Final answer:
Pupil dilation in the dark is regulated by the autonomic nervous system, specifically the sympathetic division, which allows the pupils to expand from about 3 mm to 7 mm in diameter to let in more light. The process is mediated by nerve signals from the optic nerve to the midbrain and adjustments in the ciliary ganglion. Observing pupil size in different lighting during a take-home experiment can demonstrate this response.
Step-by-step explanation:
Pupils dilating in response to darkness is a consequence of the autonomic nervous system's regulation of the pupil's size to control the amount of light entering the eye. In normal light, the pupil has a smaller diameter, often around 3 mm, to prevent excessive light from overwhelming the retina. Conversely, in low light conditions, the sympathetic nervous system takes charge, causing the pupils to dilate up to about 7 mm, allowing more light into the eye.
The process behind this involves the optic nerve sensing the reduction in light and signaling the brain's midbrain areas, specifically the pretectal nucleus and the Edinger-Westphal nucleus. This neuronal activity leads to the regulation of the ciliary ganglion, which in turn adjusts the pupil size through the action of neurotransmitters like acetylcholine and the fibers within the iris.
When conducting a take-home experiment on the pupil, one can observe this dilation first-hand by comparing pupil sizes in different lighting conditions. This dilation also indicates why wearing sunglasses without UV blockers can be hazardous. By reducing visible light, sunglasses cause the pupil to dilate, potentially allowing more harmful UV radiation to enter the eye if the sunglasses don't provide adequate UV protection.