Final answer:
If a motor neuron is permanently damaged, the innervated muscle cells will undergo atrophy and be replaced by connective and adipose tissue, leading to flaccid paralysis, characterized by a loss of muscle control and reflexes.
Step-by-step explanation:
If a motor neuron is damaged permanently, the muscle cells it innervates will atrophy or waste away. This occurs because the damaged neuron can no longer send signals to the muscle cells, leading to a loss of muscle function, decreased muscle tone, and over time muscle cell death followed by replacement with connective and adipose tissue. This condition is often referred to as flaccid paralysis and is characterized by the lack of voluntary muscle control, muscle tone, and reflexes.
In conditions such as Amyotrophic Lateral Sclerosis (ALS), where motor neurons degenerate, this process leads to the hardening of the lateral portion of the spinal cord, which impairs signal transmission to the muscles, resulting in weakness, loss of coordination, and eventually to paralysis. Such injuries to the nervous system, including spinal cord injuries, are particularly severe because most nerve tissues are not capable of regeneration. For individuals with paralysis, physical therapy and methods like electrical stimulation can sometimes be utilized to maintain muscle function and prevent complete muscle loss.