A lower motor neuron lesion results in which outcome?

A lower motor neuron lesion results in which outcome?

• A. Paresis
• B. No motor innervation (paralysis)
• C. Hyperreflexia
• D. Spasticity

Answer: (B)

The key idea is that a lower motor neuron lesion cuts off the final signal pathway to the muscle. When the motor nerve input is lost, the muscle can no longer receive commands to contract, which results in paralysis. If the damage is complete, there is no motor innervation to the muscle, so it cannot move at all. Paresis means partial weakness and can occur if some motor units are spared. Hyperreflexia and spasticity are signs of upper motor neuron problems, where the control from the brain is disrupted but the peripheral nerves to muscles are intact. In LMN lesions, reflexes are typically reduced or absent, not increased, and the muscles tend to be flaccid rather than stiff.

The key idea is that a lower motor neuron lesion cuts off the final signal pathway to the muscle. When the motor nerve input is lost, the muscle can no longer receive commands to contract, which results in paralysis. If the damage is complete, there is no motor innervation to the muscle, so it cannot move at all.

Paresis means partial weakness and can occur if some motor units are spared. Hyperreflexia and spasticity are signs of upper motor neuron problems, where the control from the brain is disrupted but the peripheral nerves to muscles are intact. In LMN lesions, reflexes are typically reduced or absent, not increased, and the muscles tend to be flaccid rather than stiff.