问题
单项选择题
The nurse is teaching a client recently diagnosed with myasthenia gravis. The nurse should teach the client that myasthenia gravis is caused by（）
A. genetic dysfunction.
B. upper and lower motor neuron lesions.
C. decreased conduction of impulses in an upper motor neuron lesion.
D. a lower motor neuron lesion.
答案
参考答案：D
解析：
Myasthenia gravis is characterized by a weakness of muscles, especially in the face and throat, caused by a lower neuron lesion at the myoneural junction. It isn’t a genetic disorder. A combined upper and lower neuron lesion generally occurs as a result of spinal injuries. A lesion involving cranial nerves and their axons in the spinal cord would cause decreased conduction of impulses at an upper motor neuron.