What accounts for the longest delay in neuronal signalling?

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BlackTom AI · Accepted Answer

The question asks which factor accounts for the longest delay in neuronal signalling.
Option a: Calcium entry into the synapse. While calcium entry is crucial for triggering vesicle fusion, the actual entry of Ca2+ through voltage-gated calcium channels is a relatively rapid process and does not by itself constitute the longest delay in transmission. It initiates the sequence, but the timing bottleneck lies downstream.
Option b: Potassium entry into the cell. Potassium movements largely contribute to repolarization and membrane potential dynamics, which are fast electrical events. They do not create the maximum pause in signalling compared to the synaptic transmission steps.
Option c: Sodium channel opening. Opening of sodium channels leads to rapid depolarization and action potential propagation along the axon. This is an electrical process with milliseconds or less of delay, not the chief source of delay in transmission.
Option d: Chemical transmission at the synapse. This option refers to the sequence after the action potential reaches the presynaptic terminal: vesicle docking and fusion, neurotransmitter release into the synaptic cleft, diffusion across the cleft, receptor binding on the postsynaptic membrane, and downstream signaling. Each of these stages adds time, and together they produce the characteristic synaptic delay that is typically longer than the purely electrical steps. This makes chemical synaptic transmission the main contributor to the longest delay in neuronal signalling.

What accounts for the longest delay in neuronal signalling?

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