ALS (Amyotrophic Lateral Sclerosis) is a progressive neurodegenerative disease that affects motor neurons in the brain and spinal cord, which are responsible for controlling voluntary muscle movements such as walking, speaking, chewing, and breathing

. As these motor neurons degenerate and die, they stop sending signals to muscles, causing muscle weakness, twitching, wasting (atrophy), and eventually loss of voluntary muscle control

. ALS typically begins with muscle weakness or stiffness, often starting in the arms or legs (limb-onset ALS) or in the muscles involved in speech and swallowing (bulbar-onset ALS)

. Symptoms progressively worsen over time, leading to difficulties in movement, speaking, swallowing, and breathing. Despite these severe physical impairments, ALS usually does not affect a person's intelligence, sensory functions (such as sight or hearing), or mental faculties

. The cause of ALS is mostly unknown, with about 85% of cases being sporadic and about 15% inherited genetically

. There is currently no cure for ALS, and treatment focuses on managing symptoms and improving quality of life

. In summary, ALS is a fatal motor neuron disease characterized by progressive muscle weakness and loss of voluntary motor control due to the degeneration of nerve cells in the brain and spinal cord