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The Journal of Physiology Mar 19901. The two types of fusimotor neurones, dynamic and static, can be differentiated by their effects on muscle spindle afferents. We have recorded the activity of muscle...
1. The two types of fusimotor neurones, dynamic and static, can be differentiated by their effects on muscle spindle afferents. We have recorded the activity of muscle spindle primary afferents from the intercostal nerves of anaesthetized or decerebrate cats. A 4 Hz sinusoidal stretch was applied to the muscle containing the spindles of interest before and after crushing the nerve proximal to the recording site to eliminate fusimotor effects. The relative activity of the dynamic and static fusimotor neurones was inferred from the change in the spindle afferents' response. 2. Some areas of intercostal muscle normally showed phasic activity linked to respiration, where as other areas of intercostal muscle showed no EMG activity under our experimental conditions. In areas of intercostal muscle lacking EMG activity, the afferents' mean rate was higher and the modulation around the mean was lower at all phases of the breathing cycle when the efferent supply was intact. This result suggests the muscle spindles were receiving a steady level of static fusimotor activity. 3. Spindle primary afferents from regions of intercostal muscle that were typically recruited during respiration had an additional increase in mean rate and modulation around the mean rate in phase with the EMG activity. This is suggestive of phasic activation of dynamic fusimotor neurones in addition to static fusimotor discharge. 4. Thus, the two types of fusimotor neurones can be activated separately by the CNS to control the sensitivity of muscle spindles. The regional differences in the recruitment patterns of fusimotor neurones parallels the functional specializations of different areas of the intercostal muscles. The temporal modifications of fusimotor activity during each respiratory cycle means that the segmental reflex gain will vary in those intercostal muscles that are active during respiration. 5. These findings regarding the CNS recruitment of the two types of fusimotor neurones during respiration are similar to those reported for the hindlimb extensors during locomotion, but differ from those reported for jaw muscles during chewing. This may reflect differing control strategies being used by the CNS to meet the unique demands of the various rhythmical movements.
Topics: Action Potentials; Animals; Cats; Central Nervous System; Female; Male; Motor Neurons; Motor Neurons, Gamma; Muscle Spindles; Neurons, Afferent; Respiration; Time Factors
PubMed: 2141077
DOI: 10.1113/jphysiol.1990.sp017982 -
The Journal of Experimental Biology Jan 2023Animals move across a wide range of surface conditions in real-world environments to acquire resources and avoid predation. To effectively navigate a variety of...
Animals move across a wide range of surface conditions in real-world environments to acquire resources and avoid predation. To effectively navigate a variety of surfaces, animals rely on several mechanisms including intrinsic mechanical responses, spinal-level central pattern generators, and neural commands that require sensory feedback. Muscle spindle Ia afferents play a critical role in providing sensory feedback and informing motor control strategies across legged vertebrate locomotion, which is apparent in cases where this sensory input is compromised. Here, we tested the hypothesis that spindle Ia afferents from hindlimb muscles are important for coordinating forelimb landing behavior in the cane toad. We performed bilateral sciatic nerve reinnervations to ablate the stretch reflex from distal hindlimb muscles while allowing for motor neuron recovery. We found that toads significantly delayed the onset and reduced the activation duration of their elbow extensor muscle following spindle Ia afferent ablation in the hindlimbs. However, reinnervated toads achieved similar elbow extension at touchdown to that of their pre-surgery state. Our results suggest that while toads likely tuned the activation timing of forelimb muscles in response to losing Ia afferent sensation from the hindlimbs they were likely able to employ compensatory strategies that allowed them to continue landing effectively with reduced sensory information during take-off. These findings indicate muscle spindle Ia afferents may contribute to tuning complex movements involving multiple limbs.
Topics: Animals; Muscle Spindles; Lower Extremity; Forelimb; Hindlimb; Bufo marinus
PubMed: 36576050
DOI: 10.1242/jeb.244629 -
The Journal of Neuroscience : the... May 2019Proprioceptive feedback from Group Ia/II muscle spindle afferents and Group Ib Golgi tendon afferents is critical for the normal execution of most motor tasks, yet how...
Proprioceptive feedback from Group Ia/II muscle spindle afferents and Group Ib Golgi tendon afferents is critical for the normal execution of most motor tasks, yet how these distinct proprioceptor subtypes emerge during development remains poorly understood. Using molecular genetic approaches in mice of either sex, we identified 24 transcripts that have not previously been associated with a proprioceptor identity. Combinatorial expression analyses of these markers reveal at least three molecularly distinct proprioceptor subtypes. In addition, we find that 12 of these transcripts are expressed well after proprioceptors innervate their respective sensory receptors, and expression of three of these markers, including the heart development molecule , is significantly reduced in mice that lack muscle spindles. These data reveal as a putative marker for proprioceptive muscle spindle afferents. Moreover, they suggest that the phenotypic specialization of functionally distinct proprioceptor subtypes depends, in part, on extrinsic sensory receptor organ-derived signals. Sensory feedback from muscle spindle (MS) and Golgi tendon organ (GTO) sensory end organs is critical for normal motor control, but how distinct MS and GTO afferent sensory neurons emerge during development remains poorly understood. Using (bulk) transcriptome analysis of genetically identified proprioceptors, this work reveals molecular markers for distinct proprioceptor subsets, including some that appear selectively expressed in MS afferents. Detailed analysis of the expression of these transcripts provides evidence that MS/GTO afferent subtype phenotypes may, at least in part, emerge through extrinsic, sensory end organ-derived signals.
Topics: Animals; Feedback, Sensory; Female; Male; Mechanoreceptors; Membrane Proteins; Mice; Muscle Spindles; Phenotype; Proprioception
PubMed: 30926747
DOI: 10.1523/JNEUROSCI.2671-18.2019 -
Journal of Neurophysiology Jun 19901. One hundred and twenty-four muscle afferents from the finger extensor muscles were recorded from the radial nerve in human subjects. 2. The afferents were...
1. One hundred and twenty-four muscle afferents from the finger extensor muscles were recorded from the radial nerve in human subjects. 2. The afferents were provisionally classified as muscle spindle primary (78/124) and secondary afferents (25/124), and Golgi tendon organ afferents (21/124), on the basis of their response to 1) maximal twitch contractions, 2) 20- and 50-Hz sinusoids superimposed on ramp-and-hold stretches, 3) stretch sensitization, and 4) isometric contractions and sudden relaxations. 3. Ramp-and-hold stretches at two velocities, 10 and 50 degrees/s, were applied to the appropriate metacarpophalangeal (MCP) joint while the parent muscle remained relaxed. For each unit three discrete parameters were assessed: the presence or absence of 1) an initial burst at the commencement of the ramp stretch, 2) a deceleration response at the beginning of the hold phase, and 3) a prompt silencing at muscle shortening. In addition, two kinds of dynamic indexes were calculated for 79 of the muscle spindle afferents. 4. Most spindle afferents responded readily to stretch, whereas the Golgi tendon organ afferents produced very poor stretch responses. All of them lacked a static response, whereas the dynamic response, when present at all, consisted of only a few impulses. 5. The dynamic index was higher for spindle primaries than for secondaries, and this difference was statistically significant although the distribution was unimodal for spindle afferents as a group. Hence, this parameter was a poor discriminator. 6. Initial bursts, deceleration responses, and silences during imposed shortening were more common in spindle primaries than in secondaries. The differences were significant in all these respects. 7. The three discrete parameters were statistically pairwise independent for the spindle afferents, justifying the combination of the three into a useful battery for discrimination between primary and secondary spindle afferents and the use of this battery as a partial data base for a probability approach towards a solid classification of human muscle afferents.
Topics: Adolescent; Adult; Aged; Electrophysiology; Female; Humans; Isometric Contraction; Male; Mechanoreceptors; Middle Aged; Muscle Spindles; Neurons, Afferent; Physical Stimulation
PubMed: 2141632
DOI: 10.1152/jn.1990.63.6.1297 -
Swedish Dental Journal 1987Jaw muscle motor behaviour, however complicated, has important implications for the every day dental practice. In recent years the understanding of jaw and other... (Review)
Review
Jaw muscle motor behaviour, however complicated, has important implications for the every day dental practice. In recent years the understanding of jaw and other skeletal muscle function has increased considerably. Direct recording of primary afferent discharge in conscious human beings and animals during normal function has caused radical changes of the concepts of muscle receptor function. Central pattern generators at segmental levels and suprasegmental programming centres are important mechanisms behind voluntary and automatic movements of different kinds. The most important proprioceptive function is probably to provide reassurance of correct movement pattern, to adjust the central programming to environmental changes and to directly influence slow movements requiring precision. Muscle spindle receptors contribute to mandibular kinesthesia. Muscle spindles are rarely present in jaw opening muscles. Despite this fact an excitatory reflex similar to the stretch reflex but with longer latency has been demonstrated. Further on a reciprocal organisation with antagonist inhibition has been shown to exist between jaw openers and closers. Motor behaviour of jaw and limb muscles thus seem to have many characteristics in common.
Topics: Humans; Masticatory Muscles; Motor Neurons; Movement; Muscle Spindles; Proprioception
PubMed: 2964735
DOI: No ID Found -
Journal of Electron Microscopy 1997We examined a muscle spindle in the posterior cricoarytenoid muscle of the adult guinea pig. The spindle capsule contained three intrafusal muscle fibres. At the...
We examined a muscle spindle in the posterior cricoarytenoid muscle of the adult guinea pig. The spindle capsule contained three intrafusal muscle fibres. At the equatorial region, three intrafusal fibres did not form a typical aggregation of nuclei such as bags and chains observed in common mammalian muscle spindles. Two intrafusal fibres of the three were innervated by sensory endings which branched and arranged irregularly. These sensory endings lay on the surface of intrafusal fibres in shallow grooves or deeply penetrated into the fibre. The third intrafusal fibre, lacking sensory innervation, showed a similar fine structure to extrafusal fibres. These findings suggest that the muscle spindle in the posterior cricoarytenoid muscle of the guinea pig is strikingly different in the structure of intrafusal fibres and in the arrangement of sensory endings from that in common mammalian skeletal muscles. The occurrence and role of these different structures were discussed.
Topics: Animals; Guinea Pigs; Larynx; Microscopy, Electron; Muscle Fibers, Skeletal; Muscle Spindles; Muscle, Skeletal
PubMed: 9279020
DOI: 10.1093/oxfordjournals.jmicro.a023518 -
Journal of Electromyography and... Dec 2018The objective of this study was to establish neural interactions between transspinal evoked potentials (TEPs) and muscle spindle group Ia afferents in healthy humans....
The objective of this study was to establish neural interactions between transspinal evoked potentials (TEPs) and muscle spindle group Ia afferents in healthy humans. Soleus H-reflexes were assessed following transspinal stimulation at conditioning-test (C-T) intervals that ranged from negative to positive 100 ms. TEPs were recorded from the right and left ankle/knee flexor and extensor muscles, and their amplitude was assessed following stimulation of soleus muscle spindle group Ia afferents at similar C-T intervals. Transspinal conditioning stimulation produced a short-latency, long-lasting soleus H-reflex depression. Excitation of muscle spindle group Ia afferents produced depression of ipsilateral ankle TEPs and medium-latency facilitation of the ipsilateral knee TEPs. At specific C-T intervals, the soleus H-reflex and ipsilateral ankle TEPs were summated based on their relative onset and duration. No changes were observed in the contralateral TEPs. These effects were exerted at both peripheral and spinal levels. Both transspinal and muscle spindle group Ia afferent stimulation produce long-lasting depression of the soleus H-reflex and TEPs, respectively. Transspinal stimulation may promote targeted neuromodulation and can be utilized in upper motoneuron lesions to normalize spinal reflex hyper-excitability and alter excitation thresholds of peripheral nerve axons.
Topics: Adult; Afferent Pathways; Evoked Potentials, Motor; H-Reflex; Humans; Male; Muscle Spindles; Muscle, Skeletal
PubMed: 30352388
DOI: 10.1016/j.jelekin.2018.10.005 -
Brain : a Journal of Neurology Nov 2011The Riley-Day syndrome is the most common of the hereditary sensory and autonomic neuropathies (Type III). Among the well-recognized clinical features are reduced pain...
The Riley-Day syndrome is the most common of the hereditary sensory and autonomic neuropathies (Type III). Among the well-recognized clinical features are reduced pain and temperature sensation, absent deep tendon reflexes and a progressively ataxic gait. To explain the latter we tested the hypothesis that muscle spindles, or their afferents, are absent in hereditary sensory and autonomic neuropathy III by attempting to record from muscle spindle afferents from a nerve supplying the leg in 10 patients. For comparison we also recorded muscle spindles from 15 healthy subjects and from two patients with hereditary sensory and autonomic neuropathy IV, who have profound sensory disturbances but no ataxia. Tungsten microelectrodes were inserted percutaneously into fascicles of the common peroneal nerve at the fibular head. Intraneural stimulation within muscle fascicles evoked twitches at normal stimulus currents (10-30 µA), and deep pain (which often referred) at high intensities (1 mA). Microneurographic recordings from muscle fascicles revealed a complete absence of spontaneously active muscle spindles in patients with hereditary sensory and autonomic neuropathy III; moreover, responses to passive muscle stretch could not be observed. Conversely, muscle spindles appeared normal in patients with hereditary sensory and autonomic neuropathy IV, with mean firing rates of spontaneously active endings being similar to those recorded from healthy controls. Intraneural stimulation within cutaneous fascicles evoked paraesthesiae in the fascicular innervation territory at normal stimulus intensities, but cutaneous pain was never reported during high-intensity stimulation in any of the patients. Microneurographic recordings from cutaneous fascicles revealed the presence of normal large-diameter cutaneous mechanoreceptors in hereditary sensory and autonomic neuropathy III. Our results suggest that the complete absence of functional muscle spindles in these patients explains their loss of deep tendon reflexes. Moreover, we suggest that their ataxic gait is sensory in origin, due to the loss of functional muscle spindles and hence a compromised sensorimotor control of locomotion.
Topics: Adolescent; Adult; Dysautonomia, Familial; Electric Stimulation; Female; Gait Ataxia; Humans; Male; Middle Aged; Motor Neurons; Muscle Spindles; Neural Conduction; Peroneal Nerve
PubMed: 22075519
DOI: 10.1093/brain/awr168 -
Computational Intelligence and... 2010Afferent muscle spindle activity in response to passive muscle stretch was recorded in vivo using thin-film longitudinal intrafascicular electrodes. A neural spike...
Afferent muscle spindle activity in response to passive muscle stretch was recorded in vivo using thin-film longitudinal intrafascicular electrodes. A neural spike detection and classification scheme was developed for the purpose of separating activity of primary and secondary muscle spindle afferents. The algorithm is based on the multiscale continuous wavelet transform using complex wavelets. The detection scheme outperforms the commonly used threshold detection, especially with recordings having low signal-to-noise ratio. Results of classification of units indicate that the developed classifier is able to isolate activity having linear relationship with muscle length, which is a step towards online model-based estimation of muscle length that can be used in a closed-loop functional electrical stimulation system with natural sensory feedback.
Topics: Action Potentials; Algorithms; Animals; Electrodes; Linear Models; Models, Biological; Muscle Spindles; Muscle, Skeletal; Neurons, Afferent; ROC Curve; Rabbits; Signal Processing, Computer-Assisted; Time Factors
PubMed: 20369071
DOI: 10.1155/2010/836346 -
Biological Cybernetics Oct 1996We address the issue of what proprioceptive information, regarding movement of the human arm, may be provided to the central nervous system by proprioceptors located...
We address the issue of what proprioceptive information, regarding movement of the human arm, may be provided to the central nervous system by proprioceptors located within muscles of this limb. To accomplish this we developed a numerical simulation which could provide estimates of the length regimes experienced by a set of model receptors located within some of the principal muscles of the human arm during planar movement of this limb. These receptors were assumed to have characteristics analogous to those associated with a simple model of muscle spindle signalling of movement. To this end each spindle had proprioceptive 'channels' associated with it. These corresponded to primary and secondary spindle afferent fibers which could provide independent afferent output regarding the parent muscle the spindle monitored. The angles of the shoulder and elbow joints attained by subjects performing a task requiring movement of the right arm in a horizontal plane to a static visual target were recorded. For this angular data the lengths and rates of change of lengths experienced by muscle fascicles, and hence the model spindles, during movement were calculated by means of the numerical simulation. The discharge rates of the simulated spindles during the movement were calculated to derive a measure of the depth of modulation, induced by the movement, for each spindle. These values were then summed for all spindles to provide a first-order approximation of spindle ensemble coding of the movement. Significant correlations (P < 0.0001, Spearman's rank order) were found between the resulting ensemble encodings and, in order of significance, the angular velocity of the shoulder joint (rS = 0.945), the tangential velocity of the hand (rS = 0.942), and the angular velocity of the elbow joint (rS = 0.917). Correlations between the angular positions of the shoulder (rS = -0.623) and elbow (rS = 0.628) were lower. These findings indicate that the ensemble profiles of the simulated muscle spindles, encode information regarding kinematic parameters of movements related to both intrinsic and extrinsic coordinate systems. This suggests that motor structures capable of deriving such an ensemble encoding would be in a position to perform the sensory-motor transformations between intrinsic and extrinsic frames of reference necessary for controlling movements planned in extrinsic coordinates.
Topics: Arm; Computer Simulation; Humans; Kinesthesis; Models, Theoretical; Movement; Muscle Spindles
PubMed: 8953743
DOI: 10.1007/s004220050300