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Fascial Anatomy
Published in David Lesondak, Angeli Maun Akey, 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.
The respiratory system
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
At the beginning of exercise, there is an immediate increase in ventilation. This increase is thought to be caused by two mechanisms involving the cerebral cortex. Neurons of the primary motor cortex stimulate alpha motor neurons in the spinal cord to cause skeletal muscle contraction. In addition, impulses from the motor cortex, transmitted through collateral interconnections to the medullary respiratory center, stimulate ventilation. The motor cortex is also involved in the stimulation of the cardiovascular system during exercise. These adjustments, which occur before any homeostatic factors (e.g., blood gases) have changed, are referred to as anticipatory adjustments. The immediate increase in ventilation may account for as much as 50% of the total ventilatory response to exercise. A conditioned reflex, or a learned response to exercise, may also be involved. Once again, impulses from the cerebral cortex provide input to the medullary respiratory center.
Impairment of functions of the nervous system
Published in Ramar Sabapathi Vinayagam, Integrated Evaluation of Disability, 2019
The descending input from the motor cortex modulates the intrinsic circuit existing in the spinal cord. The input from the intrinsic circuit either exerts an excitatory or inhibitory effect on alpha and gamma motor neurons. Interruption of these descending inputs results in increased activation of alpha and gamma motor neurons causing an increase in resting muscle tone. Alpha motor neurons activate the extrafusal muscle fibers, and any lesion in the alpha motor neurons results in decrease or loss of muscle tone (25). The “Modified Ashworth Scale” describes grading of hypertonia (26). Integrated Evaluation of Disability has developed a method to grade hypotonia of the muscle (Illustration 6.2).
The Influence of Experience on Neuromuscular Control of the Body When Cutting at Different Angles
Published in Journal of Motor Behavior, 2023
Zhengye Pan, Lushuai Liu, Xingman Li, Yunchao Ma
To describe the spinal motor output pattern, the 13 sEMG signals collected were mapped to the rostrocaudal location of the pool of alpha-motor neurons (MNs) in the ninth thoracic (T9) to the third sacral (S3) vertebral segments, with the thoracic segment (T9-12) predominantly innervating the trunk muscle groups and the lumbar (L1-5) and sacral (S1-3) segments predominantly innervating the lower limb muscle groups. The original sEMG signal is high-pass filtered (50 Hz), full-wave rectified and low-pass filtered (20 Hz) using a 4th-order IIR Butterworth zero-phase filter (Santuz et al., 2017a) based on Python (v3.9.13, Delawwere, US), and a linear envelope is constructed with amplitude normalisation based on maximum activation (Santuz et al., 2017b). In addition, artefacts in sEMG were removed using fastICA (Hu et al., 2007). The contribution of each muscle to the activity of the spinal cord segments is calculated using the neuromuscular map (Kendall et al., 2014). The motor output of each spinal cord segment Sj is estimated using the following equation, assuming a common spinal topography among the investigated participants: mj is the muscle innervated by each spinal cord segment, ni is the number of spinal cord segments innervating ith muscle, and kij is the weight factor of each muscle relative to the innervated spinal cord segment (la Scaleia et al., 2014).
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
Stretching can help prevent complications following UMN lesions that can be explained by the neurophysiological effects, the effects of viscoelastical properties, stiffness and ROM, and preventing contractures.15 The neurophysiological effects of stretching on spasticity showed that such effect may be best explained by a change in the excitability of motor neurons within the spastic muscle.16,17 Spasticity develops when an imbalance occurs in the excitatory and inhibitory input to alpha motor neurons (αMN) and more specifically from the loss of inhibition of motor neurons. In response to muscle tension, afferents from the Golgi tendon organs are normally influenced by corticospinal fibers that causes its associated muscle to relax (inhibition) and thereby assists in regulating muscle contraction force.18 Such inhibition is easily demonstrated in healthy subjects but failed to produce on the paretic side in UMN lesion patients.19 In case of spasticity, there is greater increase in excitability of spinal neural function during muscle stretching because of short-latency autogenic inhibition (IB inhibition)20 Ib afferent inhibitory neurons are not fired under short stretching durations. Therefore, UMN lesion patients require longer durations of continuous stretching of the affected hypertonic muscle to fire the Ib inhibitory neurons.21 With regard to viscoelastical properties, even though studies have methodological limitations,15 Some studies showed that stretching reduced the viscoelastic components of the ankle joint muscles.11,22
Current and emerging ALS biomarkers: utility and potential in clinical trials
Published in Expert Review of Neurotherapeutics, 2018
Arens Taga, Nicholas J. Maragakis
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with the progressive loss of both corticospinal (upper motor neurons – UMN) and alpha motor neurons (lower motor neurons – LMN) as core features but the degeneration of other neuronal subtypes occurs as well. Clinical and pathogenic heterogeneity with regard to anatomical sites of disease onset and progression overtime are important features of the disease. Despite a host of clinical trials targeting ALS, only two drugs (riluzole and edaravone) have become widely available as disease modifying therapies [1,2]. In light of recurrent failures in clinical trials for ALS, there has been a groundswell of interest in revisiting drug development strategies and clinical trials designs. Biomarkers are relevant to both, as shown by therapeutic efforts and successes in other diseases.