A hiker is on a trail and a giant grizzly bear steps out of the forest. His heart immediately begins beating faster. What is the mechanism causing this response? Describe the pathway.
a) Sympathetic nervous system; Release of epinephrine → Increased heart rate
b) Parasympathetic nervous system; Release of acetylcholine → Decreased heart rate
c) Endocrine system; Release of insulin → Increased heart rate
d) Circulatory system; Release of dopamine → Decreased heart rate
