Detection of epimuscular myofascial forces by Golgi tendon organs

Skeletal muscles embed multiple tendon organs, both at the proximal and distal ends of muscle fibers. One of the functions of such spatial distribution may be to provide locally unique force feedback, which may become more important when stresses are distributed non-uniformly within the muscle. Forces exerted by connections between adjacent muscles (i.e. epimuscular myofascial forces) may cause such local differences in force. The aim of this exploratory study was to investigate the effects of mechanical interactions between adjacent muscles on sensory encoding by tendon organs. Action potentials from single afferents were recorded intra-axonally in response to ramp-hold release (RHR) stretches of a passive agonistic muscle at different lengths or relative positions of its passive synergist. The tendons of gastrocnemius (GAS), plantaris (PL) and soleus (SO) muscles were cut from the skeleton for attachment to servomotors. Connective tissues among these muscles were kept intact. Lengthening GAS + PL decreased the force threshold of SO tendon organs (p = 0.035). The force threshold of lateral gastrocnemius (LG) tendon organs was not affected by SO length (p = 0.371). Also displacing LG + PL, kept at a constant muscle–tendon unit length, from a proximal to a more distal position resulted in a decrease in force threshold of LG tendon organs (p = 0.007). These results indicate that tendon organ firing is affected by changes in length and/or relative position of adjacent synergistic muscles. We conclude that tendon organs can provide the central nervous system with information about local stresses caused by epimuscular myofascial forces.

Structural and Biological Basis for Proprioception

The proprioception is the sense of positioning and movement. It is mediate by proprioceptors, a small subset of mechanosensory neurons localized in the dorsal root ganglia that convey information about the stretch and tension of muscles, tendons, and joints. These neurons supply of afferent innervation to specialized sensory organs in muscles (muscle spindles) and tendons (Golgi tendon organs). Thereafter, the information originated in the proprioceptors travels throughout two main nerve pathways reaching the central nervous system at the level of the spinal cord and the cerebellum (unconscious) and the cerebral cortex (conscious) for processing. On the other hand, since the stimuli for proprioceptors are mechanical (stretch, tension) proprioception can be regarded as a modality of mechanosensitivity and the putative mechanotransducers proprioceptors begins to be known now. The mechanogated ion channels acid-sensing ion channel 2 (ASIC2), transient receptor potential vanilloid 4 (TRPV4) and PIEZO2 are among candidates. Impairment or poor proprioception is proper of aging and some neurological diseases. Future research should focus on treating these defects. This chapter intends provide a comprehensive update an overview of the anatomical, structural and molecular basis of proprioception as well as of the main causes of proprioception impairment, including aging, and possible treatments.

Errors in Predicting Muscle Fiber Lengths from Joint Kinematics Point to the Need to Include Tendon Tension in Computational Neuromuscular Models

Accurate predictions of tendon forces must consider musculotendon mechanics; specifically muscle fiber lengths and velocities. These are either predicted explicitly by simulating musculoskeletal dynamics or approximated from measured limb kinematics. The latter is complicated by the fact that tendon lengths and pennation angles vary with both limb kinematics and tendon tension. We now derive the error in kinematically-approximated muscle fiber lengths as a general equation of muscle geometry and tendon tension. This enables researchers to objectively evaluate this error’s significance—which can reach ~ 80% of the optimal muscle fiber length—with respect to the scientific or clinical question being asked. Although this equation provides a detailed functional relationship between muscle fiber lengths, joint kinematics and tendon tension, the parameters used to characterize musculotendon architecture are subject- and muscle-specific. This parametric uncertainty limits the accuracy of any generic musculoskeletal model that hopes to explain subject-specific phenomena. Nevertheless, the existence of such a functional relationship has profound implications to biological proprioception. These results strongly suggest that tendon tension information (from Golgi tendon organs) is likely integrated with muscle fiber length information (from muscle spindles) at the spinal cord to produce useful estimates of limb configuration to enable effective control of movement.

Acute effects of contract-relax proprioceptive neuromuscular facilitation stretching of hip abductors and adductors on dynamic balance

Background Balance control has been shown to play a fundamental role both in everyday life and many athletic activities. An important component of balance control is the somatosensory information gained from muscle spindles and Golgi tendon organs. The changes in the muscle-tendon unit stiffness could alter the ability to detect and respond promptly to changes of an unstable environment. One of the procedures affecting muscle stiffness is stretching, and contract-relax PNF stretching (CRS) is considered as one of the safest and most effective techniques. So far, there are no studies on the impact of CRS of hip adductor and abductor muscles on body balance. These muscle groups are responsible for maintaining mediolateral balance which is of particular interest, since it is more affected by ageing and disease and since its deterioration has been associated with an increased risk of falling. In light of the above, the aim of the present study was to investigate the effects of a single dose of contract-relax proprioceptive neuromuscular facilitation stretching of hip adductors and abductors on mediolateral dynamic balance. Methods The study involved 45 healthy individuals (age 19–23 years) assigned to the intervention group (IG) or the control group (CG). Balance testing was carried out before (Pre) and immediately after CRS in the intervention group or after 5-minute rest in the control group (Post). There were performed three repetitions of the CRS targeting the adductor and abductor muscles of the hip. Results Statistically significant differences between Pre and Post condition were observed only in the intervention group. The values of all measured variables defining the body’s dynamic balance were significantly lower immediately after the applied CRS, which indicates an improved body balance: Global Index (p = 0.0001), total area of sway (p = 0.0001), external area of sway (p = 0.00004), external time (p = 0.0004) and reaction time (p = 0.0003). Conclusions A single dose of contract-relax proprioceptive neuromuscular facilitation stretching of the hip adductor and abductor muscles improved mediolateral dynamic balance.

New functions for the proprioceptive system in skeletal biology

Muscle spindles and Golgi tendon organs (GTOs) are two types of sensory receptors that respond to changes in length or tension of skeletal muscles. These mechanosensors have long been known to participate in both proprioception and stretch reflex. Here, we present recent findings implicating these organs in maintenance of spine alignment as well as in realignment of fractured bones. These discoveries have been made in several mouse lines lacking functional mechanosensors in part or completely. In both studies, the absence of functional spindles and GTOs produced a more severe phenotype than that of spindles alone. Interestingly, the spinal curve phenotype, which appeared during peripubertal development, bears resemblance to the human condition adolescent idiopathic scoliosis. This similarity may contribute to the study of the disease by offering both an animal model and a clue as to its aetiology. Moreover, it raises the possibility that impaired proprioceptive signalling may be involved in the aetiology of other conditions. Overall, these new findings expand considerably the scope of involvement of proprioception in musculoskeletal development and function.This article is part of the Theo Murphy meeting issue ‘Mechanics of development’.

Distributed force feedback in the spinal cord and the regulation of limb mechanics

This review is an update on the role of force feedback from Golgi tendon organs in the regulation of limb mechanics during voluntary movement. Current ideas about the role of force feedback are based on modular circuits linking idealized systems of agonists, synergists, and antagonistic muscles. In contrast, force feedback is widely distributed across the muscles of a limb and cannot be understood based on these circuit motifs. Similarly, muscle architecture cannot be understood in terms of idealized systems, since muscles cross multiple joints and axes of rotation and further influence remote joints through inertial coupling. It is hypothesized that distributed force feedback better represents the complex mechanical interactions of muscles, including the stresses in the musculoskeletal network born by muscle articulations, myofascial force transmission, and inertial coupling. Together with the strains of muscle fascicles measured by length feedback from muscle spindle receptors, this integrated proprioceptive feedback represents the mechanical state of the musculoskeletal system. Within the spinal cord, force feedback has excitatory and inhibitory components that coexist in various combinations based on motor task and integrated with length feedback at the premotoneuronal and motoneuronal levels. It is concluded that, in agreement with other investigators, autogenic, excitatory force feedback contributes to propulsion and weight support. It is further concluded that coexistent inhibitory force feedback, together with length feedback, functions to manage interjoint coordination and the mechanical properties of the limb in the face of destabilizing inertial forces and positive force feedback, as required by the accelerations and changing directions of both predator and prey.

Patterns of intermuscular inhibitory force feedback across cat hindlimbs suggest a flexible system for regulating whole limb mechanics

Prior work has suggested that Golgi tendon organ feedback, via its distributed network linking muscles spanning all joints, could be used by the nervous system to help regulate whole limb mechanics if appropriately organized. We tested this hypothesis by characterizing the patterns of intermuscular force-dependent feedback between the primary extensor muscles spanning the knee, ankle, and toes in decerebrate cat hindlimbs. Intermuscular force feedback was evaluated by stretching tendons of selected muscles in isolation and in pairwise combinations and then measuring the resulting force-dependent intermuscular interactions. The relative inhibitory feedback between extensor muscles was examined, as well as symmetry of the interactions across limbs. Differences in the directional biases of inhibitory feedback were observed across cats, with three patterns identified as points on a spectrum: pattern 1, directional bias of inhibitory feedback onto the ankle extensors and toe flexors; pattern 2, convergence of inhibitory feedback onto ankle extensors and mostly balanced inhibitory feedback between vastus muscle group and flexor hallucis longus, and pattern 3, directional bias of inhibitory feedback onto ankle and knee extensors. The patterns of inhibitory feedback, while different across cats, were symmetric across limbs of individual cats. The variable but structured distribution of force feedback across cat hindlimbs provides preliminary evidence that inhibitory force feedback could be a regulated neural control variable. We propose the directional biases of inhibitory feedback observed experimentally could provide important task-dependent benefits, such as directionally appropriate joint compliance, joint coupling, and compensation for nonuniform inertia. NEW & NOTEWORTHY Feedback from Golgi tendon organs project widely among extensor motor nuclei in the spinal cord. The distributed nature of force feedback suggests these pathways contribute to the global regulation of limb mechanics. Analysis of this network in individual animals indicates that the strengths of these pathways can be reorganized appropriately for a variety of motor tasks, including level walking, slope walking, and landing.

Respiratory

This chapter describes the pathophysiology of the respiratory system as it applies to Emergency Medicine, and in particular the Primary FRCEM examination. The chapter outlines the key details of the control of ventilation, reflexes, pressure, chemical, and irritant receptors, J receptors, pulmonary stretch receptors, Golgi tendon organs, muscle spindles, lung volumes, pulmonary mechanics, oxygen and carbon dioxide transport, DO2/VO2 relationships, carbon monoxide, pulse oximetry, effects of altitude, and dysbarism. This chapter is laid out exactly following the RCEM syllabus, to allow easy reference and consolidation of learning.