Final answer:
The somatic nervous system enables voluntary movement like running from a mountain lion, while the sympathetic division of the autonomic nervous system is responsible for increased heart rate and other physiological changes during such intense activity.
Step-by-step explanation:
While running from the mountain lion that you happened to cross paths with during a hike, the somatic nervous system, a division of the peripheral nervous system that controls voluntary activities such as moving your legs, allows you to do so.
This system is distinct from another subdivision called the autonomic nervous system, which further divides into the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system is activated in response to threats and is responsible for the physiological changes experienced during exercise or when fleeing from danger. It increases heart rate, breathing rate, redirects blood flow to skeletal muscles, and induces sweating.
On the other hand, the parasympathetic nervous system often works in opposition to the sympathetic system and is involved in rest and digestion activities.