Thiamine (vitamin b1) deficiency diseases have a lower prevalence now than in the past. however, they are seen as beriberi in some developing regions and in regions of crisis, and as wernicke–korsakoff syndrome in some alcoholics. one type of beriberi causes neurological symptoms such as weakness, fatigue, and loss of sensation.

The correct answer is ''loss of acetylcholine receptors in the end-plate membrane.''

Explanation:

Myasthenia gravis represents a human autoimmune disease. The neuromuscular junction abnormalities that occur in this disease are due to antibody-mediated processes. A reduction in the number of functional acetylcholine receptors on the postsynaptic membrane was established to contribute to the physiological abnormalities of myasthenia gravis. The reduction in receptors is due to immunological alterations directed against the acetylcholine receptor. Normally, when acetylcholine binds to its receptor, it opens allowing the rapid entry of cations, especially sodium. With this, the depolarization of the postsynaptic region of the muscle fiber occurs. Although acetylcholine is normally released in myasthenia gravis, it is not capable of causing an action potential in the muscle sufficient to initiate or weaken contraction. In patients with myasthenia gravis, failure to activate muscles is responsible for myasthenic fatigue. Most patients have elevated serum titers of antireceptor antibodies, which in turn accelerate receptor degradation.