What is a physiological effect of stress on the nervous system?

The correct answer highlights "increased vigilance" as a physiological effect of stress on the nervous system. When an individual experiences stress, the body's "fight or flight" response is activated. This is largely driven by the sympathetic nervous system, which prepares the body to respond to perceived threats.

Increased vigilance involves heightened awareness and responsiveness to potential dangers in the environment. This physiological response prepares the individual to react quickly, enhancing survival chances during stressful situations. The release of neurotransmitters, such as norepinephrine and adrenaline, plays a significant role in this process, facilitating quicker reflexes and sharper focus.

While other options address aspects related to stress or the nervous system, they do not capture the essence of what occurs during the stress response. For instance, decreased heart rate typically represents a relaxed state rather than a stress response. Similarly, while serotonin is a neurotransmitter involved in mood regulation, its release does not significantly increase during stress; instead, it may actually be lower under stress. Finally, cognitive function may become impaired under significant stress, as attention can become narrowly focused, which might hinder overall cognitive processes rather than improve them. Thus, "increased vigilance" is the most fitting physiological effect of stress on the nervous system.