The nervous system
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella in Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
The multineuronal (extrapyramidal) tracts originate in many regions of the brain including the motor regions of the cerebral cortex, the cerebellum, and the basal ganglia. Impulses from these various regions are transmitted to nuclei in the brainstem, in particular, the reticular formation and the vestibular nuclei. The axons of neurons in these nuclei descend to the alpha motor neurons in the spinal cord. Therefore, in contrast to the corticospinal tracts, these pathways are polysynaptic. The multineuronal tracts regulate overall body posture, balance and walking. Specifically, these tracts control subconscious movements of large muscle groups in the trunk and in the limbs. Some of the pathways originating in the brainstem cross to the other side of the spinal cord to affect muscles on the opposite side of the body. However, most remain uncrossed (e.g., vestibulospinal tract, Table 13.5).
Drug-Related Sarcopenia
Kohlstadt Ingrid, Cintron Kenneth in Metabolic Therapies in Orthopedics, Second Edition, 2018
There is a neurological component to sarcopenia that results in the loss of alpha motor-neuron axons. This decreases the electro-physical nerve velocity, which reduces intermodal length and segmental demyelization that occurs throughout the aging process.4 The role of demyelization in sarcopenia seems minor, but the progressive demyelization and renervation process that is observed throughout aging and resulting fiber type grouping is the primary mechanism that is involved in the development of sarcopenia among patients.4 The loss of alpha motor neurons leads to an effect in the types of neurons in the lower extremities, which can lead to less coordinated muscle action and a reduction in muscle strength.4 This is related to the loss of type II fast fibers throughout aging.
The Consciousness of Muscular Effort and Movement
Max R. Bennett in The Idea of Consciousness, 2020
The kind of information in the signals processed by the somatosensory cortex may require that the muscles that gave rise to the sensory input in the first place be contracted. In this case, neurons in the part of the cortex concerned with contracting muscles, namely the motor cortex, project a signal to the appropriate motor neurons in the spinal cord with synaptic connections to these muscles. These are of two different kinds: alpha motor neurons that have synaptic attachments to cells in the muscles in question that produce the force, and gamma motor neurons that have synaptic connections with cells that contract in the sensory receptor apparatus itself. Contraction of this latter type of cell changes the characteristics of the sensory receptors so that they rapidly send signals to the sensory neurons outside the spinal cord and from there to the alpha motor neurons, leading to the contraction of the bulk of the muscle cells. The sensory receptors also send signals to the somatosensory cortex via the thalamus along the pathway already described.
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
Relationship between soleus H-reflex asymmetry and postural control in multiple sclerosis
Published in Disability and Rehabilitation, 2022
Gregory S. Cantrell, David J. Lantis, Michael G. Bemben, Chris D. Black, Daniel J. Larson, Gabriel Pardo, Cecilie Fjeldstad-Pardo, Rebecca D. Larson
The Hoffmann reflex (H-reflex) is an electrical stimulation-induced analogue of the monosynaptic reflex elicited by activation of group Ia sensory fibers [12]. Maximal H-reflex amplitude (Hmax) compared with maximal motor response (Mmax) resulting from direct activation of alpha-motor neurons has been previously used to assess spinal excitability of motor neurons. Moreover, the soleus H-reflex is one of the more commonly studied reflexes in spinal excitability investigations, due to the convenient accessibility of the tibial nerve [12,13], and was of interest in the present study due to its role in posture. While the soleus H-reflex has been assessed in people with MS [5,14], it has not yet been compared between legs, nor has a potential link between soleus H-reflex asymmetry and postural stability in people with MS been evaluated. Therefore, supported by previous research demonstrating bilateral asymmetries in people with MS, the purpose of this study was to test the hypotheses that the soleus H-reflex differs between legs in people with MS, and soleus H-reflex asymmetry is associated with postural control.
Related Knowledge Centers
- Brainstem
- Extrafusal Muscle Fiber
- Gamma Motor Neuron
- Intrafusal Muscle Fiber
- Lower Motor Neuron
- Muscle Contraction
- Muscle Spindle
- Spinal Cord
- Skeletal Muscle
- Multipolar Neuron