Neuromuscular Transmission. Myasthenia Gravis

Myasthenia Gravis is a group of disorders characterized by muscle fatigue and weakness that progressively worsens s the muscle is used. It affects about one out of every 7500 Americans, occurring more often in women than men. The most common cause is the destruction of nicotinic Ach receptor proteins of the motor end plate, mediated by antibodies of a person’s own immune system.

The release of Ach from the nerve terminals is normal, but the magnitude of the end-plate potential is markedly reduced because of the decreased availability of receptors. Even in normal muscle, the amount of Ach released with each action potential decreases with repetitive activity, and thus the magnitude of the resulting EPP falls.

In normal muscle, however, the EPP remains above the threshold necessary to initiate a muscle action potential. In contrast, after a few motor nerve impulses in a myastenia gravis patient, the magnitude of EPP falls below the threshold for initiating a muscle action potential.

A number of approaches are currently used to treat the disease. One is to administer acetylcholinesterase inhibitors, such as neostigmine.

1. Knowing the structure of neuromuscular junction, explain the mechanism of action and effect of the use of neostigmine.

2. Compare mystenia gravis as neuromuscular disorder to Duchenne muscular dystrophy. What is a mechanism of abnormal muscle function in children suffering from Duchenne muscular dystrophy?

3. Why is Duchenne muscular dystrophy called sex-linked recessive disorder?

4. How can Duchenne muscular dystrophy be treated?