Question

A patient is seen for evaluation of severe muscle weakness and the doctor suspects myasthenia gravis. She decides to administer a drug that increases the muscle contraction force to confirm the diagnosis. Which of the following best explains why the the drug can also cause the heart rate to slow?

a. The drug decreases the activity of acetylcholinesterase.

b. The drug increases the amount of acetylcholine released by α-motoneurons.

c. The drug increases the affinity of muscarinic acetylcholine receptors to acetylcholine.

d. The drug decreases the concentration of calcium in the extracellular fluid.

Answer 1

ans: OPTION (A)

• Acetylcholine esterase (AChE) inhibitors are considered to be the basic treatment of myasthenia gravis (MG).
• Edrophonium is primarily used as a diagnostic tool.

REASON

• Acetylcholinesterase is the enzyme that is the primary member of the cholinesterase enzyme family.
• An acetylcholinesterase inhibitor (AChEI) is the inhibitor that inhibits acetylcholinesterase from breaking down acetylcholine into choline and acetate, thereby increasing both the level and duration of action of the neurotransmitter acetylcholine in the central nervous system, autonomic ganglia and neuromuscular junctions, which are rich in acetylcholine receptors.
• Acetylcholine decreases the rate of heart beating and decreases the force of its contractions, there by decrease heart rate