Final answer:
The Edinger-Westphal nucleus mediates pupillary constriction and accommodation by providing parasympathetic innervation to the pupil's sphincter and ciliary muscles, aiding in light regulation and lens focusing.
Step-by-step explanation:
The Edinger-Westphal nucleus is the location of parasympathetic neurons that play a crucial role in controlling the size of the pupil and the focusing power of the lens, known as accommodation. Specifically, the Edinger-Westphal nucleus mediates pupillary constriction and accommodation by providing parasympathetic innervation to the pupillary sphincter and ciliary muscles. This action helps regulate the amount of light entering the eye and focuses on objects at varying distances. The nucleus is situated in the midbrain and forms part of the oculomotor complex. It is involved in the reflex arc as the efferent branch, affecting target tissues through neurotransmitters such as acetylcholine.
During the pupillary light response, light entering the eye triggers a response in which neurons from the Edinger-Westphal nucleus generate action potentials through the oculomotor nerves, causing both pupils to constrict to control light entry. Neurons in this nucleus give rise to preganglionic parasympathetic fibers that project through the oculomotor nerve to the ciliary ganglion located in the posterior orbit. Postganglionic parasympathetic fibers then release acetylcholine onto iris muscles, resulting in pupil constriction. In contrast, the sympathetic nervous system dilates the pupil in low light conditions.
Therefore, the correct function of the Edinger-Westphal nucleus is to mediate pupillary constriction and accommodation.