Sympathetic nerves are part of the autonomic nervous system, which controls involuntary bodily functions. They are responsible for the body's "fight or flight" response, preparing it to react to stress or danger. When activated, sympathetic nerves increase heart rate, dilate airways, and redirect blood flow to essential muscles. These nerves originate in the spinal cord and extend to various organs throughout the body. They release neurotransmitters like norepinephrine, which help transmit signals that trigger physiological changes. This system works alongside the parasympathetic nervous system, which promotes relaxation and recovery after stress has passed.