This paper is an extension of the previous two papers (Mustafa et al., 2009a, b) on the modeling, simulation and analysis of bifurcation, dynamics, and chaotic characteristics of the acetylcholine (ACh) neurocycle. The effects of cholineacetyltransferase (ChAT) activity and choline recycle ratio as bifurcation parameters, on the system performance are studied through modifying the two-compartment model. It is found that as ChAT activity increases, ACh concentration in the model compartments increases continuously. The effect of choline recycle ratio shows that choline uptake represents the key role for providing choline as a substrate for ACh synthesis. It is found that the choline recycle ratio has a great influence on all state variables in both compartments. A detailed bifurcation and sensitive analyses over a wide range of ChAT activity and choline recycle ratio parameters are carried out in order to highlight the characteristics of ACh cholinergic system like non-linear dynamics and different solutions such as multiplicity of: stationery states as well as periodic and chaotic states. The relations between the results and the functions of ACh cholinergic neurons are investigated. A comparison between the results and other experimental and physiological measurements is performed. It is found that there is a good relation between cholinergic diseases such as Alzheimer's and Parkinson's diseases, and level of ACh in brains from one side and current results extracted from the disturbances in ChAT activity and choline recycle from the other side. It is found that choline recycled is the most critical factor in ACh processes in comparison with any of the following parameters: ChAT activity, as well as feed acetate and ACh concentrations. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.