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Control of Movement and Learning of Motor Skill
Published in Robert W. Proctor, Van Zandt Trisha, Human Factors in Simple and Complex Systems, 2018
Robert W. Proctor, Van Zandt Trisha
The spinal cord controls certain actions by way of spinal reflexes (Abernethy et al., 2013; Bonnet, Decety, Jeannerod, & Requin, 1997). Such reflexes begin with stimulation of the sensory receptors that provide information about limb position (proprioception). Proprioceptive receptors are located within the muscles, tendons, joints, and skin. Their signals are sent to the spinal cord, where a motor signal is quickly evoked and sent to the appropriate muscles. Spinal reflexes allow movements to be made within milliseconds of the initiating stimulus. For example, when a sensory neuron receives a painful signal, the limb withdrawal reflex will cause the appropriate muscle to contract, removing the limb from the source of the pain. This happens very quickly because the signal does not have to travel all the way to the brain and then back again.
Spinal Cord and Reflexes
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
The flexion reflex, also known as the withdrawal reflex, moves a limb away from a harmful, or noxious, stimulus. Suppose, for example, that one accidentally touches a hot plate (Figure 11.8). This activates cutaneous thermoreceptors, resulting in APs traveling to the spinal cord over afferent nerve fibers and innervating interneurons in the spinal cord. Although, for simplicity, a single interneuron is shown in the reflex arc in Figure 11.8, several populations of both excitatory and inhibitory interneurons are in fact involved, making the reflex polysynaptic. The afferent input, acting through interneurons, eventually reaches α-motoneurons that mediate the following responses: Excitation of the α-motoneurons that innervate the homonymous flexor muscles of the arm, where the homonymous muscles are those that are directly associated with the receptors that initiate the reflex. This leads to the withdrawal of the arm away from the hot plate. A more intense stimulus may excite the α-motoneurons that cause internal rotation of the shoulder (Section 9.3.4). In withdrawing the arm from the painful stimulus, the muscles of the arm and shoulder act as synergist muscles. It may be noted that the intensity of the stimulus is coded both in the mean frequency of APs as well as the number of afferent fibers activated. Thus, a more intense stimulus will stimulate receptors over a larger area of the skin, which activates a larger number of afferent fibers in parallel. This parallelism in the organization of the nervous system is not portrayed by single-line diagrams such as Figure 11.8.Concomitant with the excitation of the flexor α-motoneurons, the interneurons inhibit the α-motoneurons innervating the extensor muscles (Figure 11.8), as explained in connection with Ia interneurons (Section 11.2.2.2). This leads to relaxation of the extensor muscles that are antagonists to the contracting flexor muscles – an example of reciprocal inhibition referred to earlier.Withdrawal of a limb from a noxious stimulus generally involves some postural adjustments. This is most easily seen when the foot is withdrawn from a noxious stimulus. Elevation of the foot shifts the weight of the body to the contralateral leg on the other side of the body. The extensor muscles of this leg, which are the antigravity muscles, should contract, and the flexor muscles inhibited in order to support the additional load. Therefore, the afferent input should also activate interneurons that excite extensor α-motoneurons, and inhibit α-motoneurons of the contralateral leg. This is an additional reflex, resulting from the flexion reflex, and is referred to as the crossed extension reflex, or the crossed extensor reflex.
Methods and strategies of tDCS for the treatment of pain: current status and future directions
Published in Expert Review of Medical Devices, 2020
Kevin Pacheco-Barrios, Alejandra Cardenas-Rojas, Aurore Thibaut, Beatriz Costa, Isadora Ferreira, Wolnei Caumo, Felipe Fregni
Modeling studies [167] have showed a direct and longitudinal current density and electric field along the spinal cord, suggesting a feasible transcutaneous stimulation of multiple spinal cord segments. From preclinical studies, anodal ts-DCS has been proven to inhibit nociceptive responses, such as the nociceptive withdrawal reflex [168], the NWR temporal summation threshold [169], and laser-evoked potential amplitude [170]. The hypothesized mechanism involved in this modulation could be a direct or supraspinal-mediated change in excitability (NMDA-mediated plasticity) of spinal sensory neurons, including the wide dynamic range (WDR) neurons, which are involved in the spinal cord pain processing as well as in and the genesis and maintenance of chronic pain [169]. In summary, tsDCS could modulate neuronal activity in lemniscal, spinothalamic, and segmental spinal circuits, by glutamatergic system involvement, and ultimately modifying spinal cord plasticity [171] .
Effect of gait distance during robot training on walking independence after acute brain injury
Published in Assistive Technology, 2023
Gakuto Kitamura, Manabu Nankaku, Takayuki Kikuchi, Hidehisa Nishi, Hiroki Tanaka, Toru Nishikawa, Honami Yonezawa, Taishi Kajimoto, Takumi Kawano, Ayumi Ohtagaki, Eriko Mashimoto, Susumu Miyamoto, Ryosuke Ikeguchi, Shuichi Matsuda
In the present study, FAC improved significantly after intervention [mean (standard deviation, SD): from 0.8 (0.8) pre-intervention to 2.0 (1.3) post-intervention]. The results of this study are consistent with those of a recent systematic review of conventional gait training in the acute phase (Mehrholz et al., 2020). In addition, the improvement in FAC in this study was comparable to that of gait training with nociceptive withdrawal reflex (Spaich et al., 2014). In comparison to the current study, the previous study involved greater intervention (20 sessions of 30 min of gait training combined with 40 min of conventional physical therapy, five days a week). Consequently, it appears that the HAL gait training is effective with fewer sessions. Another study of ordinary physical therapy reported that FAC improved after intervention [mean (SD):0.4 (0.5) pre-intervention vs. 1.4 (0.8) post-intervention] as a result of 100 min a day conducted five times a week for 2 weeks in 34 patients [mean age (SD):59.7 (12.1) years] within 1 month after stroke onset [mean (SD):18.2 (5) days] (Chang et al., 2012). Their results elucidated the contribution of spontaneous recovery and/or conventional rehabilitation to FAC improvement. In this study, FAC improvement may have been affected by the relatively younger age of the patients [mean (SD): 56.0 (19.0) years]. Compared with the previous study, even considering the influence of patient age on FAC improvement, the change in FAC in the present study seems to be efficient. However, it is unclear how much of an additive effect was obtained by gait training with the HAL because there was no control group, such as a group receiving only conventional rehabilitation, in the present study.