What happens to muscle fibers during the "all or none" principle?

The "all or none" principle refers to the way muscle fibers respond to stimulation from nerve impulses. When a motor neuron sends a signal to a muscle fiber, that fiber either contracts fully or does not contract at all. This means that once the threshold of stimulation is reached, it causes the muscle fiber to reach its maximum contraction level. This principle ensures that muscle contractions are efficient and uniform across the fibers that are activated by a single motor neuron.

In practical terms, if the stimulus does not reach the necessary threshold, the muscle fiber will remain relaxed. Conversely, if the stimulus is strong enough to meet the threshold, then the muscle fiber will engage completely and exhibit maximal force. This mechanism is crucial for coordinated movement and strength in muscles, as it allows for precise control over contraction levels in response to varying demands.