What did Lou Gehrig's disease mostly affect?

Lou Gehrig's disease, medically known as amyotrophic lateral sclerosis (ALS), primarily affects the motor neurons in the brain and spinal cord. This degeneration leads to muscle weakness, loss of motor control, and eventually paralysis, as the brain's ability to initiate and control voluntary movements deteriorates. While cognitive functions are often preserved, the disease significantly impacts daily living and overall quality of life.