Question at position 58 Which statement correctly explains the role of sympathetic nervous system input during exercise?It decreases blood circulation to prevent muscle fatigue.It increases heart rate by releasing norepinephrine and epinephrine.It slows down the heart to conserve oxygen.It releases acetylcholine to reduce energy expenditure.

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BlackTom AI · Accepted Answer

Consider the role of the sympathetic nervous system (SNS) during exercise and how it modulates cardiovascular function.
Option 1: 'It decreases blood circulation to prevent muscle fatigue.' This is incorrect because the SNS actually increases blood flow to muscles by dilating vessels in active muscles and redistributing blood, not decreasing circulation; its goal is to support performance, not limit circulation.
Option 2: 'It increases heart rate by releasing norepinephrine and epinephrine.' This statement is accurate. During exercise, the SNS stimulates the heart via norepinephrine (noradrenaline) release from sympathetic nerves and epinephrine (adrenaline) release from the adrenal medulla, which collectively raise heart rate and contractility to boost cardiac output.
Option 3: 'It slows down the heart to conserve oxygen.' This misstates the SNS’s effect; rather than slowing the heart, the SNS accelerates heart rate to meet the increased metabolic demand; slowing the heart would reduce oxygen delivery to tissues when it’s most needed.
Option 4: 'It releases acetylcholine to reduce energy expenditure.' This describes parasympathetic activity, not sympathetic. Acetylcholine release from parasympathetic nerves slows the heart and promotes rest-and-digest functions, whereas during exercise the sympathetic system is predominant to increase energy expenditure and performance.
Putting these together, the option that correctly captures the SNS’s action during exercise is the one about increasing heart rate through norepinephrine and epinephrine, while the other choices describe effects that are either opposite, incorrect, or pertain to the parasympathetic system rather than the sympathetic system.

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