Muscle A and muscle B have the same number of fibers, but muscle A is capable of more precise control than muscle B. Which of the following is likely to be true of muscle A? (Explain your answer.)
a. It is controlled by more neurons than muscle B
b. It contains fewer motor units than muscle B
c. It is controlled by fewer neurons than muscle B
d. It has larger sarcomeres than muscle B

Verified step by step guidance

1. Understand the concept of motor units: A motor unit consists of a single motor neuron and all the muscle fibers it controls. Precision in muscle control is achieved when each motor neuron controls fewer muscle fibers, allowing finer adjustments.
2. Analyze the relationship between motor units and precision: Muscles capable of more precise control typically have more motor units, meaning more neurons control smaller groups of muscle fibers. This allows for finer control of movement.
3. Evaluate the options: Option (a) suggests muscle A is controlled by more neurons, which aligns with the idea that more motor units lead to greater precision. Option (b) suggests fewer motor units, which would reduce precision. Option (c) suggests fewer neurons, which contradicts the need for more motor units for precision. Option (d) mentions larger sarcomeres, which are unrelated to precision control.
4. Eliminate incorrect options: Based on the explanation, options (b), (c), and (d) can be ruled out because they do not support the idea of increased precision in muscle control.
5. Conclude the correct answer: The most likely explanation is that muscle A is controlled by more neurons than muscle B, as this allows for more motor units and finer control.

Key Concepts

Motor Units

A motor unit consists of a single motor neuron and all the muscle fibers it innervates. Muscles that require precise control, such as those involved in fine motor skills, typically have smaller motor units, allowing for more refined movements. In contrast, muscles that perform gross movements have larger motor units, which can control more fibers but with less precision.

Neuron Control

The number of neurons controlling a muscle affects its precision of movement. More neurons can lead to more motor units, which allows for finer control over muscle contractions. This is particularly important in muscles that perform delicate tasks, where precise adjustments are necessary for effective function.

Sarcomere Structure

Sarcomeres are the basic contractile units of muscle fibers, composed of actin and myosin filaments. While the size of sarcomeres can influence muscle contraction strength, it does not directly relate to the precision of control. Therefore, larger sarcomeres are not necessarily indicative of a muscle's ability to perform precise movements.