In the nervous system, which neurotransmitter is primarily inhibitory in the brain and spinal cord?

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

Answer: (A)

The main idea here is that inhibitory signaling in the CNS is dominated by GABA. GABA binds to its receptors on neurons in the brain and spinal cord and opens chloride channels, which drives the postsynaptic membrane toward the chloride equilibrium and hyperpolarizes the cell. That makes it harder for the neuron to reach the threshold for firing, damping neural activity.

There are two major receptor types: GABA-A, which is ionotropic and produces fast inhibition, and GABA-B, which is metabotropic and produces slower, longer-lasting inhibition by influencing potassium and calcium channels. This inhibitory action is crucial for balancing excitation and preventing overactivation that could lead to seizures.

In contrast, the other neurotransmitters have different primary roles: glutamate is the main excitatory transmitter, driving neuronal activity; norepinephrine modulates arousal and attention; acetylcholine has diverse functions and can be excitatory or modulatory depending on the receptor and context. Because of these roles, GABA is the best answer for the neurotransmitter that is primarily inhibitory in the brain and spinal cord.