Feedforward stimulation

Figure 6.19 Regulation of the synthesis of glycogen from glucose in liver and muscle. Insulin is the major factor stimulating glycogen synthesis in muscle it increases glucose transport into the muscle and the activity of glycogen synthase, activity which is also activated by glucose 6-phosphate but inhibited by glycogen. The latter represents a feedback mechanism and the former a feedforward. The mechanism by which glycogen inhibits the activity is not known. The mechanism for the insulin effect is discussed in Chapter 12.

Pyruvate kinase is also stimulated by fructose 1,6-bisphosphate (see Topic J3 feedforward activation) so that its activity rises when needed, as glycolysis speeds up. 

In Section 4.4 was mentioned the additional mode of feedforward control. There are several places where biological control responses have the appearance of feedforward control. One of these is control of breathing during exercise. It is known that increasing the level of inhaled carbon dioxide at rest stimulates both the depth and frequency of breathing with the purpose of removing excess CO2 from the respiratory system. There is, however, a small portion of this CO2 that is not exhaled, and there is a small but measurable increase in CO2 dissolved in the blood (Johnson, 2007). 

Abbas, J.J. and Triolo, R.J. 1997. Experimental evaluation of an adaptive feedforward controller for use in functional neuromuscular stimulation systems. IEEE Trans. Rehabil. Eng., 5 12—22. 

Sloviter, RS (1991a) Feedforward and feedback inhibition of hippocampal principal cell activity evoked by perforant path stimulation GABA-mediated mechanisms that regulate excitability in vivo. Hippocampus, 1 31-40. 

---