Which of the following would slow down the breathing rate?

The correct answer is based on the role of the autonomic nervous system, specifically the parasympathetic branch, in regulating involuntary bodily functions. The parasympathetic system is often described as the "rest and digest" system; it promotes relaxation and conservation of energy, which includes slowing down the heart rate and breathing.

When the parasympathetic nervous system is activated, it stimulates the diaphragm and other respiratory muscles to reduce the rate of breathing, encouraging a calm state. This is particularly important during times of rest or following stressful situations when the body needs to return to homeostasis.

In contrast, the sympathetic nervous system, which is associated with the "fight or flight" response, typically increases heart and breathing rates in preparation for physical activity or stress. The somatic nervous system, on the other hand, primarily controls voluntary movements and does not directly influence the breathing rate in the same way.

Thus, the activation of the parasympathetic action of the autonomic nervous system is what would effectively slow down the breathing rate, leading to a more relaxed state in the body.