Figure 2.

Multiple areas are affected in ALS. Upper motor neurons in the motor cortex have been implicated in affecting voluntary breathing. Upper airway muscles including the nares dilators, tongue, palatal elevators and vocal cord abductors become weak, leading to loss of upper airway tone, problems swallowing and difficulty clearing the airway. As phrenic motor neurons degenerate, diaphragm activity will be compromised, causing the diaphragm to atrophy and weaken. Atrophy and weakness can also occur in accessory respiratory muscles including the intercostal (both inspiratory and expiratory) muscles, rectus abdominus, external obliques, sternocleidomastoids, scalenes, trapezii, latissimus dorsi, and pectorals. Weakness in these muscles contributes to respiratory compromise and, ultimately, failure.