Physiology of excitable cells
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2015
Sensory receptors include exteroreceptors, interoreceptors and proprioceptors. In general, sensory transduction is accomplished by the production of a receptor potential and encode modality, spatial localization, intensity, duration and frequency of stimuli. Sensory receptors may show accommodation. Muscle spindles are sensory receptors in skeletal muscles that lie parallel to the regular extrafusal muscle fibres. They consist of nuclear bag and nuclear chain intrafusal fibres. Ia afferent fibres form primary nerve endings on both nuclear bag and chain fibres. Group II afferent fibres form a secondary ending, which is found chiefly on the nuclear chain fibres. Primary endings detect static (change in length) and dynamic (rate of change in muscle length) changes in muscle, whereas secondary endings detect only static responses. The γ efferent system controls the sensitivity of the muscle spindle. The muscle spindles also dampen jerky or oscillatory muscle contractions. The Golgi tendon organs, located in the tendons of the muscles, are arranged in series with the skeletal muscle. They are supplied by IIb afferent fibres and are stimulated by both stretch and contraction of the muscle. The stretch reflex includes a monosynaptic excitatory pathway from muscle spindle afferent (Ia and II) fibres to the α motor neurons to the same and synergistic muscle and a disynaptic inhibitory pathway to the motor neurons of the antagonist muscles.
Fascial Anatomy
David Lesondak, Angeli Maun Akey in Fascia, Function, and Medical Applications, 2020
Another important function of muscle spindles is the pre-activation of the motor units. When a muscle contracts, two motor nerves from the central nervous system are involved: the alpha motor neuron, which is responsible for the muscle contraction, and the gamma motor neuron, whose main responsibility is to activate (in this case stretch) the spindle cell. It is hypothesized that activation of the intrafusal fibers will contract the capsule of the muscle spindle that will stretch the adjoining perimysium and epimysium. Deformation of the spindle cell capsule stimulates the annulospiral (flower spray) endings of the Ia fibers and type II fibers, all of which generate input to the spinal cord. If no peripheral or central inhibition occurs, activation of the alpha motor neuron will take place. This activation will generate the contraction of the extrafusal fiber of the motor units, creating what is called a gamma loop, essentially a feedback loop that regulates muscle tension.
Sensory contributions to control
Andrea Utley in Motor Control, Learning and Development, 2018
Muscle spindles are found in most skeletal muscles but are particularly concentrated in muscles that exert fine motor control (e.g. the small muscles of the hand) and large muscles, which are rich in slow twitch muscle fibers. As its name implies, a muscle spindle is a spindle-shaped organ composed of a bundle of modified muscle fibers innervated by both sensory and motor axons. Muscle spindles lie in parallel in between regular muscle fibers, the distal ends being attached to the connective tissue within the muscle. Muscle spindles are stretch receptors, and when the muscle is stretched the spindle increases the discharge rate of the afferent fibers. This sends a message to a motor neuron in the spinal cord, which in turn relays a message to the muscle causing a contraction and thus shortens the muscle (e.g. the knee-jerk reflex, see Chapter 14).
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.
Use of virtual reality intervention to improve reaction time in children with cerebral palsy: A randomized controlled trial
Published in Developmental Neurorehabilitation, 2018
Morteza Pourazar, Fatemeh Mirakhori, Rasool Hemayattalab, Fazlolah Bagherzadeh
Despite the multitude of literature describing information processing abilities of the nonhandicapped,7–10 little attention has focused on understanding how special populations, specifically those with cerebral palsy (CP), process incoming information for executing motor actions. CP describes a group of movements and posture that are attributed to nonprogressive impairments in the developing fetal or infant brain.11 Spastic Hemiplegic Cerebral Palsy (SHCP) is one of the most common forms of CP caused by unilateral damage to the motor cortex or pyramidal pathway.12 Unilateral muscles in the other side of the body (with respect to the damaged brain) are affected by spasms and cramps, and proprioception in the affected organs is impaired.12 As a result of these changes, movements in the affected side become slow, jerky, and alternative.12 Abnormalities in the information—processing mechanism which connects central nervous system to the muscle spindles have been considered.13,14 Individuals with CP have difficulties in regulating muscular activities related not only to voluntary movements, but also before starting the movements.15 It seems that RT in these people is influenced by the slower preparatory process in central nervous system.13,14
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
Related Knowledge Centers
- Central Nervous System
- Motor Neuron
- Muscle Contraction
- Proprioception
- Stretch Receptor
- Stretch Reflex
- Skeletal Muscle
- Afferent Nerve Fiber
- Type Ia Sensory Fiber
- Type II Sensory Fiber