'Paraplegia' refers to the paralysis of

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

Choose the correct sentence for osteoporosis.

Select the correct statement with respect to disorders of muscles in humans.

Assertion : Arthritis or inflammation of a joint makes the joint painful.
Reason : Some toxic substances are deposited at the joint.

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.