The autonomic nervous system controls all of the following functions, EXCEPT?

• A. Digestion
• B. Breathing
• C. Breath holding
• D. Vessel dilation

Answer: (C)

The autonomic nervous system (ANS) regulates involuntary physiological functions in the body, including the control of digestion, blood vessel dilation, and other automatic processes.

Digestion is primarily controlled by the parasympathetic nervous system, which stimulates digestive activity, while vessel dilation is also a function of the ANS, specifically through the sympathetic division that manages blood vessel responses during stress and activity.

Breathing, although it can be influenced by both voluntary and involuntary control, is largely regulated by the autonomic nervous system. The respiratory rhythm is controlled by the brainstem, showing how this function operates automatically in the background.

Breath holding, however, incorporates voluntary control, allowing a person to consciously decide to stop breathing for a period of time. This action requires conscious effort and is not regulated by the autonomic nervous system, distinguishing it from the other functions regulated by this system. Therefore, breath holding is the correct answer as it does not fall under the direct control of the autonomic nervous system.