Give an example of autonomous nervous system

Give an example of autonomous nervous system.
A. Certain involuntary functions (without our knowledge) are controlled by autonomous nervous system takes place in our body. A very evident observation is the reduction and expansion of the pupil of our eye.
When we enter a dark room, we cannot see anything immediately. Slowly we are able to see the things around us in the room. This is because of increase in diameter of pupil, which allows more light in.
When we come out of the dark room into broad day light, the diameter of the pupil decreases allowing less light to enter into the eyes.
Both these functions are under the influence of the autonomous nervous system.