Action potentials generated by NMES are identical to those produced volitionally, and the path from AP to contraction is:

Action potentials generated by NMES are identical to those produced volitionally, and the path from AP to contraction is:

• A. Identical; the same path
• B. Identical; different path
• C. Different; same path
• D. Different; different path

Answer: (B)

The key idea is how NMES alters which muscle fibers are activated and the route the signal takes to produce contraction, even though the electrical signal itself is the same once it starts. Action potentials generated by NMES are the same electrical signal as those produced during voluntary control. Once a motor neuron fires, the downstream steps—acetylcholine release at the neuromuscular junction, the muscle fiber’s end-plate potential, the muscle fiber action potential, calcium release, and cross-bridge cycling leading to contraction—proceed in the same way as with voluntary activation. What differs is how the AP is generated and which motor units are recruited. In voluntary movement, the brain signals the spinal cord and motor neurons in a coordinated, size-ordered fashion, so smaller, fatigue-resistant fibers tend to be activated first, giving smooth, graded force. In NMES, the external electrical stimulus tends to depolarize multiple fibers more indiscriminately and can recruit larger-diameter fibers more readily, often in a more synchronous fashion. That means the overall path from AP to contraction—while sharing the same cellular machinery—follows a different recruitment pattern, making the path to contraction effectively different.

The key idea is how NMES alters which muscle fibers are activated and the route the signal takes to produce contraction, even though the electrical signal itself is the same once it starts.

Action potentials generated by NMES are the same electrical signal as those produced during voluntary control. Once a motor neuron fires, the downstream steps—acetylcholine release at the neuromuscular junction, the muscle fiber’s end-plate potential, the muscle fiber action potential, calcium release, and cross-bridge cycling leading to contraction—proceed in the same way as with voluntary activation.

What differs is how the AP is generated and which motor units are recruited. In voluntary movement, the brain signals the spinal cord and motor neurons in a coordinated, size-ordered fashion, so smaller, fatigue-resistant fibers tend to be activated first, giving smooth, graded force. In NMES, the external electrical stimulus tends to depolarize multiple fibers more indiscriminately and can recruit larger-diameter fibers more readily, often in a more synchronous fashion. That means the overall path from AP to contraction—while sharing the same cellular machinery—follows a different recruitment pattern, making the path to contraction effectively different.