Spatial synaptic distribution of recurrent and group Ia inhibitory systems in cat spinal motoneurones

Burke, Robert E.; Fedina, L.; Lundberg, A.

doi:10.1113/jphysiol.1971.sp009434

Cited by 111 publications

(45 citation statements)

References 27 publications

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“…While synaptic connections from interneurons primarily are located on the soma of the motor neuron (Burke et al 1971), Ia monosynaptic connections project to both the soma and the proximal dendrites (Brown and Fyffe 1981). However, in our model all synaptic currents were injected into the soma compartment, as the dynamics of the implemented synaptic currents were all based on measurements from the soma (Finkel and Redman 1983;Stuart and Redman 1990).…”

Section: Methodsmentioning

confidence: 99%

The optimal neural strategy for a stable motor task requires a compromise between level of muscle cocontraction and synaptic gain of afferent feedback

Dideriksen

Negro

Farina

2015

Journal of Neurophysiology

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Dideriksen JL, Negro F, Farina D. The optimal neural strategy for a stable motor task requires a compromise between level of muscle cocontraction and synaptic gain of afferent feedback. J Neurophysiol 114: 1895-1911, 2015. First published July 22, 2015 doi:10.1152/jn.00247.2015.-Increasing joint stiffness by cocontraction of antagonist muscles and compensatory reflexes are neural strategies to minimize the impact of unexpected perturbations on movement. Combining these strategies, however, may compromise steadiness, as elements of the afferent input to motor pools innervating antagonist muscles are inherently negatively correlated. Consequently, a high afferent gain and active contractions of both muscles may imply negatively correlated neural drives to the muscles and thus an unstable limb position. This hypothesis was systematically explored with a novel computational model of the peripheral nervous system and the mechanics of one limb. Two populations of motor neurons received synaptic input from descending drive, spinal interneurons, and afferent feedback. Muscle force, simulated based on motor unit activity, determined limb movement that gave rise to afferent feedback from muscle spindles and Golgi tendon organs. The results indicated that optimal steadiness was achieved with low synaptic gain of the afferent feedback. High afferent gains during cocontraction implied increased levels of common drive in the motor neuron outputs, which were negatively correlated across the two populations, constraining instability of the limb. Increasing the force acting on the joint and the afferent gain both effectively minimized the impact of an external perturbation, and suboptimal adjustment of the afferent gain could be compensated by muscle cocontraction. These observations show that selection of the strategy for a given contraction implies a compromise between steadiness and effectiveness of compensations to perturbations. This indicates that a task-dependent selection of neural strategy for steadiness is necessary when acting in different environments.

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Section: Methodsmentioning

confidence: 99%

The optimal neural strategy for a stable motor task requires a compromise between level of muscle cocontraction and synaptic gain of afferent feedback

Dideriksen

Negro

Farina

2015

Journal of Neurophysiology

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“…Burke, Fedina & Lundberg, 1971). Effects of depolarization and of hyperpolarization of the motoneurones were also tested, but the majority of results are from non-polarized motoneurones with action or membrane potential > 50-60 mV.…”

Section: Methodsmentioning

confidence: 99%

Oligosynaptic excitation of motoneurones by impulses in group Ia muscle spindle afferents in the cat

Jankowska¹,

McCrea²,

Mackel³

1981

The Journal of Physiology

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SUMMARY1. Intracellular recording from hind-limb motoneurones was used to investigate whether di-and trisynaptic (oligosynaptic) excitatory post-synaptic potentials (e.p.s.p.s) are evoked from group Ia muscle spindle afferents in those motoneurones in which such potentials are evoked from I b tendon organ afferents or entire group I afferents. I.a afferents of triceps surae and plantaris were activated either selectively by single brief stretches of these muscles, or together with Ib afferents by electrical stimuli applied to the nerves.2. Muscle stretches below threshold for lb afferents (10-35,um) evoked e.p.s.p.s which appeared with latencies compatible with disynaptic and trisynaptic coupling between the afferents and the motoneurones. The latencies of a majority of these e.p.s.p.s were too short to allow their mediation by group II afferents, if any were activated by the applied stretches. They were also too short to be compatible with effects attributable to dorsal root reflexes. These e.p.s.p.s are thus attributed to oligosynaptic actions of Ia afferents.3. Stretch-evoked di-and trisynaptic I a e.p.s.p.s were found in 83 % of motoneurones in which e.p.s.p.s were evoked by stimuli which activated both Ia and lb afferents; in five motoneurone species they were found in more than 90 %. These observations lead to the conclusion that group I a muscle spindle afferents evoke not only inhibitory but also excitatory actions in parallel with group lb tendon organ afferents.4. The distribution of Ia oligosynaptic stretch-evoked excitation from ankle and toe extensor muscles was compared with the distribution of Ia non-reciprocal inhibition as described by Jankowska, McCrea & Mackel (1981b). Excitation predominated in posterior biceps-semitendinosus motoneurones and inhibition in other species of motoneurones investigated, except those of intrinsic foot muscles (tibial motoneurones); similar proportions of the latter showed excitation and inhibition.

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“…In addition to motoneurones, some I a interneurones should terminate on ventral spinocerebellar tract neurones (Gustafsson & Lindstr6m, 1970) and on other Ia inhibitory interneurones (H. Hultborn & M. Santini, personal communication). The terminations on motoneurones would be mainly on the soma and the proximal parts of the dendrites (Burke, Fedina & Lundberg, 1971;Jankowska & Roberts, 1972 b), though possibly more distally on some kinds of motoneurones (unpublished observation). A few terminal axon collaterals of slightly different length would be likely to terminate on a single motoneurone (Jankowska & Roberts, 1972b).…”

Section: Morphology Of Ia Inhibitory Interneurones 817mentioning

confidence: 99%

Morphology of interneurones mediating Ia reciprocal inhibition of motoneurones in the spinal cord of the cat

Jankowska¹,

Lindström²

1972

The Journal of Physiology

232

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1. Interneurones identified by physiological criteria (Hultborn, Jankowska & Lindström, 1971b) to mediate Ia reciprocal inhibition of motoneurones in the spinal cord of the cat were stained by intracellular injection of a fluorescent dye (Procion Yellow). 2. The somas of the stained cells were found in Rexed's lamina VII, just dorsal or dorsomedial to the motor nuclei. Their size was about 30 × 20 μm. The cells had four to five slender, weakly branching dendrites. The total extension of their dendritic trees was about 600 μm dorsoventrally, 400 μm mediolaterally and 300 μm rostrocaudally. 3. The axons originated from a separate axon hillock or from the base of a dendrite. They were myelinated with external diameter of about 6–14 μm and projected to either the ipsilateral ventral or lateral funiculi. Early collaterals were found only exceptionally. Some axons bifurcated into an ascending and a descending branch within the funiculi. 4. The possibility of identifying the Ia inhibitory interneurones on purely morphological grounds is discussed.

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Spatial synaptic distribution of recurrent and group Ia inhibitory systems in cat spinal motoneurones

Cited by 111 publications

References 27 publications

The optimal neural strategy for a stable motor task requires a compromise between level of muscle cocontraction and synaptic gain of afferent feedback

The optimal neural strategy for a stable motor task requires a compromise between level of muscle cocontraction and synaptic gain of afferent feedback

Oligosynaptic excitation of motoneurones by impulses in group Ia muscle spindle afferents in the cat

Morphology of interneurones mediating Ia reciprocal inhibition of motoneurones in the spinal cord of the cat

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