Where are muscarinic receptors located?

Muscarinic receptors are a type of acetylcholine receptor that are primarily found in various tissues throughout the body, playing key roles in the parasympathetic nervous system. They are located in smooth muscles, glands, and the heart, among other places. Their presence in the heart is particularly significant because stimulation of these receptors typically results in a decrease in heart rate and the modulation of various cardiac functions.

In the heart, muscarinic receptors mediate effects that counteract the sympathetic nervous system by promoting a calming response on heart rate and reducing cardiac output when activated. This is consistent with their role in promoting "rest and digest" functions as part of the autonomic nervous system.

The other tissues mentioned do have their own receptors and functions, but muscarinic receptors are distinctly noted for their role in cardiac physiology, making this location the most relevant choice.