Neurotransmitter function lies at the heart of how neurons communicate. When a neuron fires, it releases chemical messengers into the synapse, which diffuse across the gap and bind to receptors on the neighboring cell. The resulting signals shape the recipient neuron's electrical state, influencing whether it will fire again. The timing, quantity, and clearance of these transmitters determine the strength and duration of brain signals, forming the foundation for thoughts, feelings, and actions. Neurotransmitter function spans a diverse family of chemicals. Small-molecule transmitters such as glutamate, GABA, acetylcholine, and the monoamines—dopamine, serotonin, and norepinephrine—play central roles, while neuropeptides provide modulatory effects over longer timescales. Receptors come in two broad classes: ionotropic receptors that produce fast, direct changes in ion flow, and metabotropic receptors that initiate signaling cascades inside the cell. The same transmitter can have different effects across brain regions, depending on receptor type and cellular context, illustrating the nuanced, location-dependent nature of neurotransmitter function. In the circuits underlying mood, memory, and movement, neurotransmitter function coordinates a spectrum of neural activity. Dopamine supports reward processing and movement through pathways linking the basal ganglia with the cortex. Serotonin and norepinephrine modulate arousal, mood, and attention, influencing how information is prioritized and perceived. Acetylcholine contributes to learning and focus in hippocampal and cortical networks, while glutamate and GABA provide the rapid excitatory and inhibitory balance that enables the formation of memories and the precise initiation of actions. Through these interactions, neurotransmitter function helps orchestrate the dynamic interplay among brain regions that supports these fundamental capabilities. Exploring neurotransmitter function involves tracing the lifecycle of transmitters—from synthesis and vesicular storage to release, receptor binding, and clearance from the synapse. Techniques in electrophysiology, imaging, and molecular biology illuminate receptor types, signaling pathways, and the modular architecture of neural networks. By mapping these mechanisms, researchers build a framework for understanding how shifts in signaling can reshape circuit dynamics, offering deep insight into the science of brain signals and the diverse phenomena that emerge from them.
