system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
When the sympathetic nervous system is activated
assistant
The correct answer is  Nerve fibers, not vascular smooth muscle, release norepinephrine. The norepinephrine from the sympathetic nerves simply diffuses from the axons and binds to specific receptors on smooth muscle cells.