Which of the following serves as an effector, or as part of an effector, that functions in a negative feedback system?
A. Muscarinic Acetylcholine Receptors (mAChRs) in the SA node cells of the heart.
B. Nicotinic Acetylcholine Receptors (nAChRs) in skeletal muscle fibers located in the alveoli of the lung.
C. Glycogen Receptors in the plasma membranes of liver cells.