Darrin is watching a horror movie. When the evil main character makes a surprise appearance, Darrin jumps out of his seat, his heart rate accelerates, and he screams. Which of the following pathways most directly contributes to his ability to calm down after this startle response? The reflex arc The somatic nervous system The parasympathetic nervous system The sympathetic nervous system
The Correct Answer and Explanation is:
The parasympathetic nervous system most directly contributes to Darrin’s ability to calm down after the startle response.
When Darrin jumps in surprise, his body responds with a rapid increase in heart rate, rapid breathing, and heightened alertness. This is primarily driven by the sympathetic nervous system (SNS), which is responsible for the “fight-or-flight” response. It prepares the body for immediate action by releasing stress hormones like adrenaline, which increase heart rate, dilate pupils, and inhibit digestion, among other effects.
However, once the perceived threat (in this case, the sudden appearance of the villain) is no longer present, Darrin’s body needs to return to a state of calm. This is where the parasympathetic nervous system (PNS) comes in. The PNS is often referred to as the “rest-and-digest” system, and its role is to counterbalance the actions of the sympathetic system. It promotes relaxation and restoration of normal body functions.
Specifically, the PNS slows down the heart rate, reduces blood pressure, and encourages digestion, allowing the body to recover from the heightened state of arousal. This action is mediated through the vagus nerve, which releases acetylcholine, a neurotransmitter that helps slow the heart rate and decrease the body’s overall energy expenditure.
In contrast, the somatic nervous system controls voluntary muscle movements, which wouldn’t directly help Darrin calm down. The reflex arc is responsible for automatic, rapid responses to stimuli (like jumping at a scary scene), but it doesn’t play a role in calming down after the fact. The sympathetic nervous system is primarily involved in the initial startle response, but it’s the parasympathetic system that restores balance and helps Darrin relax afterward.
