Answer:
Acetylcholine receptors.
Explanation:
Acetylcholine receptors are basically membrane proteins present on the muscle cells at the synaptic end of neuromuscular junction.
A neurotransmitter known as acetylcholine binds with these acetylcholine receptors and response generated by these membrane proteins when signal transduced into muscular cell, the muscular contraction will occur and when signal ends then muscular relaxation phase started.
