Which two drugs would prevent a skeletal muscle from responding to an electrical stimulus in the presynaptic neuron? (a) I and II

Question

Certain drug acts at synapses and affects the action of neurotransmitter substances. The table shows the effects of four different drugs. 

Drug Effect 

I. Inhibits the enzyme cholinesterase. 

II. Prevents the release of acetylcholine. 

III. Competes with acetylcholine at receptor sites. 

IV. Inhibits the enzyme which destroys nor-adrenaline.

Which two drugs would prevent a skeletal muscle from responding to an electrical stimulus in the presynaptic neuron? 

(a) I and II 

(b) I and IV 

(c) II and III 

(d) II and IV

Answer 1

Correct option is (c) II and III

The drugs will only prevent the response of the muscle to an electrical stimulus if it prevents the release of acetylcholine and so inhibits the increase in membrane permeability to sodium ions, and if the drug competes with acetylcholine at the receptor sites.