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Spinal Cord and Reflexes
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Also known as the inverse myotatic reflex and autogenic inhibition, the reflex arc comprises the Golgi tendon organs (GTOs) as the receptors (Section 9.4.1), Ib afferent fibers terminating on Ib-interneurons, the α-motoneurons of the homonymous muscle, and the muscle itself, as illustrated in Figure 11.10. The Ib afferents excite Ib-interneurons that inhibit α-motoneurons, making the reflex disynaptic. As in the case of the stretch reflex, the effect of the sensory fibers, which is inhibitory in this case, is exerted on synergist muscles as well, and inhibition of the α-motoneurons of the agonist muscles leads to excitation of the α-motoneurons of the antagonist muscles. This occurs through excitation by Ib fibers of excitatory interneurons that excite the α-motoneurons of the antagonist muscles, and is an example of reciprocal innervation, a special case of which being reciprocal inhibition.
Feedback Control to a Static Target Angle in the Middle Finger Metacarpophalangeal Joint Using Functional Electrical Stimulation
Published in International Journal of Human–Computer Interaction, 2020
Kyosuke Watanabe, Makoto Oka, Hirohiko Mori
Humans perform physical movements by controlling muscles in two manners. First, humans control the direction of joint movement by reciprocal innervation, which contracts the main muscle, which leads the movement, and relaxes the antagonist muscle located on the opposite side of the main muscle (Ito, 1986). Second, humans perform detailed physical movements via the co-contraction of antagonistic muscles which leads to an increase in the stiffness of the joint (Gribble et al., 2003). Atsuumi et al. (2018) defined the ratio of the electrical stimulation intensity to the flexor digitorum muscle and the extensor digitorum muscle as the muscle antagonist ratio, and the sum was the muscle activity, and modeled a system with the muscle antagonist ratio as input and the force of the fingertips as output. The force of the fingertips was well estimated using the model. Therefore, we adopted the two concepts of muscle antagonist ratio and muscle antagonistic sum, referring to the research by Atsuumi et al. (2018). Atsuumi et al. (2018) defined the muscle antagonistic ratio based on the electrical stimulation intensity to each muscle; however, as described in section 4.1, there is a non-linearity relationship between the input dead zone and the muscle contraction force increase zone. Therefore, we defined the muscle antagonistic ratio and muscle antagonistic sum based on the force acting on the middle finger MP joint generated via electrical stimulation to the muscles. A formula for calculating the muscle antagonist ratio is as follows: