Final answer:
The pupillary reflex (A) occurs in response to a sudden increase in light intensity, causing the pupils to constrict by a parasympathetic response through the oculomotor nerve to protect the retina from excessive light.
Step-by-step explanation:
The correct answer to the question "The ____ occurs in response to a sudden increase in light intensity" is A) pupillary reflex.
The pupillary light reflex is an automatic response controlled by the autonomic nervous system. When bright light hits the retina, it triggers a signal that travels through the optic nerve as the sensory (afferent) input. This visual sensation prompts a parasympathetic response through the oculomotor nerve and the ciliary ganglion. The response activates the circular fibers of the iris to contract, which constricts the pupils and limits the amount of light entering the eye. This reflex helps protect the retina from potential damage caused by excessive light and helps to improve the sharpness of the image seen.
The sympathetic nervous system, on the other hand, is responsible for the competing dilation reflex. The pupils dilate back to their resting size when light is removed, to allow more light in under dimmer conditions. This reflex involves a sensory signal from the retina through the optic nerve, signaling to the hypothalamus and other central nervous system locations before inducing a sympathetic response to dilate the pupils.