Final answer:
The autonomic nervous system is responsible for responses such as pupil dilation, increased heart rate, and increased respiration when the body reacts to a perceived threat.
Step-by-step explanation:
The autonomic nervous system is responsible for responses such as pupil dilation, increased heart rate, and increased respiration when your body reacts to a perceived threat. It is activated in situations where the body needs to prepare for a fight-or-flight response. The autonomic nervous system is part of the peripheral nervous system, which also includes the sensory-somatic nervous system.