A smooth, sustained contraction resulting from very rapid stimulation of the muscle, in which no evidence of relaxation is seen, is called a. a twitch, b. temporal summation, c. multiple motor unit summation, d. fused tetanus.

Verified step by step guidance

1. Identify the key terms in the question: 'smooth, sustained contraction', 'very rapid stimulation', and 'no evidence of relaxation'.
2. Understand that a 'twitch' is a single, brief contraction and relaxation cycle in a muscle fiber, which does not match the description of a sustained contraction.
3. Recognize that 'temporal summation' involves increased frequency of stimulation leading to stronger contractions, but it may still show some relaxation between stimuli.
4. Consider 'multiple motor unit summation', which refers to the recruitment of additional motor units to increase muscle contraction strength, but it does not specifically describe a lack of relaxation.
5. Identify 'fused tetanus' as the condition where rapid stimulation leads to a smooth, sustained contraction without any relaxation, matching the description in the question.

Key Concepts

Muscle Contraction Types

Muscle contractions can be categorized into different types, including twitch, tetanus, and summation. A twitch is a single, brief contraction of a muscle fiber, while tetanus refers to a sustained contraction resulting from rapid stimulation. Understanding these types is crucial for distinguishing between them in physiological contexts.

Fused Tetanus

Fused tetanus occurs when a muscle is stimulated at a high frequency, leading to a sustained contraction without any relaxation between stimuli. This results in a smooth and continuous contraction, which is essential for maintaining muscle tone and performing prolonged activities. It is a key concept in understanding muscle physiology and performance.

Summation

Summation refers to the process where multiple stimuli are applied to a muscle in quick succession, leading to an increase in the strength of contraction. Temporal summation involves increasing the frequency of stimulation, while multiple motor unit summation involves recruiting more muscle fibers. Both processes are vital for understanding how muscles generate force and respond to different levels of activity.