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Functional Neurology
Published in James Crossley, Functional Exercise and Rehabilitation, 2021
Scientists have identified two chief proprioceptors embedded within muscle, the muscle spindles and Golgi tendon organs (GTOs). In the 1960s and 1970s, scientists identified muscle spindles running along the length of muscle fibers. Muscle spindles provide the brain with sensory information regarding stretch and the rate of stretch of muscle. They also give information regarding the stress and strain passing through muscles as they ‘deform’ under load.
Skeletal Muscle
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
The muscle spindle is a fusiform capsule that is 4–10 mm long and 80–200 µm in diameter. It is a complex sensory organ that is richly innervated with both sensory and motor nerve fibers, accounting for more than two thirds of the myelinated fibers that innervate muscle. Human muscles contain 35–500 muscle spindles per muscle, with few exceptions, such as the muscles of the middle ear, which do not have any muscle spindles. The number of muscle spindles relative to the muscle mass is high in the small muscles of the neck, the muscles of the hand, and in the extraocular muscles of the eyes, reflecting, respectively, the need for fine movements in positioning of the head, manipulating objects, and in moving the eyes. Muscle spindles are generally scattered widely in the muscle body and are attached at both ends to the muscle connective tissue so as to be in parallel with the muscle fibers.
Muscle Spindles, Golgi Tendon Organs and Spinal Reflexes
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Motor innervation of the muscle spindle consists of γ-motor neurons that innervate the intrafusal fibres. The γ-motor neurons have two main roles in regulating muscle spindle sensitivity: (i) to adjust the sensitivity required by different muscle loading conditions and (ii) to maintain the sensitivity of the muscle spindle during muscle shortening. Stimulation of the γ-motor neurons produces contraction of the polar regions of the intrafusal fibres, which in turn stretches the central (equatorial) region of the intrafusal fibres. This alters the sensitivity of the muscle spindle to stretching of the whole muscle. There are two types of γ-motor neurons: (i) those associated with plate endings found at the ends or poles of both nuclear bag and nuclear chain fibres and (ii) those associated with trail endings which are found mainly on nuclear chain fibres. The γ-plate and nuclear bag-1 fibres are associated with dynamic γ-motor neurons. The dynamic motor neurons increase the dynamic sensitivity of the endings so that they are more sensitive to the velocity and the changes in the velocity of movement. The γ-trail nerves supplying nuclear bag-2 and nuclear chain fibres are associated with γ-motor neurons’ static activity (Figure 13.3). The static motor neurons therefore increase the static sensitivity of the endings, the slow adapting component of the response.
Effect of robotic-assisted ankle training on gait in stroke participants: A case series study
Published in Physiotherapy Theory and Practice, 2022
Gonzalo Varas-Diaz, Paul Cordo, Shamali Dusane, Tanvi Bhatt
Muscle vibration is a potent and selective stimulus for muscle spindle Ia afferents (Burke, Hagbarth, Lofstedt, and Wallin, 1976), which are sensory receptors that provide the brain with a key source of proprioceptive input to control movement. Vibration has been shown to rapidly increase cortical somatosensory representations of the vibrated body part (Forner-Cordero et al., 2008) and to improve motor coordination in persons following stroke (Marconi et al., 2011; Noma et al., 2009; Paoloni et al., 2010). In the absence of proprioception, coordinated movement and motor learning are severely compromised, as seen in people with pan-sensory neuropathy (Gandevia and Burke, 1992). Mechanical vibration applied to a muscle at a stationary joint at frequencies between 30–70 pulses/s (Cordo et al., 1993) can evoke simultaneous illusions of static joint displacement and continuous motion (i.e., velocity) (Gandevia and Burke, 1992; Goodwin, McCloskey, and Matthews, 1972) consistent with elongation of the vibrated muscle(s). During movement, if vibration is applied to a muscle while it is being elongated, the perceived displacement and velocity of motion is enhanced. The interventional device used in this study employs vibration during muscle lengthening as a means of selectively augmenting proprioceptive feedback of the assisted motion to the brain during training.
The relationship between eccentric hamstring strength and dynamic stability in elite academy footballers
Published in Science and Medicine in Football, 2021
David Rhodes, Josh Jeffrey, Joe Maden-Wilkinson, Antony Reedy, Erin Morehead, John Kiely, Daniel Birdsall, Chris Carling, Jill Alexander
During functional performance, changes in muscle length or alterations in knee position initiate a stabilisation response, due to the stimulation of mechanoreceptors within the joint or the muscle (Melnyk and Gollhofer 2007). Key receptors responsible for this afferent response include Muscle Spindles, Golgi Tendon Organs (GTO’s), Ruffini Endings, Ruffini Corpuscles and Pacinian Corpuscles (Changella et al. 2012; Lee et al. 2015). As to which receptors stimulate the afferent signal, however, is arguably irrelevant, as proprioceptive responses from the mechanoreceptors within the joint and muscle are likely to occur at the same time. Reducing injury risk associated with the hamstrings and the knee is reliant on the muscle’s ability to generate the required effected functional response (Rhodes et al. 2018).
The evidence for prolonged muscle stretching in ankle joint management in upper motor neuron lesions: considerations for rehabilitation – a systematic review
Published in Topics in Stroke Rehabilitation, 2019
PMS is one of the commonly used interventions in the management of complications following UMN lesions.3,9,11,12 The term “prolonged stretching” is defined as the process of placing particular body segments into a position that will lengthen, or elongate, the muscles and associated soft tissues over an extended period of time. Different stretching techniques have been used in neurological rehabilitation,13 prolonged stretching produces inhibition of muscle responses, which may reduce spasticity and thereby preventing the loss in range of motion; although it is not entirely clear how these responses are produced. At the neurological level, prolonged stretching appears to have an influence on the neural components of the muscle, the Golgi Tendon Organs, and Muscle Spindles. At the structural level, Prolonged lengthening of the sarcomeres, the contractile units within muscle, leads to increased soft tissue length due to an increased number of sarcomeres in series. On the other hand, ligaments, joint capsule, and fascia, the non-contractile units of muscle, consist of collagen and elastin fibers. Prolonged lengthening of these non-contractile units may cause permanent tissue deformation and consequential tissue lengthening.14