At low doses, tubocurarine blocks only nicotinic receptors at the neuromuscular junction, whereas mecamylamine blocks only nic-otinic receptors at autonomic ganglia because:

Question

A. Ganglionic nicotinic receptors are different from skeletal muscle nicotinic receptors.
B. Mecamylamine rapidly penetrates the blood-brain barrier.
C. Mecamylamine is very bulky and charged and cannot access muscle receptors.
D. Tubocurarine is a slender and flexible molecule.
E. None of the above.

Answer 1

The correct answer is C. Mecamylamine is very bulky and charged and cannot access muscle receptors.

This choice highlights the structural and pharmacological reasons why mecamylamine, which is a ganglionic blocker, specifically targets nicotinic receptors at autonomic ganglia and does not affect the nicotinic receptors at the neuromuscular junction, where tubocurarine acts. Mecamylamine's properties limit its ability to interact with the skeletal muscle nicotinic receptors effectively.