Tip

Fasciculations are caused by the spontaneous discharges produced by the damaged lower motor neurons.

Tip

In UMN lesions

• Lower extremity: muscle spasticity is more increased in extensor muscles.
  • When this inhibitory control is lost or reduced due to an UMN lesion, the result is an increase in muscle tone and spasticity, more so in muscles with anti-gravity functions such as the extensors in the legs.
• Upper Extremities (e.g., Arms): flexor muscles tend to exhibit increased tone and spasticity in UMN lesions
  • This is related to the natural posture and use of these limbs, where flexion is a more dominant and protective posture.
• Also see Extrapyramidal tracts