"Cholinergic" refers to anything related to the neurotransmitter acetylcholine, which plays a crucial role in transmitting signals in the nervous system. Cholinergic neurons release acetylcholine to communicate with other neurons, muscles, and various organs, influencing functions such as muscle movement, heart rate, and memory. Cholinergic receptors are classified into two main types: nicotinic and muscarinic. Nicotinic receptors are found at the neuromuscular junction and in the autonomic nervous system, while muscarinic receptors are primarily located in the heart and smooth muscles. Understanding cholinergic systems is essential for studying conditions like Alzheimer's disease and myasthenia gravis.