of discharge of a muscle spindle ending and the extension applied to the muscle has been studied under various conditions (Eldred, Granit & Merton, 1953;Granit, 1958;Granit & Homma, 1959a; Whitteridge, 1959;Eldred, Lindsley & Buchwald, 1960). There has not, however, been any comparison of the properties of the primary and of the secondary afferent endings of the muscle spindle in this respect; nor is it known whether Whitteridge's finding for spindles in eye muscles, that intrafusal fibre contraction may increase the sensitivity of an ending to stretch, also holds for either the primary or the secondary endings of spindles in limb muscles. These points have, therefore, been investigated in the present work. The frequency-extension relations were determined under dynamic conditions by recording the discharge of an ending while the muscle was slowly stretched at a constant velocity. The use of this method showed incidentally that for de-efferented spindles the response of primary endings to the phasic component of the stretch is much more marked than that of secondary endings. This confirms the findings of Cooper (1959) for spindles with an intact motor supply. METHODS Preparation. The experiments were performed on 23 cats. One was decerebrated and the rest were anaesthetized with pentobarbitone sodium (Nembutal; Abbott Laboratories) given intraperitoneally. The discharge of single afferents from muscle spindle endings lying in the right soleus muscle was recorded from thin dorsal root filaments. Soleus was completely isolated from the spinal cord by cutting the L 6, L 7, S 1 and S2 dorsal and ventral roots. The nerves to most other leg and hip muscles, including the lateral head of gastrocnemius, were cut.Myography and application of 8tretch. The right tibia was fixed rigidly by pins and the tension in soleus recorded from the cut Achilles tendon by an isometric myograph which could be moved so as to extend soleus. The movement was at constant velocity, variable from about 0 5 mm/sec to about 9 mm/sec, and was produced by a screw thread driven by a speed-controlled motor. The extension was monitored by means of a microswitch which * M.R.C. Scholar.

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Section: Discussionmentioning

confidence: 99%

The response of de‐efferented muscle spindle endings in the cat's soleus to slow extension of the muscle

Harvey¹,

Matthews²

1961

The Journal of Physiology

111

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“…Indeed, in certain muscles it can be shown that a motor axon divides to innervate quite separate parts of the muscle. For example, in tenuissimus a motor axon may innervate muscle fibres which may be many centimetres apart (Adrian, 1925;Kuffler et al 1951).…”

Section: Skeletal Muscle Innervation Discussionmentioning

confidence: 99%

Motor innervation of skeletal muscle: multiple innervation of individual muscle fibres and motor unit function*

Hunt¹,

Kuffler²

1954

The Journal of Physiology

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“…Alpha motor neurons predominate within motor pools and innervate force-generating extrafusal muscle fibers at neuromuscular junctions (13). Gamma motor neurons constitute approximately one third of all motor neurons within a pool and innervate the intrafusal muscle fibers found in muscle spindles, where they modulate the sensitivity of muscle spindles to stretch (13)(14)(15)(16). Gamma and alpha motor neurons also differ profoundly with respect to their soma size and connectivity profile within the spinal cord.…”

mentioning

confidence: 99%

Gamma and alpha motor neurons distinguished by expression of transcription factor Err3

Friese

Kaltschmidt

Ladle

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

191

256

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Spinal motor neurons are specified to innervate different muscle targets through combinatorial programs of transcription factor expression. Whether transcriptional programs also establish finer aspects of motor neuron subtype identity, notably the prominent functional distinction between alpha and gamma motor neurons, remains unclear. In this study, we identify DNA binding proteins with complementary expression profiles in alpha and gamma motor neurons, providing evidence for molecular distinctions in these two motor neuron subtypes. The transcription factor Err3 is expressed at high levels in gamma but not alpha motor neurons, whereas the neuronal DNA binding protein NeuN marks alpha but not gamma motor neurons. Signals from muscle spindles are needed to support the differentiation of Err3 on /NeuN off presumptive gamma motor neurons, whereas direct proprioceptive sensory input to a motor neuron pool is apparently dispensable. Together, these findings provide evidence that transcriptional programs define functionally distinct motor neuron subpopulations, even within anatomically defined motor pools.motor neuron ͉ spinal cord ͉ transcription factors N euronal diversity underlies many features of central nervous system (CNS) organization and function. Neurons located within different regions of the CNS typically exhibit distinct morphologies and patterns of connectivity that help to determine their physiological functions. Within a single region, neurons that serve closely related functions can be further subdivided, both anatomically and physiologically. The retina, for example, contains multiple subclasses of ganglion and amacrine neurons that are distinguishable by position, patterns of dendritic arborization, and their role in visual processing (1, 2). Similarly, the cerebral cortex contains many local circuit interneurons, each with specialized anatomy, circuitry, and physiology (3). Little is known, however, about how such fine distinctions in CNS neuronal subtype identity and connectivity are assigned.The spinal cord represents a region of the CNS where the diversity of neuronal subtypes has been shown to emerge as a consequence of the expression of intrinsic molecular determinants, acting in a hierarchical manner to assign subtype identities to a generic set of motor neurons (4, 5). The motor neurons that project to skeletal muscle targets can be subdivided into distinct columnar subgroups, each projecting to a different target domain-axial, body wall, and limb targets. The lateral motor column (LMC) neurons that project their axons to limb muscles can be further subdivided into divisional and pool subclasses that, together, specify the pattern of target muscle connectivity (4, 5). The sequential steps involved in controlling motor neuron subtype identities and target projections are programmed through the cell-type selectivity of transcription factor expression, notably members of the Hox, LIM, Nkx6, and ETS families (6-10). Thus combinatorial programs of transcription factor expression appear to provide...

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Function of Medullated Small-Nerve Fibers in Mammalian Ventral Roots: Efferent Muscle Spindle Innervation

Cited by 306 publications

References 0 publications

The response of de‐efferented muscle spindle endings in the cat's soleus to slow extension of the muscle

The response of de‐efferented muscle spindle endings in the cat's soleus to slow extension of the muscle

Motor innervation of skeletal muscle: multiple innervation of individual muscle fibres and motor unit function*

Gamma and alpha motor neurons distinguished by expression of transcription factor Err3

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