Lower motor neuron damage presents with which of the following signs?

Lower motor neuron damage presents with which of the following signs?

• A. Hyperreflexia, spasticity
• B. Hyporeflexia, atrophy, fasciculations
• C. Brisk reflexes
• D. Clonus

Answer: (B)

Damage to the final common pathway from the spinal cord to the muscle disrupts the motor unit itself, so you lose the ability to properly activate the muscle. That leads to weakness with decreased tone and reflexes. Because the motor nerves are no longer delivering normal input, the muscles shrink over time (atrophy) and individual motor units can fire spontaneously, producing fasciculations. In this situation, reflexes are reduced or absent (hyporeflexia/areflexia) because the reflex arc requires intact lower motor neurons. This pattern contrasts with upper motor neuron lesions, where loss of inhibitory control from the brain increases muscle tone and reflex activity, causing spasticity, brisk reflexes, and clonus. So the combination of hyporeflexia, atrophy, and fasciculations best reflects lower motor neuron damage.

Damage to the final common pathway from the spinal cord to the muscle disrupts the motor unit itself, so you lose the ability to properly activate the muscle. That leads to weakness with decreased tone and reflexes. Because the motor nerves are no longer delivering normal input, the muscles shrink over time (atrophy) and individual motor units can fire spontaneously, producing fasciculations. In this situation, reflexes are reduced or absent (hyporeflexia/areflexia) because the reflex arc requires intact lower motor neurons.

This pattern contrasts with upper motor neuron lesions, where loss of inhibitory control from the brain increases muscle tone and reflex activity, causing spasticity, brisk reflexes, and clonus. So the combination of hyporeflexia, atrophy, and fasciculations best reflects lower motor neuron damage.