Which neurotransmitter is considered excitatory?

• A. GABA
• B. Serotonin
• C. Glutamate
• D. Acetylcholine

Answer: (C)

Glutamate is the primary excitatory neurotransmitter in the central nervous system. When it is released, it binds to ionotropic receptors like NMDA, AMPA, and kainate, opening cation channels that let in positive ions (Na+ and sometimes Ca2+). This influx depolarizes the postsynaptic neuron, making it more likely to fire an action potential. GABA, by contrast, is the main inhibitory transmitter, promoting hyperpolarization through chloride or potassium conductance. Serotonin can have excitatory or inhibitory effects depending on the receptor subtype, so it’s not universally excitatory. Acetylcholine is excitatory at the neuromuscular junction, but in the brain its effects vary with receptor type and location. Thus, glutamate is the neurotransmitter most consistently categorized as excitatory.