The two main types of acetylcholine receptors (AChRs) are nicotinic and muscarinic: 

    Nicotinic AChRs
    These receptors are ion channels that allow sodium, calcium, and potassium to pass through. They are activated by nicotine and function in the central nervous system and at the neuromuscular junction. 

Muscarinic AChRs
These receptors are G-protein coupled receptors (GPCRs) that mediate a slower metabolic response. They are activated by muscarine and function in both the central and peripheral nervous systems. There are five types of muscarinic receptors: M1, M2, M3, M4, and M5. 

Acetylcholine is a neurotransmitter that functions in the central, somatic, and autonomic nervous systems. It is released at the neuromuscular junction to activate muscles.