Question

a single contraction-relaxation cycle in a muscle fiber produces a(n)

action potential.
motor unit.
tetanic contraction.
cramp.
twitch.

Explanation:

🆕 New Concept Discovered: Muscle Twitch Mechanics
A single, rapid contraction-relaxation cycle of a muscle fiber.

Step 1: Define a muscle twitch

A muscle twitch is the basic response of a single muscle fiber (or a motor unit) to a single action potential. It consists of three distinct phases:

1. Latent period: The delay between the stimulus and the start of the contraction.
2. Contraction phase: Muscle tension increases as cross-bridges form.
3. Relaxation phase: Muscle tension decreases as calcium is pumped back into the sarcoplasmic reticulum.

This entire single cycle of contraction and relaxation is called a twitch.

Step 2: Evaluate the other options

• action potential: This is the electrical signal traveling down the neuron or muscle membrane that triggers the contraction, not the physical contraction-relaxation cycle itself.
• motor unit: This is a structural unit consisting of a single motor neuron and all the muscle fibers it innervates.
• tetanic contraction: This is a sustained, smooth contraction that occurs when a muscle fiber is stimulated repeatedly at a high frequency, preventing it from relaxing.
• cramp: This is an involuntary, painful, and prolonged muscle contraction.

Answer:

twitch.