When you see someone you have a crush on and your heart pounds, your hands get sweaty, and your cheeks feel hot, your is/are active.
When you see someone you have a crush on and your heart pounds, your hands get sweaty, and your cheeks feel hot, your autonomic nervous system is/are active
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autonomic nervous system
The autonomic nervous system regulates subconscious functions such as blood pressure, heart rate, intestinal motility and pupillary diameter. It is controlled by spinal nerves, brainstem and hypothalamus and operates through the reflex. The autonomic nervous system is responsible for the sensations you have when you see the person you are in love with, your heart beats fast, your hands get sweaty and your cheeks get hot.