Amyotrophic lateral sclerosis (ALS) is caused by loss of motor neurons and muscle atrophy, which leads to progressive neurodegeneration. It is estimated that 12,000-15,000 people in the US are living with ALS. While the identification of therapies for ALS is an area of active research, existing treatments for ALS are ineffective. Drug screening for ALS has been traditionally low-throughput due to use of genetically engineered mouse models. Additionally, in vitro drug screening attempts have been conducted on incomplete models of the neuromuscular junction. This invention is a microfluidic device that models the human neuromuscular motor unit in 3D space, facilitating in vitro human disease modeling and higher-throughput drug screening for ALS and other motor neuron diseases.