Which statement correctly describes neurotransmitters?

• A. Hormones
• B. Enzymes
• C. Receptors
• D. Neurotransmitters

Answer: (D)

Neurotransmitters are chemical messengers released from the presynaptic neuron into the synaptic cleft when an action potential arrives. They bind to receptors on the postsynaptic cell, triggering excitation or inhibition that propagates or moderates the neural signal. After their job is done, they’re removed from the synapse by reuptake or enzymatic breakdown to stop the signal. This makes them the actual signaling chemicals at synapses, distinct from other players.

They’re different from hormones, which travel through the bloodstream to affect distant targets. They’re different from enzymes, which are catalysts that speed up chemical reactions. And they’re different from receptors, which are the proteins on the postsynaptic membrane that respond to neurotransmitters but are not themselves the signaling molecules.