Muscarinic receptors are found mostly in autonomic ganglia. always produce an excitatory response. control sodium channels in the affected membrane. *are normally activated by acetylcholine. are blocked by norepinephrine

are normally activated by acetylcholine.

Explanation:

The cholinergic receptors bind to acetylcholine (ACh) and are of two types: nicotinic receptors and muscarinic receptors. Muscarinic receptors are present in the plasma membranes of all effectors such as smooth muscle, cardiac muscle, and glands. Activation of muscarinic receptors by acetylcholine may cause depolarization (excitation) or hyperpolarization (inhibition), depending on which particular cell has the muscarinic receptors.

For example, binding of ACh to muscarinic receptors inhibits smooth muscle sphincters in the gastrointestinal tract but binding of ACh excites muscarinic receptors in smooth muscle fibers circular muscles of the iris of the eyes.