State space for different initial conditions

When fixed, the number of receptors ro is a scale parameter and it does not affect the stability. When r0 is not fixed but changes as a result of pharmacological interventions or pathological states, the operating point will, of course, change. 

When r (t) and ro are varying and the other parameters are fixed, simulations (not presented here) with (11.1) and (11.2) reveal that a decrease in r (t) results in a decrease in distance between P2 and P3. Conversely, an increase in ro results in a decrease in distance between Pi and P2.  

The above-mentioned theorem allows speculation about a monotone feedback curve and a nonlinear binding curve. Their intersections will have derivatives with alternate signs, and therefore, they lead to stable and unstable equilibrium points. In this sense, Tallarida [474] used a (7-shaped feedback curve to analyze experiments involving neurotransmitter norepinephrine systems [475]. 

Analysis on the state space proved to be very useful and demonstrated how 

As we proceed it will be seen that the most important results do not depend on a particular assumption regarding the form of the feedback function. Thus far we have not located the equilibrium points for the system under study because the function f (v) was kept general. The model we have used is applicable to both endogenous and exogenous substances. 

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Figure 11.3 State space for different initial conditions. The equilibrium point Pi ( o ) is a stable focus, P2 ( ) is an unstable saddle point, and P3 ( ) is stable.

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