Increased firing of impulses by the sympathetic nervous system would cause:

 functions to regulate the body's unconscious actions.primary process is to stimulate the body's fight-or-flight response. It is, however, constantly active at a basic level to maintain homeostasis.[3] The sympathetic nervous system is described as being complementary to the parasympathetic nervous system which stimulates the body to "feed and breed" and to (then) "rest-and-digest".

Would cause heart to speed up or shut down for a little while

The right answer is c.sandstone.