Which of the following statements about the autonomic nervous system is not true?
a. it regulates the size of the pupilsb. all of the fibers are afferent fibersc. it consists of two subdivisionsd. it is an involuntary system

The statement B that says ''All of the fibers are afferent fibers'' is not true.

Explanation:

The autonomic or vegetative nervous system (ANS), also called neurovegetative or involuntary, is the part of the nervous system that is responsible for innervating the structures or organs related to the internal involuntary activities necessary for the functioning of the organism, such as the heart, the pupils , the glands among others.

It is considered mostly as an efferent system. Its efferent pathways are formed by two types of neurons, which are the preganglionic and postganglionic, and the synapse between these fibers, forms the autonomous ganglia. Afferent impulses range from visceral receptors, chemoreceptors, osmoreceptors and baroreceptors to the central nervous system.

Anatomically, it is divided into two autonomous nervous systems: the sympathetic and the parasympathetic. The functions of both are antagonistic, thus achieving a functional balance that tends to maintain body homeostasis. These divisions originate from the central nervous system and represent the efferent pathway through which it communicates with visceral effectors. The sympathetic nervous system increases energy expenditure against adverse conditions, dilates the pupil. The parasympathetic nervous system, prevents excessive energy expenditure, contracts the pupil.