ALS is a combined UMN (upper motor neuron) and LMN (lower motor neuron) degenerative disease. With UMN lesions you have spastic paralysis due to loss of regulation and control over motor neurons, and with LMN lesions there is direct damage to motoneurons in the spinal cord leading to loss of function of the muscles innervated by those LMNs. Hope this helps. Cheers.