Which statement correctly describes the relationship between glutamate and GABA as described?

• A. Glutamate is excitatory; GABA is inhibitory
• B. Glutamate is inhibitory; GABA is excitatory
• C. Glutamate and GABA are both inhibitory
• D. Glutamate and GABA are both excitatory

Answer: (A)

Neurotransmitters can either increase or decrease neuronal firing, and in the brain glutamate is the primary excitatory transmitter while GABA is the primary inhibitory one. Glutamate activates NMDA and AMPA receptors, letting positive ions into the neuron and causing depolarization that promotes action potentials. GABA, especially through GABA-A receptors, opens chloride channels, leading to hyperpolarization and reduced excitability; GABA-B provides slower inhibition via potassium channels and other pathways. In the mature CNS, this push-pull balance shapes synaptic signaling and prevents overexcitation. (Note: GABA can be excitatory in very early development due to chloride gradients, but under normal adult conditions it is inhibitory.) Therefore, the statement that describes their relationship is that glutamate is excitatory and GABA is inhibitory.