Answer: The principle that describes the nervous system's ability to recruit the correct muscles to perform movement is motor unit recruitment.
Step-by-step explanation:
Motor unit recruitment refers to the process by which the nervous system activates and coordinates the contraction of specific motor units, which consist of a motor neuron and the muscle fibers it innervates.
Here's how motor unit recruitment works:
1. Motor neurons: The nervous system consists of motor neurons that extend from the spinal cord to muscle fibers. Each motor neuron is responsible for controlling a group of muscle fibers, which are referred to as a motor unit.
2. Hierarchy of motor units: Motor units can be categorized based on their size and function. Small motor units contain fewer muscle fibers and are responsible for fine movements that require precise control, such as those involved in typing or playing the piano. Large motor units consist of more muscle fibers and are involved in powerful movements, such as lifting heavy objects.
3. Order of recruitment: When a movement needs to be performed, the nervous system recruits motor units in a specific order. Initially, small motor units are recruited to perform low-force, fine movements. As the intensity of the movement increases, larger motor units are recruited to generate more force.
4. All-or-none principle: Within a motor unit, all the muscle fibers contract together in response to a signal from the motor neuron. This follows the all-or-none principle, which means that once a motor unit is activated, all the muscle fibers within it contract fully.
5. Gradation of force: By recruiting motor units of different sizes, the nervous system can gradate the force output of a muscle. For example, when picking up a light object, only small motor units may be recruited. However, when lifting a heavier object, larger motor units are progressively recruited to generate more force.
In summary, motor unit recruitment is the principle that explains how the nervous system selects and activates the appropriate motor units to perform a movement. It follows a hierarchical order, where smaller motor units are recruited for fine movements, and larger motor units are recruited for more forceful movements. This principle allows for the precise control and gradation of muscle force during various activities. The specificity principle, overload principle, and neuromuscular efficiency are related concepts but do not specifically describe the nervous system's ability to recruit the correct muscles for movement.