Tendon Organs Research Articles

Stabilizing PID Controllers for a Single-Link Biomechanical Model with Position, Velocity, and Force Feedback

In this paper we address the problem of PID stabilization of a single-link inverted pendulum-based biomechanical model with force feedback, two levels of position and velocity feedback, and with delays in all the feedback loops. The novelty of the proposed model lies in its physiological relevance, whereby both small and medium latency sensory feedbacks from muscle spindle (MS), and force feedback from Golgi tendon organ (GTO) are included in the formulation. The biomechanical model also includes active and passive viscoelastic feedback from Hill-type muscle model and a second-order low-pass function for muscle activation. The central nervous system (CNS) regulation of postural movement is represented by a proportional-integral-derivative (PID) controller. Padé approximation of delay terms is employed to arrive at an overall rational transfer function of the biomechanical model. The Hermite-Biehler theorem is then used to derive stability results, leading to the existence of stabilizing PID controllers. An algorithm for selection of stabilizing feedback gains is developed using the linear matrix inequality (LMI) approach.

Perception of non-voluntary brief contractions in normal subjects and in a deafferented patient

The accuracy of force perception by human subjects in the absence of voluntary motor command was evaluated by exploring how they perceived isometric twitches of wrist extensor muscles produced by external stimulation. Twelve normal subjects and a well-known patient lacking large-diameter afferent fibres (GL) performed estimation, production and reproduction tasks. Magnetic stimulation of the radial nerve and, in normal subjects, transcranial magnetic stimulation (TMS) of the motor cortex were used to produce weak brief non-voluntary twitches. In estimation tasks, the subjects had to ascribe verbal marks on a 1-5 scale to the forces of stimulation-induced twitches. Loose covariations of marks and forces were observed, while directions of force variations between successive twitches were relatively well detected. GL did less well than normal subjects in detecting directions of force variations. In production tasks, subjects had to produce twitches matching verbal command marks in a 1-5 range, with or without visual feedback. Performances of normal subjects and GL resembled those of estimation tasks and were not improved by visual feedback. In reproduction tasks, subjects had to duplicate stimulation-induced test twitches: first without visual feedback, second with and third again without. Large errors were observed but all subjects did better with visual feedback. In the third step, improvement with respect to the first one was significantly more marked with TMS than with peripheral stimulation. GL improved her performance in the third step, possibly because she could use information provided by group III and group IV afferents still present in her nerves. Altogether, for normal subjects (1) the performances in estimation tasks are consistent with the known behaviour of Golgi tendon organs as observed in animal experiments, and (2) results observed in reproduction tasks suggest that cortical stimulation might elicit, in addition to corticospinal activation of motoneurones, collateral discharges that could be stored as a memory of motor command.

Contribution of force feedback to ankle extensor activity in decerebrate walking cats.

Previous investigations have demonstrated that feedback from ankle extensor group Ib afferents, arising from force-sensitive Golgi tendon organs, contributes to ankle extensor activity during the stance phase of walking in the cat. The objective of this investigation was to gain insight into the magnitude of this contribution by determining the loop gain of the positive force feedback pathway. Loop gain is the relative contribution of force feedback to total muscle activity and force. In decerebrate cats, the isolated medial gastrocnemius muscle (MG) was held at different lengths during sequences of rhythmic contractions associated with walking in the other three legs. We found that MG muscle activity and force increased at longer muscle lengths. A number of observations indicated that this length dependence was not due to feedback from muscle spindles. In particular, activity in group Ia afferents was insensitive to changes in muscle length during the MG bursts, and electrical stimulation of group II afferents had no influence on the magnitude of burst activity in other ankle extensors. We concluded that the homonymous positive force feedback pathway was isolated from other afferent pathways, allowing the use of a simple model of the neuromuscular system to estimate the pathway loop gain. This gain ranged from 0.2 at short muscle lengths to 0.5 at longer muscle lengths, demonstrating that force feedback was of modest importance at short muscle lengths, accounting for 20% of total activity and force, and of substantial importance at long muscle lengths, accounting for 50%. This length dependence was due to the intrinsic force-length property of muscle. The gain of the pathway that converts muscle force to motoneuron depolarization was independent of length. We discuss the relevance of this conclusion to the generation of ankle extensor activity in intact walking cats. These findings emphasize the general importance of feedback in generating ankle extensor activity during walking in the cat.

Contribution of sensory feedback to ongoing ankle extensor activity during the stance phase of walking

Numerous investigations over the past 15 years have demonstrated that sensory feedback plays a critical role in establishing the timing and magnitude of muscle activity during walking. Here we review recent studies reporting that sensory feedback makes a substantial contribution to the activation of extensor motoneurons during the stance phase. Quantitative analysis of the effects of loading and unloading ankle extensor muscles during walking on a horizontal surface has shown that sensory feedback can increase the activity of ankle extensor muscles by up to 60%. There is currently some uncertainty about which sensory receptors are responsible for this enhancement of extensor activity, but likely candidates are the secondary spindle endings in the ankle extensors of humans and the Golgi tendon organs in the ankle extensors of humans and cats. Two important issues arise from the finding that sensory feedback from the leg regulates the magnitude of extensor activity. The first is the extent to which differences in the magnitude of activity in extensor muscles during different locomotor tasks can be directly attributed to changes in the magnitude of sensory signals, and the second is whether the enhancement of extensor activity is determined primarily by feedback from a specific group of receptors or from numerous groups of receptors distributed throughout the leg. Limitations of current experimental strategies prevent a straightforward empirical resolution of these issues. A potentially fruitful approach in the immediate future is to develop models of the known and hypothesized neuronal networks controlling motoneuronal activity, and use these simulations to control forward dynamic models of the musculo-skeletal system. These simulations would help understand how sensory signals are modified with a change in locomotor task and, in conjunction with physiological experiments, establish the extent to which these modifications can account for changes in the magnitude of motoneuronal activity.

Corticotropin-releasing factor 2 receptor localization in skeletal muscle.

Our objective in this study was to localize the corticotropin-releasing factor 2 receptor (CRF2R) in rodent and human skeletal muscle. We found CRF2R protein to be abundant in neural tissues in skeletal muscle, including large nerve fibers and bundles, neural tissue associated with mechanoreceptors, muscle spindles, and the Golgi tendon organ. CRF2R protein was also abundant in blood vessels in skeletal muscle. CRF2R protein was also observed, although with less abundance, in the endo/perimysial regions in skeletal muscle. The localization of the CRF2R to blood vessels is consistent with the CRF2R-mediated vascular phenomena observed previously, but the observation of CRF2R in neural tissue in skeletal muscle is a novel finding with an unknown function.

Quais são as funções dos mecanoreceptores da articulação do ombro?: uma revisão da literatura

Nontraumatic glenohumeral instability is the most common shoulder pathology among young people causing pain and impingement syndrome symptoms. This instability usually affects athletes who perform overhand activities such as throwing and swimming. The glenohumeral stability is usually provided by rotator cuff musculature and capsule-ligament structures (glenoid labrum, glenohumeral ligaments and capsule). In order to control the synergistic relationship between muscles and capsuloligamentous structures, the somatosensory system located in the glenohumeral joint plays an essential function. These mechanoreceptors, Pacini, Ruffini and Golgi tendon organs are functionally distributed in the shoulder joints, and they have a complex relationship with the shoulder's musculature. According to the latencies obtained between stimuli in shoulder joints and muscular responses, suggests the consideration that mechanoreceptors not only contribute to detection of movement direction and joint position sense, but are also implicated in the control of movements and coordination. Rehabilitation programs for altered movement patterns using proprioceptive techniques appear to be justifiable. Also, to enhance proprioceptive techniques, more attention should be focused on shoulder exercises that use sequences and coordination in their execution.

Stochastic resonance in muscle receptors.

Noise is generally considered to have deleterious effects on the sensitivity of a signal detection system. There are, however, several mechanisms whereby the addition of noise to the input of a system can in fact improve sensitivity. One such mechanism is stochastic resonance. Although first proposed in 1981, conclusive experimental evidence for "fully tuneable stochastic resonance" in biological systems has not previously been reported. Evidence of fully tuneable stochastic resonance in the response of afferents from Golgi tendon organs and the primary and secondary endings of muscle spindles to imposed muscle length changes is presented.

Morphological study of the Golgi tendon organ in equine superficial digital flexor tendon.

The Golgi tendon organ (GTO) is an encapsulated fusiform mechanoreceptor siding in the musculo-tendinous junction of many animal species. Inhibitory function of afferent nerve fibers distributed from nearby motor units, the organ responds to active tension exerted onto the muscle. The morphological features of the equine GTO have not yet been elucidated. Additionally, there is some controversy regarding to the existence of the GTO in the equine superficial digital flexor tendon (SDFT). Therefore, immunohistochemistry and immunoelectron microscopy using alcian blue (pH 2.5) staining and the silver-enhanced colloidal gold method were carried out to determine both the location and characteristics of the GTO at the musculo-tendinous junction of the SDFT. A GTO with a fusiform structure of approximately 3 mm in length was found in the tendinous part. The lumen of the GTO was divided into compartments by septal cells. Each compartment contained collagen fibrils, nerve fibers and Schwann cells. This is the first report of the equine GTO.

Positive force feedback in bouncing gaits?

During bouncing gaits (running, hopping, trotting), passive compliant structures (e.g. tendons, ligaments) store and release part of the stride energy. Here, active muscles must provide the required force to withstand the developing tendon strain and to compensate for the inevitable energy losses. This requires an appropriate control of muscle activation. In this study, for hopping, the potential involvement of afferent information from muscle receptors (muscle spindles, Golgi tendon organs) is investigated using a two-segment leg model with one extensor muscle. It is found that: (i) positive feedbacks of muscle-fibre length and muscle force can result in periodic bouncing; (ii) positive force feedback (F+) stabilizes bouncing patterns within a large range of stride energies (maximum hopping height of 16.3 cm, almost twofold higher than the length feedback); and (iii) when employing this reflex scheme, for moderate hopping heights (up to 8.8 cm), an overall elastic leg behaviour is predicted (hopping frequency of 1.4-3 Hz, leg stiffness of 9-27 kN m(-1)). Furthermore, F+ could stabilize running. It is suggested that, during the stance phase of bouncing tasks, the reflex-generated motor control based on feedbacks might be an efficient and reliable alternative to central motor commands.

Motor and sensory innervation of extraocular eye muscles.

Eye muscles are unusual in several ways; one is that they have up to three different layers-the inner global layer, the outer orbital layer, and in some species an external marginal layer has been described. In sheep this is called the "peripheral patch layer." Three different types of proprioceptors are found in eye muscles-muscle spindles, Golgi tendon organs, and palisade endings. A survey of the organization of their location leads us to the hypothesis that each receptor is confined to a separate layer of the eye muscle. The palisade endings are associated with the global layer, the muscle spindles lie predominantly in the orbital layer, and the Golgi tendon organs are found only in the peripheral patch layer. This well-organized scheme may help us to understand the proprioceptive system in eye muscles.

Muscle spindles and Golgi tendon organs in bovine calf extraocular muscle studied by means of double-fluorescent labeling, electron microscopy, and three-dimensional reconstruction

In the present study muscle spindles (MSps) and Golgi tendon organs (GTOs) in bovine extraocular muscles (EOMs) were analyzed in detail. The innervation pattern of these proprioceptors was investigated with transmission electron microscope and confocal laser scanning microscope after double-fluorescent labeling. Three-dimensional (3D) reconstructions were performed of GTOs. Muscle spindles. MSps are numerous, each containing two nuclear bag fibers and up to eight nuclear chain fibers. In the equatorial region and paraequatorial region thin axons enwrapping the intrafusal muscle fibers form numerous nerve contacts on the muscle fiber surface. Double staining of such nerve terminals with synaptophysin and α-bungarotoxin and their fine structural features confirm their sensory nature. In the encapsulated part of the polar region neuromuscular contacts have structural features of motor nerve terminals and stain positively with α-bungarotoxin. Golgi tendon organs. GTOs are numerous in bovine EOMs. Each GTO contains collagen bundles but frequently also intracapsular muscle fibers. Intracapsular muscle fibers either terminate inside the GTO in collagen bundles or pass through the proprioceptor. GTOs are richly supplied with sensory nerve terminals which intermingle with the collagen bundles. Nerve terminals on intracapsular muscle fibers exhibit fine structural characteristics of motor nerve terminals and are α-bungarotoxin positive. The 3D images of GTOs show the detailed spatial arrangement of the GTO tissue components. These new insights in the complex and specific morphology of MSps and GTOs in bovine EOMs indicate that we deal with highly developed proprioceptors. These are supposed to provide important information for EOM innervation.

Tendon organs as monitors of muscle damage from eccentric contractions.

Eccentric contractions, where the active muscle is stretched, can lead to muscle damage. One of the signs of damage is a rise in the whole-muscle passive tension. Here we have asked, how many eccentric contractions are necessary to produce a measurable rise in passive tension and can this be detected by the muscle's tension sensors, the tendon organs? Responses of tendon organs of the medial gastrocnemius muscle of the anaesthetised cat were recorded during and after a series of eccentric contractions. The contractions were arranged so that the length change to which the muscle was subjected lay symmetrically about the optimum length for active tension. Tendon organ responses were measured as a mean rate, calculated over a 1-mm length change during a slow stretch of the muscle. Progressive increases in passive tension and tendon organ response were measured after each of a series of 1-100 eccentric contractions of the whole muscle, bundles of motor units and single motor units. One to two eccentric contractions of a single motor unit were sufficient to produce measurable rises in passive tension and tendon organ response. After a series of eccentric contractions had been completed, passive tension and tendon organ response were seen to continue rising with similar time-courses over the next 50 min. Both tension and afferent response could be reduced by large passive stretches. There was also a large increase in the responses of tendon organs to combined stretch and vibration at 100 Hz after the eccentric contractions. All of this indicates that tendon organs are able to monitor the passive tension changes in the muscle, thought to result from muscle damage produced by the eccentric contractions. The findings are relevant to known changes in proprioception and motor control after eccentric exercise.

Neuregulins and the neuromuscular system: 10 years of answers and questions.

The neuregulins were originally discovered in searches for the acetylcholine receptor-inducing activity (ARIA), glial growth factor (GGF), and a ligand for the oncogene neu (ErbB2/HER2). Neuregulin1 (NRG1)-mediated cell communication is critical in the central and peripheral nervous system, heart, breast, and other organ systems. This review will focus on the functions of NRG1s in the development and maintenance of the neuromuscular system and on the regulation of NRG1 signaling within this system. The roles of NRG1 signaling in the neuromuscular system are far more pervasive than contemplated when neuregulins were discovered 10 years ago. In fact, neuregulin-mediated cell communication plays an essential role in the biology of most components of the neuromuscular system--including motor and sensory neurons, muscle fibers, Schwann cells, and major specializations (neuromuscular synapses, muscle spindles, Golgi tendon organs, and peripheral nerves). It is argued here that while NRG1 proteins are indeed "ARIA" and "GGF", their involvement in regulating synapse-specific transcription and Schwann cell development is more complex than originally proposed. It is also argued that NRG1 isoforms differ in their signaling properties and that these differences tailor specific isoforms for specific signaling tasks; for example, some NRG1 isoforms may be specialized for paracrine signaling and others for juxtacrine signaling. In the first 10 years of neuregulin research there has been much progress in understanding the actions of neuregulins in shaping and maintaining the neuromuscular system. However, major questions, old and new, remain unanswered; and the second 10 years promises to be at least as exciting as the first.

Golgi Recruitment of GRIP Domain Proteins by Arf-like GTPase 1 Is Regulated by Arf-like GTPase 3

Golgins are Golgi-localized proteins present in all molecularly characterized eukaryotes that function in Golgi transport and maintenance of Golgi structure. Some peripheral membrane Golgins, including the yeast Imh1 protein, contain the recently described GRIP domain that can independently mediate Golgi localization by an unknown mechanism [1–3]. To identify candidate Golgi receptors for GRIP domain proteins, a collection of Saccharomyces cerevisiae deletion mutants was visually screened by using yeast, mouse, and human GFP-GRIP domain fusion proteins for defects in Golgi localization. GFP-GRIP reporters were localized to the cytosol in cells lacking either of two ARF-like (ARL) GTPases, Arl1p and Arl3p. In vitro binding experiments demonstrated that activated Arl1p-GTP binds specifically and directly to the Imh1p GRIP domain. Arl1p colocalized with Imh1p-GRIP at the Golgi, and Golgi localization of Arl1p was regulated by the GTPase cycle of Arl3p. These results suggest a cascade in which the GTPase cycle of Arl3p regulates Golgi localization of Arl1p, which in turn binds to the GRIP domain of Imh1p and recruits it to the Golgi. The similar requirements for localization of GRIP domains from yeast, mouse, and human when expressed in yeast, and the presence of Arl1p and Arl3p homologs in these species, suggest that this is an evolutionarily conserved mechanism.

Modulatory Effects of α1-,α2-, and β-Receptor Agonists on Feline Spinal Interneurons with Monosynaptic Input from Group I Muscle Afferents

Previous studies have shown that monoamines may modulate operation of spinal neuronal networks by depressing or facilitating responses of the involved neurons. Recently, activation of interneurons mediating reciprocal inhibition from muscle spindle (Ia) afferents and nonreciprocal inhibition from muscle spindle and tendon organ (Ia/Ib) afferents in the cat was found to be facilitated by noradrenaline (NA). However, which subclass membrane receptors are involved in mediating this facilitation was not established; the aim of the present experiments was to investigate this. Individual Ia- and Ia/Ib-inhibitory interneurons were identified in the cat lumbar spinal cord, and NA agonists were applied close to these neurons by ionophoresis. The agonists included the alpha1-receptor agonist phenylephrine, the alpha2-receptor agonists clonidine and tizanidine, and the beta-receptor agonist isoproterenol. Effects were measured by comparing changes in the number of extracellularly recorded spike potentials evoked by electrical stimulation of muscle nerves and changes in the latency of these potentials before, during, and after application of the tested compounds. Results show that the facilitatory effect of phenylephrine is as strong as that of NA, whereas the facilitatory effect of isoproterenol is weaker. Clonidine depressed activity of both Ia- and Ia/Ib-inhibitory interneurons, whereas tizanidine had no effect. These findings lead to the conclusion that beneficial antispastic effects of clonidine and tizanidine in humans are unlikely to be associated with an enhancement of the actions of Ia- and Ia/Ib-inhibitory interneurons, and the findings also support previous proposals that these compounds exert their antispastic actions via effects on other neuronal populations.

Separation and estimation of muscle spindle and tension receptor populations by vibration of the biceps muscle in the frog.

Frog spinal cord reflex behaviors have been used to test the idea of spinal primitives. We have suggested a significant role for proprioception in regulation of primitives. However the in vivo behavior of spindle and golgi tendon receptors in frogs in response to vibration are not well described and the proportions of these proprioceptors are not established. In this study, we examine the selectivity of muscle vibration in the spinal frog. The aim of the study was (1) to examine how hindlimb muscle spindles and GTO receptors are activated by muscle vibration and (2) to estimate the relative numbers of GTO receptors and spindle afferents in a selected muscle, for comparison with the mammal. Single muscle afferents from the biceps muscle were identified in the dorsal roots. These were tested in response to biceps vibration, intramuscular stimulation and biceps nerve stimulation. Biceps units were categorized into two types: First, spindle afferents which had a high conduction velocity (approximately 20-30 m/s), responded reliably (were entrained 1:1) to muscle vibration, and exhibited distinct pauses to shortening muscle contractions. Second, golgi tendon organ afferents, which had a lower conduction velocity (approximately 10-20 m/s), responded less reliably to muscle vibration at physiologic muscle lengths, but responded more reliably at extended lengths or with background muscle contraction, and exhibited distinct bursts to shortening muscle contractions. Vibration responses of these units were tested with and without muscle curarization. Ensemble (suction electrode) recordings from the dorsal roots were used to provide rough estimates of the proportions of the two muscle afferent types.

Afferent mechanisms for the reflex response to imposed ankle movement in chronic spinal cord injury.

We have reported earlier that externally imposed ankle movements trigger ankle and hip flexion reflexes in individuals with spinal cord injury (SCI). In order to examine the afferent mechanisms underlying these movement-triggered reflexes, controlled ankle movements were imposed in 17 SCI subjects. In 13 of these subjects, reflex torques were recorded at the hip, knee and ankle in response to 5 ankle movement ranges, and 4 movement speeds. Subjects were tested using both ankle plantarflexion and dorsiflexion movements. The principal outcome measure, peak hip flexion torque of the induced reflexes, was used for comparing the effects of movement range and speed on the reflex response. We found that movement-triggered reflexes were sensitive to the angular range of ankle deflection, but insensitive to the velocity of the movement. Movement amplitudes sufficient to trigger hip and ankle flexion were routinely associated with increases in ankle passive force, suggesting that force-sensitive receptors participated in the reflex response. However, increases in angular range also corresponded to increases in muscle length, making it difficult to distinguish whether the response was triggered by a load-sensitive receptor (e.g., Golgi tendon organ or muscle free nerve ending) or a position-sensitive receptor responsive to absolute ankle angle (e.g., muscle spindle secondary afferent). The absence of velocity dependence of the reflex suggested that spindle Ia afferents were not major contributors. These results suggest movement-triggered reflexes originate in muscle receptors that are sensitive to either absolute muscle length, to muscle force or to both. Although receptors that are sensitive to absolute muscle length cannot be excluded with certainty, the finding that reflex responses require that ankle movements elicit an increase in passive force argues for a prominent role of nonspindle mechanoreceptors, such as group III/IV muscle afferents. These afferents are activated preferentially as muscles are stretched to near maximum length, and they appear to have potent reflex effects in spinal cord injury.

Formation of supernumerary muscle spindles at the expense of Golgi tendon organs in ER81-deficient mice.

ER81, a member of the ETS family of transcription factors, is essential for the formation of connections between sensory and motor neurons in the spinal cord. Mice lacking Er81 genes exhibit reduced monosynaptic sensory-motoneuron connectivity in response to muscle nerve stimulation. Proximal muscle nerve stimulation elicits fewer monosynaptic potentials than stimulation of distal nerves in hindlimbs, a deficit that is paralleled by a paucity of muscle spindles in proximal muscles (Arber et al., 2000). We examined whether a presence of spindles innervated by afferents in distal muscles correlated with the increased preservation of monosynaptic sensory-motor potentials in distal muscle nerves. Not only were spindles and Ia afferents present, but also they were supernumerary in distal muscles such as the soleus, medial gastrocnemius, and extensor hallucis longus. Concomitantly, a deficiency of Golgi tendon organs (GTOs) and Ib afferents was observed in distal muscles, as if supernumerary spindles formed at the expense of tendon organs in the absence of Er81. Thus, ER81 may be involved in mechanisms that regulate acquisition of the Ia and Ib phenotypes by subsets of proprioceptive muscle afferents. Segmental differences in muscle spindle and GTO dependence on ER81 suggest that more than one ETS transcription factor may participate in the regulation of limb proprioceptive system assembly in the mouse.

Elbow Flexor Inhibition as a Function of Muscle Length

Muscle inhibition (MI) in human knee extensors increases with increasing maximal voluntary force as a function of knee angle. It was speculated that this angle-dependent MI was modulated by force-dependent feedback, likely Golgi tendon organ pathways. Such angle-dependent MI is of clinical and theoretical importance. The purpose of this study was to determine MI in human elbow flexors for maximal voluntary contractions. Muscle inhibition, elbow flexor force, and electromyographic (EMG) activity were measured in 31 volunteers at elbow angles between 30º and 120º. MI and elbow flexor EMG were the same at all elbow angles. Maximal isometric forces were greatest at the 70º angle, and never fell below 70% of the peak force at any of the tested angles. From these results it is concluded that force-dependent modulation of MI did not occur in the elbow flexors, possibly because maximal isometric force remained relatively close (within 30%) to the peak force. In contrast, force-dependent modulation of MI occurred in the knee extensors at the most extended angles, when the average knee extensor force had dropped to 50% or less of the maximal knee extensor force. It is likely that human maximal voluntary contractions are not associated with a given activation. Rather, activation appears to be modulated by force-dependent feedback at force levels below 70% of the absolute peak force, which manifests itself in a change of MI that parallels the level of maximal isometric force in voluntary contractions.

The transduction properties of intercostal muscle mechanoreceptors.

Intercostal muscles are richly innervated by mechanoreceptors. In vivo studies of cat intercostal muscle have shown that there are 3 populations of intercostal muscle mechanoreceptors: primary muscle spindles (1 degrees ), secondary muscle spindles (2 degrees ) and Golgi tendon organs (GTO). The purpose of this study was to determine the mechanical transduction properties of intercostal muscle mechanoreceptors in response to controlled length and velocity displacements of the intercostal space. Mechanoreceptors, recorded from dorsal root fibers, were localized within an isolated intercostal muscle space (ICS). Changes in ICS displacement and the velocity of ICS displacement were independently controlled with an electromagnetic motor. ICS velocity (0.5 - 100 microm/msec to a displacement of 2,000 microm) and displacement (50-2,000 microm at a constant velocity of 10 microm/msec) parameters encompassed the full range of rib motion. Both 1 degrees and 2 degrees muscle spindles were found evenly distributed within the ICS. GTOs were localized along the rib borders. The 1 degrees spindles had the greatest discharge frequency in response to displacement amplitude followed by the 2 degrees afferents and GTOs. The 1 degrees muscle spindles also possessed the greatest discharge frequency in response to graded velocity changes, 3.0 spikes x sec(-1)/microm x msec(-1). GTOs had a velocity response of 2.4 spikes x sec(-1)/microm x msec(-1) followed by 2 degrees muscle spindles at 0.6 spikes x sec(-1)/microm x msec(-1). The results of this study provide a systematic description of the mechanosenitivity of the 3 types of intercostal muscle mechanoreceptors. These mechanoreceptors have discharge properties that transduce the magnitude and velocity of intercostal muscle length.