Question Video: Defining the Functions of the Autonomic Nervous System Biology

Video Transcript

Consider the following activities and processes. (1) Dilation and constriction of pupils, (2) kicking a ball, (3) breathing, (4) digestion, (5) scratching an ear. Which of the following choices shows the activities or processes controlled by the autonomic nervous system? Option (A) (2), (3), and (4); option (B) (1), (3), and (4); option (C) (4) only; option (D) (3) only; or option (E) (2) and (5).

To answer this question, we need to understand the role of the autonomic nervous system. So, let’s start by summarizing the structure and function of the human nervous system and its components. The human nervous system can be divided into two parts: the central nervous system, which is made up of the brain and the spinal cord and can be abbreviated to CNS, and the peripheral nervous system, which is made up of all the nerves which extend out from the CNS into the limbs and other organs. The peripheral nervous system can be abbreviated to PNS.

The peripheral nervous system is made up of two types of neurons: motor neurons and sensory neurons. Sensory neurons collect information, such as a change in temperature, from inside our bodies and from our external environment. They transfer this information to the CNS, where it is integrated and processed. The motor division of the PNS carries impulses from the brain to muscles, glands, or organs. These can then carry out an appropriate response, such as turning a tap to reduce the temperature of hot water.

But not all actions controlled by the motor division of the PNS are voluntary. To help explain this, we can divide the motor division of the PNS into two systems: the somatic nervous system and the autonomic nervous system. The somatic nervous system controls skeletal muscle, that is, voluntary muscle. For example, if you were to move your arms to catch a ball, that would be controlled by the somatic nervous system. The autonomic nervous system controls involuntary muscles or smooth muscle. These are found within the walls of organs and other structures, for example, the walls of the blood vessels.

You cannot control whether your blood vessels dilate or constrict. We’re unable to make a decision about this. It just happens. Similarly, we are unable to contract smooth muscle in our intestinal wall to move a bolus of food along. It just happens. So, the autonomic nervous system is in control of the involuntary actions that keep us alive.

Let’s revisit our question and decide whether the activities and processes we’re asked to consider are controlled by the autonomic nervous system. That is, do we make a decision or are they involuntary actions? Our first process, dilation and constriction of pupils, is an involuntary action. We can’t decide whether we want to dilate our pupils or not. Therefore, it is controlled by the autonomic nervous system. Our second activity, kicking a ball, is a voluntary process. Our third process, breathing, is involuntary and controlled by the autonomic nervous system. If it wasn’t, we’d stop breathing whenever we fell asleep. Our fourth process, digestion, is involuntary and so controlled by the autonomic nervous system. And our final activity, scratching an ear, is a voluntary process controlled by the somatic nervous system and not the autonomic nervous system.

We now have enough information to answer our question. Which of the following choices shows the activities or processes controlled by the autonomic nervous system? We have ticked (1), (3), and (4), so the correct answer is option (B) (1), (3), and (4).