Question

Muscle fibers involved in fine motor control are generally innervated by small motor neurons with relatively small motor units, including those that innervate single fibers. These neurons fire in response to a smaller depolarizing stimulus compared with motor neurons with larger motor units. As a result, during weak contractions, increases in muscle contraction can occur in small steps, allowing for fine motor control. This concept is called the size principle. What is the concept called?

1) Size principle
2) Motor unit principle
3) Motor control principle
4) Fine motor principle

Answer 1

The concept that allows muscle contractions to increase gradually for enhanced fine motor control, due to the progressive recruitment of motor units from smallest to largest, is known as the size principle.

Step-by-step explanation:

The concept that describes how changes in muscle contraction during weak contractions occur in small steps, which allows for refined fine motor control, is called the size principle. According to this principle, muscle fibers are innervated by different sizes of motor neurons, which correspond to the size of the motor unit. Smaller motor units, which have smaller, more excitable motor neurons, are activated first for tasks requiring fine control. When more strength is required, larger motor units with higher-threshold, bigger motor neurons are recruited progressively to generate a stronger muscle contraction. This mechanism is essential for tasks that range from picking up a feather with minimal force to lifting heavy weights by enlisting the largest motor units.