Physical Therapy Assistant Practice Exam

Which neuromuscular disorder primarily affects the anterior horn cells in the spinal cord?

1. Amyotrophic lateral sclerosis

2. Spinal muscular atrophy

3. Myasthenia gravis

4. Poliomyelitis

The correct answer is: Spinal muscular atrophy

Spinal muscular atrophy primarily affects the anterior horn cells in the spinal cord, which are responsible for innervating the skeletal muscles. This disorder is characterized by the degeneration of these motor neurons, leading to muscle weakness and atrophy. In spinal muscular atrophy, the loss of motor neurons in the anterior horn results in a progressive loss of voluntary muscle function, particularly affecting proximal muscles, which often leads to significant mobility challenges. The type and severity of symptoms can vary depending on the specific genetic mutation involved and the age of onset, but the hallmark is the selective loss of anterior horn cells. This focus on the anterior horn distinguishes spinal muscular atrophy from disorders like amyotrophic lateral sclerosis, which not only affects lower motor neurons in the anterior horn but also upper motor neurons in the brain, forming a more complex pattern of neuron involvement. Myasthenia gravis is primarily a neuromuscular junction disorder, affecting communication between nerves and muscles, rather than directly damaging the anterior horn cells. Poliomyelitis, while it does impact the anterior horn cells, is not primarily referenced in the context of the question as the principal disorder compared to spinal muscular atrophy, which is more commonly associated with this specific cellular impact.