A)In this case, we are talking of nicotinic and muscarinic receptors, in the first case the nicotinic is called like that because nicotine can activate them, meanwhile the second is not, so in the table type one would be nicotinic meanwhile type two would be muscarinic. So nicotinic receptors are ligand-activated receptors, they possess hetero-oligomers of five subunits each with four transmembrane domains, meanwhile the muscarinic are coupled to a G protein, consist of individual proteins with seven transmembrane domains.
Nicotinic receptors allow the entrance of NA+ ions or the exit of K+, In some other cases allow the pass of Ca+, depolarizing the cell and generating a postsynaptic potential. Meanwhile, the muscarinic receptors mediate the subsequent hyperpolarization (recovery of the neuron after depolarization) and a type of depolarization (slow polarization).
B)Actilcholinesterase hydrolyzes the acetylcholine and that way ends the action of the neurotransmitter released in the synaptic cleft, if this neurotransmitter is not eliminated the ionic channels mediated by the receptors would not open again, as long as the acetylcholine is still detected once depolarization occurred the channel will not open, so muscular contraction cannot happen normally if acetylcholinesterase is inhibited.