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Question Video: Stating the Effect of the Sympathetic Nervous System on the Eyes Biology

The table shows the effect of the parasympathetic and sympathetic nervous systems on some major organs and glands. What effect does the sympathetic nervous system have on the pupils?

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Video Transcript

The table provided shows the effect of the parasympathetic and sympathetic nervous systems on some major organs and glands. What effect does the sympathetic nervous system have on the pupils? (A) It constricts the pupils. (B) It dilates the pupils. (C) The pupils are not affected.

To answer this question, we must first recall what the parasympathetic and sympathetic nervous systems do and how these systems function in the body.

The sympathetic and parasympathetic nervous systems are two subdivisions of the autonomic nervous system, which is responsible for the involuntary motor functions of the body. These two subdivisions of the autonomic nervous system work in opposition to one another.

The parasympathetic nervous system is active during times of rest, relaxation, and feeding. So its responses are called the rest-and-digest responses, which support decreased alertness and wakefulness. The goal of the parasympathetic nervous system is to conserve and restore energy. So an example of these responses are slowing the heart rate, decreasing blood pressure, stimulating digestion, and promoting sleep. The processing of food and promotion of sleep are then used to build tissue and restore energy stores.

In contrast, the sympathetic nervous system takes over in times of stress and danger as the body is preparing for action. So its responses are termed the fight-or-flight responses, which support increased alertness and wakefulness. The goal of the sympathetic nervous system is to release stored energy to respond to danger or stress. An example of these actions are increased heart rate, dilated airways, and the slowing of nonessential body functions that are less important in emergencies, like digestion and urination.

So now that we know a little bit more about these systems, we can discuss how the sympathetic nervous system affects our pupils. First, we must recall that the basic function of pupils is to change the amount of light being let into the eye. Since the parasympathetic nervous system helps to conserve energy through the promotion of actions like sleep, its effect on the pupils would lead to their constriction, which would decrease the amount of light being let into the eye. Since the sympathetic nervous system response is related to increased alertness and wakefulness, its effect would increase the amount of light entering in the eye through pupil dilation. When pupils dilate, more light can enter the eye and it allows for a better response to changes in the environment. So while the parasympathetic nervous system constricts the pupil, the sympathetic nervous system dilates it.

With this information, we can complete the table and answer the question. The effect that the sympathetic nervous system has on the pupils is that it dilates the pupils.

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