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The Journal of Physiology Dec 19951. Velocity information is used in the performance of movement. This study evaluated the ability of peripheral receptors to signal velocity in human subjects. 2. The...
1. Velocity information is used in the performance of movement. This study evaluated the ability of peripheral receptors to signal velocity in human subjects. 2. The velocity sensitivity of human muscle spindle afferents from the extensor digitorum muscles and slowly adapting type II cutaneous mechanoreceptors on the dorsum of the hand was evaluated with recordings from the radial nerve during imposed flexion movements about the metacarpophalangeal joint. Twenty-degree movements at velocities ranging from 5 to 80 deg s-1 were used. 3. Three measures of dynamic response were calculated: the dynamic positional sensitivity (the relation between discharge rate and joint angle during the dynamic phase of movement), the dynamic index (the discharge rate just before ramp completion minus the rate 0.5 s later), and the incremental response (the discharge rate just before ramp completion minus the rate just before ramp onset). 4. Both muscle spindle afferents and slowly adapting type II cutaneous mechanoreceptors demonstrated significant velocity sensitivity. The magnitudes of the relations between dynamic response measures and velocity were similar in the two receptor types. 5. These findings are consistent with the view that both muscle spindle afferents and slowly adapting type II cutaneous mechanoreceptors provide reasonable velocity signals.
Topics: Adult; Afferent Pathways; Humans; Kinetics; Mechanoreceptors; Middle Aged; Movement; Muscle Spindles; Sensitivity and Specificity; Skin Physiological Phenomena
PubMed: 8847650
DOI: 10.1113/jphysiol.1995.sp021075 -
The Journal of Physiology Dec 19751. The objectives of the investigation were to identify the muscle spindle endings which respond to cooling of the relaxed muscle and to study their response to stretch....
1. The objectives of the investigation were to identify the muscle spindle endings which respond to cooling of the relaxed muscle and to study their response to stretch. 2. The discharge of single afferents from 162 de-efferented muscle spindles in the relaxed medial gastrocnemius muscle of the anaesthetized cat was studied in vivo during cooling of the muscle from 37 to 24 degrees C. Temperature measurements were made at the inner surface of the muscle, while cooling (never below 15 degrees C) was applied at the skin over the muscle. 3. The endings were classified as primary or secondary endings on the basis of their conduction velocity, the dividing line being set at 70 m/sec. A response to cooling was obtained only from endings with afferents conducting at velocities of 20-70 m/sec. These fifty-six endings (CR) represented 65% of the secondary endings studied; the remaining secondary endings (NCR) and the primary endings showed no activity during cooling of the relaxed muscle. 4. During maintained stretches of 4-12 mm, activity of the NCR and primary endings decreased when the muscle was cooled. Cooling affected the CR endings in the same way, but only if the muscle was stretched 6 mm or more. During a smaller maintained muscle stretch, cooling caused an increase in CR activity, superimposed on the response to stretch. 5. The response to a 10 mm stretch at velocities of 10-70 mm/sec was studied in twenty-six CR, eleven NCR and twenty-one primary endings. 6. The dynamic responses of CR endings were intermediate between those of the primary endings and NCR endings. For any velocity of stretch the mean dynamic index of the CR endings was significantly greater than that of the NCR endings but significantly less than that of the primary endings. 7. The mean static responses of the CR and primary endings, measured 0-5 sec after the end of ramp stretch, were the same and significantly greater than that of the NCR endings. 8. The results indicate that cooling of the relaxed mammalian muscle may be used to differentiate between primary endings and about two-thirds of the secondary endings. The remaining secondary endings can be recognized by their small dynamic and static response to stretch.
Topics: Action Potentials; Animals; Cats; Cold Temperature; Denervation; Electric Stimulation; Muscle Contraction; Muscle Spindles; Muscles; Neural Conduction; Neurons, Afferent; Neurons, Efferent
PubMed: 129561
DOI: 10.1113/jphysiol.1975.sp011193 -
Journal of Neurophysiology Sep 2018Reference frame transformations (RFTs) are crucial components of sensorimotor transformations in the brain. Stochasticity in RFTs has been suggested to add noise to the...
Reference frame transformations (RFTs) are crucial components of sensorimotor transformations in the brain. Stochasticity in RFTs has been suggested to add noise to the transformed signal due to variability in transformation parameter estimates (e.g., angle) as well as the stochastic nature of computations in spiking networks of neurons. Here, we varied the RFT angle together with the associated variability and evaluated the behavioral impact in a reaching task that required variability-dependent visual-proprioceptive multisensory integration. Crucially, reaches were performed with the head either straight or rolled 30° to either shoulder, and we also applied neck loads of 0 or 1.8 kg (left or right) in a 3 × 3 design, resulting in different combinations of estimated head roll angle magnitude and variance required in RFTs. A novel three-dimensional stochastic model of multisensory integration across reference frames was fitted to the data and captured our main behavioral findings: 1) neck load biased head angle estimation across all head roll orientations, resulting in systematic shifts in reach errors; 2) increased neck muscle tone led to increased reach variability due to signal-dependent noise; and 3) both head roll and neck load created larger angular errors in reaches to visual targets away from the body compared with reaches toward the body. These results show that noise in muscle spindles and stochasticity in general have a tangible effect on RFTs underlying reach planning. Since RFTs are omnipresent in the brain, our results could have implications for processes as diverse as motor control, decision making, posture/balance control, and perception. NEW & NOTEWORTHY We show that increasing neck muscle tone systematically biases reach movements. A novel three-dimensional multisensory integration across reference frames model captures the data well and provides evidence that the brain must have online knowledge of full-body geometry together with the associated variability to plan reach movements accurately.
Topics: Adult; Analysis of Variance; Brain; Head Movements; Humans; Male; Motor Activity; Muscle Spindles; Neck Muscles; Orientation; Posture; Proprioception; Psychomotor Performance; Space Perception; Young Adult
PubMed: 29742021
DOI: 10.1152/jn.00643.2017 -
The Journal of Physiology Apr 2019Acetylcholine receptors are aggregated in the central regions of intrafusal muscle fibres. Single unit muscle spindle afferent responses from isolated mouse extensor...
KEY POINTS
Acetylcholine receptors are aggregated in the central regions of intrafusal muscle fibres. Single unit muscle spindle afferent responses from isolated mouse extensor digitorum longus muscle were recorded in the absence of fusimotor input to ramp and hold stretches as well as to sinusoidal vibrations in the presence and absence of the acetylcholine receptor blockers d-tubocurarine and α-bungarotoxin. Proprioceptive afferent responses to both types of stretch were enhanced in the presence of either blocker. Blocking acetylcholine uptake and vesicular acetylcholine release by hemicholinium-3 also enhanced stretch-evoked responses. These results represent the first evidence that acetylcholine receptors negatively modulate muscle spindle responses to stretch. The data support the hypothesis that the sensory nerve terminal is able to release vesicles to fine-tune proprioceptive afferent sensitivity.
ABSTRACT
Muscle spindles are complex stretch-sensitive mechanoreceptors. They consist of specialized skeletal muscle fibres, called intrafusal fibres, which are innervated in the central (equatorial) region by afferent sensory axons and in both polar regions by efferent γ-motoneurons. Previously it was shown that acetylcholine receptors (AChR) are concentrated in the equatorial region at the contact site between the sensory neuron and the intrafusal muscle fibre. To address the function of these AChRs, single unit sensory afferents were recorded from an isolated mouse extensor digitorum longus muscle in the absence of γ-motoneuron activity. Specifically, we investigated the responses of individual sensory neurons to ramp-and-hold stretches and sinusoidal vibrations before and after the addition of the competitive and non-competitive AChR blockers d-tubocurarine and α-bungarotoxin, respectively. The presence of either drug did not affect the resting action potential discharge frequency. However, the action potential frequencies in response to stretch were increased. In particular, frequencies of the dynamic peak and dynamic index to ramp-and-hold stretches were significantly higher in the presence of either drug. Treatment of muscle spindle afferents with the high-affinity choline transporter antagonist hemicholinium-3 similarly increased muscle spindle afferent firing frequencies during stretch. Moreover, the firing rate during sinusoidal vibration stimuli at low amplitudes was higher in the presence of α-bungarotoxin compared to control spindles also indicating an increased sensitivity to stretch. Collectively these data suggest a modulation of the muscle spindle afferent response to stretch by AChRs in the central region of intrafusal fibres possibly fine-tuning muscle spindle sensitivity.
Topics: Action Potentials; Animals; Bungarotoxins; Hemicholinium 3; Male; Mechanotransduction, Cellular; Mice; Mice, Inbred C57BL; Muscle Fibers, Skeletal; Muscle Spindles; Protein Transport; Receptors, Cholinergic; Sensory Receptor Cells; Tubocurarine
PubMed: 30673133
DOI: 10.1113/JP277139 -
PLoS Computational Biology Sep 2017Muscle spindle proprioceptive receptors play a primary role in encoding the effects of external mechanical perturbations to the body. During externally-imposed stretches...
Muscle spindle proprioceptive receptors play a primary role in encoding the effects of external mechanical perturbations to the body. During externally-imposed stretches of passive, i.e. electrically-quiescent, muscles, the instantaneous firing rates (IFRs) of muscle spindles are associated with characteristics of stretch such as length and velocity. However, even in passive muscle, there are history-dependent transients of muscle spindle firing that are not uniquely related to muscle length and velocity, nor reproduced by current muscle spindle models. These include acceleration-dependent initial bursts, increased dynamic response to stretch velocity if a muscle has been isometric, and rate relaxation, i.e., a decrease in tonic IFR when a muscle is held at a constant length after being stretched. We collected muscle spindle spike trains across a variety of muscle stretch kinematic conditions, including systematic changes in peak length, velocity, and acceleration. We demonstrate that muscle spindle primary afferents in passive muscle fire in direct relationship to muscle force-related variables, rather than length-related variables. Linear combinations of whole muscle-tendon force and the first time derivative of force (dF/dt) predict the entire time course of transient IFRs in muscle spindle Ia afferents during stretch (i.e., lengthening) of passive muscle, including the initial burst, the dynamic response to lengthening, and rate relaxation following lengthening. Similar to acceleration scaling found previously in postural responses to perturbations, initial burst amplitude scaled equally well to initial stretch acceleration or dF/dt, though later transients were only described by dF/dt. The transient increase in dF/dt at the onset of lengthening reflects muscle short-range stiffness due to cross-bridge dynamics. Our work demonstrates a critical role of muscle cross-bridge dynamics in history-dependent muscle spindle IFRs in passive muscle lengthening conditions relevant to the detection and sensorimotor response to mechanical perturbations to the body, and to previously-described history-dependence in perception of limb position.
Topics: Action Potentials; Computer Simulation; Elastic Modulus; Humans; Mechanotransduction, Cellular; Models, Biological; Muscle Spindles; Muscle, Skeletal; Physical Stimulation; Reflex, Stretch; Stress, Mechanical
PubMed: 28945740
DOI: 10.1371/journal.pcbi.1005767 -
Journal of Neural Engineering Apr 2017One goal of neuromorphic engineering is to create 'realistic' robotic systems that interact with the physical world by adopting neuromechanical principles from biology....
OBJECTIVE
One goal of neuromorphic engineering is to create 'realistic' robotic systems that interact with the physical world by adopting neuromechanical principles from biology. Critical to this is the methodology to implement the spinal circuitry responsible for the behavior of afferented muscles. At its core, muscle afferentation is the closed-loop behavior arising from the interactions among populations of muscle spindle afferents, alpha and gamma motoneurons, and muscle fibers to enable useful behaviors.
APPROACH
We used programmable very- large-scale-circuit (VLSI) hardware to implement simple models of spiking neurons, skeletal muscles, muscle spindle proprioceptors, alpha-motoneuron recruitment, gamma motoneuron control of spindle sensitivity, and the monosynaptic circuitry connecting them. This multi-scale system of populations of spiking neurons emulated the physiological properties of a pair of antagonistic afferented mammalian muscles (each simulated by 1024 alpha- and gamma-motoneurones) acting on a joint via long tendons.
MAIN RESULTS
This integrated system was able to maintain a joint angle, and reproduced stretch reflex responses even when driving the nonlinear biomechanics of an actual cadaveric finger. Moreover, this system allowed us to explore numerous values and combinations of gamma-static and gamma-dynamic gains when driving a robotic finger, some of which replicated some human pathological conditions. Lastly, we explored the behavioral consequences of adopting three alternative models of isometric muscle force production. We found that the dynamic responses to rate-coded spike trains produce force ramps that can be very sensitive to tendon elasticity, especially at high force output.
SIGNIFICANCE
Our methodology produced, to our knowledge, the first example of an autonomous, multi-scale, neuromorphic, neuromechanical system capable of creating realistic reflex behavior in cadaveric fingers. This research platform allows us to explore the mechanisms behind healthy and pathological sensorimotor function in the physical world by building them from first principles, and it is a precursor to neuromorphic robotic systems.
Topics: Action Potentials; Afferent Pathways; Animals; Biomimetics; Computer Simulation; Humans; Models, Neurological; Motor Neurons; Muscle Contraction; Muscle Spindles; Muscle, Skeletal; Neuromuscular Junction; Robotics; Signal Processing, Computer-Assisted; Synaptic Transmission
PubMed: 28084217
DOI: 10.1088/1741-2552/aa593c -
Sensors (Basel, Switzerland) Nov 2022Shortage of labor and increased work of young people are causing problems in terms of care and welfare of a growing proportion of elderly people. This is a looming...
Shortage of labor and increased work of young people are causing problems in terms of care and welfare of a growing proportion of elderly people. This is a looming social problem because people of advanced ages are increasing. Necessary in the fields of care and welfare, pneumatic artificial muscles in actuators of robots are being examined. Pneumatic artificial muscles have a high output per unit of weight, and they are soft, similarly to human muscles. However, in previous research of robots using pneumatic artificial muscles, rigid sensors were often installed at joints and other locations due to the robots' structures. Therefore, we developed a smart actuator that integrates a bending sensor that functions as a human muscle spindle; it can be externally attached to the pneumatic artificial muscle. This paper reports a smart artificial muscle actuator that can sense contraction, which can be applied to developed self-monitoring and robot posture control.
Topics: Humans; Aged; Adolescent; Muscle Spindles; Muscle, Skeletal; Robotics; Equipment Design
PubMed: 36433570
DOI: 10.3390/s22228975 -
Experimental Physiology Jan 2024The goals of this review are to improve understanding of the aetiology of chronic muscle pain and identify new targets for treatments. Muscle pain is usually associated... (Review)
Review
The goals of this review are to improve understanding of the aetiology of chronic muscle pain and identify new targets for treatments. Muscle pain is usually associated with trigger points in syndromes such as fibromyalgia and myofascial syndrome, and with small spots associated with spontaneous electrical activity that seems to emanate from fibers inside muscle spindles in EMG studies. These observations, added to the reports that large-diameter primary afferents, such as those innervating muscle spindles, become hyperexcitable and develop spontaneous ectopic firing in conditions leading to neuropathic pain, suggest that changes in excitability of these afferents might make an important contribution to the development of pathological pain. Here, we review evidence that the muscle spindle afferents (MSAs) of the jaw-closing muscles become hyperexcitable in a model of chronic orofacial myalgia. In these afferents, as in other large-diameter primary afferents in dorsal root ganglia, firing emerges from fast membrane potential oscillations that are supported by a persistent sodium current (I ) mediated by Na channels containing the α-subunit Na 1.6. The current flowing through Na 1.6 channels increases when the extracellular Ca concentration decreases, and studies have shown that I -driven firing is increased by S100β, an astrocytic protein that chelates Ca when released in the extracellular space. We review evidence of how astrocytes, which are known to be activated in pain conditions, might, through their regulation of extracellular Ca , contribute to the generation of ectopic firing in MSAs. To explain how ectopic firing in MSAs might cause pain, we review evidence supporting the hypothesis that cross-talk between proprioceptive and nociceptive pathways might occur in the periphery, within the spindle capsule.
Topics: Humans; Muscle Spindles; Myalgia; Chronic Pain; Membrane Potentials; Neuralgia; Neurons, Afferent
PubMed: 38103003
DOI: 10.1113/EP090769 -
The Journal of Physiology Jul 19801. These experiments were based on the recent observation of Gladden (1976), that acetylcholine (ACh) when applied to the isolated cat muscle spindle caused contraction...
1. These experiments were based on the recent observation of Gladden (1976), that acetylcholine (ACh) when applied to the isolated cat muscle spindle caused contraction of the dynamic and the static nuclear bag fibres, and not of the nuclear chain fibres, and that the dynamic nuclear bag fibre had the lower threshold to ACh than the static nuclear bag fibre. Subsequently, suxamethonium (SCh) has been shown to have similar effects on the intrafusal muscle fibres (Gladden & McWilliam, 1977). 2. In these experiments, the response of cat soleus muscle spindle primary, secondary and 'intermediate' sensory endings to repetitive ramp stretches during continuous slow infusions of SCh were studied. The changes observed are interpreted on the basis of the known action of SCh on the intrafusal muscle fibres of the isolated spindle. 3. Primary sensory endings, with afferent axon conduction velocities above 80 m/sec, were activated during SCh infusion in three stages. In Phase I of excitation, a gradual facilitation of the discharge of the Ia endings was seen, without potentiation of the dynamic or length sensitivity to stretch. In Phase II of excitation, the dynamic sensitivity of the Ia endings increased very markedly. In Phase III of excitation, an increase in length sensitivity was superimposed on the already enhanced dynamic sensitivity. 4. Secondary sensory endings, with afferent axon conduction velocities below 60 m/sec, only experienced a gradual facilitation of their discharge during SCh infusion, similar to the Phase I effects of SCh on primary endings. 5. The majority of 'intermediate' sensory endings, with afferent axon conduction velocities between 60 and 80 m/sec, were activated by SCh either in the same way as primary endings, or in the same way as secondary endings. However, a significant number of these sensory endings behaved in a truly intermediate manner during SCh infusion (cf. Rack & Westbury, 1966), and may represent an intermediate form of spindle sensory ending. 6. The afferent axon conduction velocities of these truly intermediate sensory endings were restricted to the range 69-77 m/sec. All the 'intermediate' endings which were activated in a primary-like manner had afferent axons conducting at velocities greater than 74 m/sec. 'Intermediate' endings which were activated in a secondary-like manner had afferent axon conduction velocities below 72 m/sec. 7. The probable contribution of the static and dynamic nuclear bag fibres to the discharge of each type of spindle sensory ending is discussed.
Topics: Action Potentials; Animals; Cats; Muscle Contraction; Muscle Spindles; Muscles; Neurons, Afferent; Succinylcholine
PubMed: 6449590
DOI: 10.1113/jphysiol.1980.sp013326 -
Scientific Reports Aug 2017Emotions can evoke strong reactions that have profound influences, from gross changes in our internal environment to small fluctuations in facial muscles, and reveal our...
Emotions can evoke strong reactions that have profound influences, from gross changes in our internal environment to small fluctuations in facial muscles, and reveal our feelings overtly. Muscles contain proprioceptive afferents, informing us about our movements and regulating motor activities. Their firing reflects changes in muscle length, yet their sensitivity can be modified by the fusimotor system, as found in animals. In humans, the sensitivity of muscle afferents is modulated by cognitive processes, such as attention; however, it is unknown if emotional processes can modulate muscle feedback. Presently, we explored whether muscle afferent sensitivity adapts to the emotional situation. We recorded from single muscle afferents in the leg, using microneurography, and moved the ankle joint of participants, while they listened to evocative classical music to induce sad, neutral, or happy emotions, or sat passively (no music). We further monitored their physiological responses using skin conductance, heart rate, and electromyography measures. We found that muscle afferent firing was modified by the emotional context, especially for sad emotions, where the muscle spindle dynamic response increased. We suggest that this allows us to prime movements, where the emotional state prepares the body for consequent behaviour-appropriate reactions.
Topics: Adult; Ankle Joint; Electromyography; Emotions; Feedback; Female; Galvanic Skin Response; Healthy Volunteers; Heart Rate; Humans; Male; Movement; Muscle Spindles; Muscle, Skeletal; Music; Neurons, Afferent; Proprioception
PubMed: 28814736
DOI: 10.1038/s41598-017-08721-4