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.
