What action do alpha motor neurons perform on muscle spindles?

What action do alpha motor neurons perform on muscle spindles?

• A. Move
• B. Sensitize spindles
• C. Relax spindles
• D. Inhibit spindles

Answer: (A)

Alpha motor neurons cause contraction of extrafusal muscle fibers, which makes the muscle shorten and move. The muscle spindle sits in the muscle, so when the surrounding muscle contracts and moves, the spindle is moved as well. The spindle’s sensitivity is adjusted mainly by gamma motor neurons, not by alpha ones, which is why actions like sensitizing, relaxing, or inhibiting the spindle aren’t the direct result of alpha motor neuron activity. In short, activating alpha motor neurons moves the muscle—and with it, the spindle—through contraction.

Alpha motor neurons cause contraction of extrafusal muscle fibers, which makes the muscle shorten and move. The muscle spindle sits in the muscle, so when the surrounding muscle contracts and moves, the spindle is moved as well. The spindle’s sensitivity is adjusted mainly by gamma motor neurons, not by alpha ones, which is why actions like sensitizing, relaxing, or inhibiting the spindle aren’t the direct result of alpha motor neuron activity. In short, activating alpha motor neurons moves the muscle—and with it, the spindle—through contraction.