Name two major excitatory and two major inhibitory neurotransmitters in the CNS.

• A. Excitatory: dopamine and norepinephrine; Inhibitory: GABA and glycine.
• B. Excitatory: acetylcholine and dopamine; Inhibitory: serotonin and norepinephrine.
• C. Excitatory: glutamate and aspartate; Inhibitory: GABA and glycine.
• D. Excitatory: GABA and glycine; Inhibitory: glutamate and aspartate.

Answer: (C)

Glutamate and aspartate are the main excitatory transmitters in the CNS, while GABA and glycine are the main inhibitory ones.

Glutamate is the primary fast excitatory signal throughout the brain, acting on NMDA, AMPA, and kainate receptors to push neurons toward firing. It also plays a key role in synaptic plasticity, which underlies learning and memory. Aspartate is also excitatory, contributing to signaling mainly through NMDA-type receptors, though its role is typically less prominent than glutamate’s.

On the inhibitory side, GABA is the dominant inhibitory transmitter in the brain. It binds to GABA-A receptors, opening chloride channels for rapid hyperpolarization, and also to GABA-B receptors to dampen excitability more slowly via GPCR signaling. Glycine serves as the main inhibitory transmitter in the spinal cord and brainstem, acting on glycine receptors to hyperpolarize neurons.

Other neurotransmitters listed in some options, like dopamine, norepinephrine, acetylcholine, and serotonin, can modulate activity and have excitatory or inhibitory effects depending on receptor type and location, but they are not the two universal major excitatory and two universal major inhibitory transmitters in the CNS.