Final answer:
A decrease in heart rate is NOT an effect of the sympathetic nervous system; instead, the sympathetic nervous system increases heart rate as part of its fight-or-flight response.
Step-by-step explanation:
The sympathetic nervous system is responsible for the "fight-or-flight" response, which prepares the body to respond to perceived threats. When this system is activated, several physiological changes occur, including: pupil dilation, increased heart rate, the mobilization of energy reserves, and an elevation of muscle tone.
Given the options provided:
a) an increase in mental alertness
b) a decrease in heart rate
c) mobilization of energy reserves
d) elevation of muscle tone
The answer to the question 'Which of the following is NOT an effect of the sympathetic nervous system?' is b) a decrease in heart rate. This is because the sympathetic nervous system typically increases the heart rate, not decreases it. Decreased heart rate is an effect of the parasympathetic nervous system, which counterbalances the sympathetic system and is associated with 'rest-and-digest' functions.