Muscles as Actuators in Controlled Systems

8 Muscles as Actuators in Controlled Systems Servo Assistance in the Control of Extension 

Numerous control mechanisms take place in the arm musculature when we guide a glass of water to our mouth. Muscle contraction receptors (muscle spindles) effect servo assistance. The process can be described by four steps (Fig. 9.19). 

The extrafusal fibers EF of the muscle M and the intrafusal fibers IF of the muscle spindles MS contract simultaneously when commanded by the central nervous system G. 

The feedback signal sent via nerve fibers (so-called la-afference) remains constant for equivalent reduction in length of EF and IF the spindle control loop is inactive. 

Disturbances induced for example by unexpected increases or reductions in the load L cause the sensor ends SE in the muscle spindles to stretch or become compressed. 

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