Which of the following accounts for the largest percentage of basal metabolic rate (BMR)?

• A. Digestive system
• B. Nervous system
• C. Skeletal muscle
• D. Cardiovascular system

Answer: (B)

The choice indicating that the nervous system accounts for the largest percentage of basal metabolic rate (BMR) highlights an important aspect of energy expenditure in the body. While the nervous system does require a significant amount of energy to function, especially for maintaining resting membrane potential and supporting various neural activities, it is not the primary contributor to BMR.

In reality, skeletal muscle is the largest consumer of energy at rest, contributing the most to BMR due to its mass and activity level, even when the body is at rest. Skeletal muscle has a high metabolic rate compared to other tissues. It continually requires energy, primarily adenosine triphosphate (ATP), for processes like maintaining tone and basic cellular function.

Digestive and cardiovascular systems do utilize energy, but their contributions to BMR are not as significant as that of skeletal muscle. The digestive system processes food and absorbs nutrients, while the cardiovascular system maintains circulation, both of which are essential but represent a smaller portion of the overall energy expenditure when the body is at rest.

Thus, the understanding of the contributions to BMR illustrates that the skeletal muscle holds a pivotal role, primarily due to its overall mass and metabolic demands, exceeding other systems like the nervous system in terms of energy consumption at rest.