What is carried across the synapse to convey signal to the next neuron?

• A. Electrical signal
• B. Chemical message
• C. Nerve impulse
• D. Synaptic current

Answer: (B)

Across the synapse, the signal is carried by a chemical message. When an action potential arrives at the presynaptic terminal, neurotransmitters are released into the synaptic cleft and diffuse across to bind receptors on the postsynaptic neuron. This chemical binding alters the postsynaptic membrane potential, either exciting or inhibiting it, and can trigger a new action potential if the signal reaches threshold. This is the hallmark of chemical synapses—the signal is the neurotransmitter itself. The other terms describe processes inside a neuron or the resulting electrical activity, not the messenger that actually crosses the gap.