Final answer:
Epinephrine and norepinephrine are released by the sympathetic nervous system in response to stress.
Step-by-step explanation:
The neurotransmitters released when the sympathetic nervous system is activated by a stressor are epinephrine and norepinephrine. These neurotransmitters are released by the adrenal medulla and the nervous system respectively, and are part of the body's fight-or-flight response to stress. They increase heart rate, force of contraction, and constrict blood vessels to organs not essential for flight-or-fight responses.