What is the trigger zone? Where is the trigger zone found in efferent, afferent, and interneurons? Do the terms trigger zone and axon hillock have the same meaning? Explain.
What will be an ideal response?
The trigger zone is an area of the neuron that contains a high membrane concentration of voltage-gated Na+ channels and is near an area that lacks these. In order for action potentials to occur, graded potentials reaching the trigger zone must depolarize the membrane to the threshold voltage. In efferent and interneurons, the trigger zone is the axon hillock (also called the initial segment). In afferent neurons, the trigger zone is located where the dendrites join the axon (immediately adjacent to the receptor), rather than at the axon hillock. The axon hillock is an anatomical region, whereas the trigger zone is defined by its function rather than its location.
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