What is the role of neurotransmitters in synaptic transmission?

• A. They insulate axons.
• B. They are chemical messengers released from vesicles that bind to receptors on the postsynaptic cell.
• C. They create action potentials.
• D. They degrade the extracellular matrix.

Answer: (B)

Neurotransmitters mediate synaptic transmission by acting as chemical messengers released from vesicles in the presynaptic terminal. When an action potential arrives, voltage-gated calcium channels open, calcium enters, and this triggers vesicle fusion and release of neurotransmitters into the synaptic cleft. These chemicals then bind to specific receptors on the postsynaptic membrane, either directly opening ion channels or triggering signaling cascades that alter the postsynaptic cell’s membrane potential. The resulting postsynaptic potential can be excitatory or inhibitory, influencing whether the next neuron fires. Termination of signaling occurs through reuptake, enzymatic degradation, or diffusion away from the synapse. This mechanism distinguishes neurotransmitters from other roles: they don’t insulate axons, they don’t directly create action potentials, and they don’t degrade the extracellular matrix.