What happens to muscle tone when there is damage to Upper Motor Neurons?

• A. It becomes flaccid and weak
• B. It leads to hypotonia and muscle relaxation
• C. It results in spasticity and contralateral weakness
• D. It causes muscle rigidity and loss of sensation

Answer: (C)

When there is damage to Upper Motor Neurons (UMNs), the typical response in muscle tone is to become spastic. This phenomenon occurs because UMNs are primarily responsible for the modulation of muscle tone and reflexes. When these neurons are damaged, there is a loss of their inhibitory control over lower motor neurons and the muscle reflex arc, which can lead to increased excitability of the lower motor neurons.

As a result of this loss of inhibition, there is an excessive and uncontrolled contraction of muscles, leading to spasticity. This condition is characterized by an increase in muscle tone and resistance to passive movement. Furthermore, damage to UMNs can also lead to contralateral weakness because UMNs from one side of the brain control the opposite side of the body. Therefore, the changes in muscle tone and strength are directly linked to the nature of UMN damage, making spasticity and contralateral weakness the correct response.