Receptors for acetylcholine are located on the

plasma membrane of the target cell

Explanation:

There are two main types of acetylcholine (ACh)receptors:

muscarinic ACh receptors (because muscarin as agonist) which are G-protein coupled receptors that initiate slow response. Mostly, they are located in the central nervous system-CNS (involved in the release of neurotransmitters), heart (control of the heart rate), smooth muscles (contraction).nicotinic ACh receptors (nicotin is agonist) which are  ligand-gated ion channels involved in the fast response. They are located at neuromuscular junctions but also in CNS (involved in synaptic transmission between two neurons).

This movement is also referred to as  glacial plucking