Acetylcholine is a chemical in the brain that acts as a neurotransmitter. Acetylcholine is one of many neurotransmitters in the autonomic nervous system and the only neurotransmitter used in the motor division of the somatic nervous system, sensory neurons use glutamate and various peptides at their synapses. Acetylcholine is also the principal neurotransmitter in all autonomic ganglia. Acetylcholine also behaves as an excitatory neurotransmitter at neuromuscular junctions. In the peripheral nervous system, acetylcholine activates muscles, and is a major neurotransmitter in the autonomic nervous system.