What is a sprain?

$A:$ Myasthenia gravis is a protozoan caused disorder.
$B:$ It is affecting the neuromuscular junction leading to fatigue,weakening and paralysis of skeletal muscle.

Which of the following is incorrect regarding osteoporosis?

Which of the following is an incorrect statement about myasthenia gravis?
$(I)$ It is not an autoimmune disorder.
$(II)$ It affects the neuromuscular junction.
$(III)$ It occurs due to low $Ca^{++}$ in body fluid.
$(IV)$ Paralysis of skeletal muscle is a symptom of myasthenia gravis.

Osteoporosis,an age-related disease of the skeletal system,may occur due to:

Which sentence is true for the disease Tetany?