After axonal degeneration, what happens to motor units?

After axonal degeneration, what happens to motor units?

• A. They become hyperactive
• B. They regenerate spontaneously
• C. They become denervated
• D. They increase in size

Answer: (C)

Motor units are a motor neuron together with all the muscle fibers it controls. When the axon degenerates, its connection to those muscle fibers is lost, so the fibers no longer receive neural input. Those fibers become denervated and cannot be activated by that neuron anymore. Over time, if nearby nerves sprout to reinnervate them, reinnervation can occur and motor units may change in size, but immediately after axonal degeneration the key change is denervation.

Motor units are a motor neuron together with all the muscle fibers it controls. When the axon degenerates, its connection to those muscle fibers is lost, so the fibers no longer receive neural input. Those fibers become denervated and cannot be activated by that neuron anymore. Over time, if nearby nerves sprout to reinnervate them, reinnervation can occur and motor units may change in size, but immediately after axonal degeneration the key change is denervation.