The chemical signal used by neurons to communicate across synapses is called what?

• A. Hormone
• B. Neurotransmitter
• C. Enzyme
• D. Receptor

Answer: (B)

Neurons communicate across synapses using chemical signals called neurotransmitters. When an action potential reaches the presynaptic terminal, it triggers the release of neurotransmitters into the synaptic cleft. These chemicals diffuse across the gap and bind to receptors on the postsynaptic membrane, causing ion channels to open or signaling cascades to start, which can either excite or inhibit the next neuron. This rapid, local form of signaling is distinct from hormonal signaling, which travels through the bloodstream to distant targets. Receptors are the binding sites that detect signaling molecules, not the signals themselves, and enzymes are biological catalysts that can metabolize neurotransmitters but do not serve as the signaling message crossing the synapse.