Question

nicotinic receptors are ______ and muscarinic receptors are ______.

o always excitatory; always inhibitory
o excitatory or inhibitory; excitatory or inhibitory
o either excitatory or inhibitory; always excitatory
o always excitatory; either excitatory or inhibitory
o always inhibitory; always excitatory

Explanation:

Nicotinic receptors are ligand - gated ion channels. When acetylcholine binds to nicotinic receptors, it causes the opening of ion channels (usually sodium channels), leading to depolarization and excitation. So nicotinic receptors are always excitatory. Muscarinic receptors are G - protein coupled receptors. Depending on the type of G - protein (e.g., Gq, Gi/Go) and the target cell, muscarinic receptor activation can lead to either excitation (e.g., in smooth muscle cells via Gq - mediated IP3/DAG pathway causing contraction) or inhibition (e.g., in cardiac cells via Gi - mediated decrease in cAMP and opening of potassium channels causing hyperpolarization).

Answer:

always excitatory; either excitatory or inhibitory