How come there are some automated body functions that we can “override” and others that we can’t?

Question

For example, we can will ourselves breathe/blink faster, or choose to hold our breath. But at the same time, we can’t will a faster or slower heart rate or digestion when it might be advantageous to do so. What is the difference in the muscles involved or brain regions associated with these automated functions?

In: Biology

Answer 1

Aren’t there monks that can slow their heart rate?