What accounts for the longest delay in neuronal signalling?

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Question restatement: What accounts for the longest delay in neuronal signalling?

Option a: Sodium channel opening. While opening voltage-gated sodium channels is essential for action potential initiation and rapid depolarization, this step occurs within the axon and is comparatively fast, contributing less to the overall delay than synaptic processes.

Option b: Calcium entry into the synapse. Calcium influx triggers neurotransmitter release at the presynaptic terminal, which introduces a delay due to vesicle docking and fusion. However, this event is part of the broader synaptic transmission sequence and is typically shorter than the total time required for the downstream chemical signaling chain.

Option c: Chemical transmission at the synapse. This choice points to the core sequence: neurotransmitter release, diffusion across the synaptic cleft, receptor binding, and postsynaptic response. Each of these stages unfolds over milliseconds to tens of milliseconds and collectively accounts for the most substantial portion of the delay in neuronal communication, especially compared to purely electrical processes along the axon.

Option d: Potassium entry into the cell. Potassium efflux or influx shapes the repolarization phase and resting membrane potential dynamics, but the time course of these ionic movements is generally rapid and does not introduce the longest delay when compared with the complete chemical synaptic transmission sequence.

Putting these pieces together, the longest delay in a typical neuronal signaling pathway arises from the full chemical transmission at the synapse, which encompasses vesicle release, diffusion across the synaptic cleft, and postsynaptic receptor activation, all contributing to the principal temporal bottleneck in signal propagation.

NUT1103 S2 2025 Mid-semester exam

What accounts for the longest delay in neuronal signalling?

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