Question

Which of the following muscles would have motor units with the lowest innervation ratio? a. leg muscles b. arm muscles c. muscles that move the fingers d. muscles of the trunk

Short answer

c. Muscles that move the fingers have the lowest innervation ratio.

Step-by-step solution

Understand Innervation Ratio

Innervation ratio is the ratio of the number of muscle fibers to the number of motor neurons that control those fibers. A lower innervation ratio indicates that there are a fewer number of muscle fibers per motor neuron, allowing for more precision and control in movements. Step 2: Ranking Muscle Groups by Innervation Ratio

Ranking Muscle Groups by Innervation Ratio

Since the question asks us about the muscle group with the lowest innervation ratio, we need to rank the given muscle groups (leg, arm, finger, and trunk) in terms of their innervation ratios. Generally, muscles with more complex functions and more precise movements require a lower innervation ratio. Let's rank the muscle groups: 1. Muscles that move the fingers (high precision required for fine motor skills) 2. Arm muscles (also used for fine movements but not as precise as finger movements) 3. Leg muscles (less precision needed for supporting the body and walking) 4. Muscles of the trunk (mainly used for posture and stabilizing the body, requiring minimal precision) Step 3: Determine the Muscle Group with the Lowest Innervation Ratio

Determine the Muscle Group with the Lowest Innervation Ratio

From the ranking above, we can see that the muscle group with the lowest innervation ratio is the muscles that move the fingers, since they require the highest level of precision and control for fine motor skills. Answer: c. Muscles that move the fingers have the lowest innervation ratio.