A mutation disables calcium binding by synaptotagmin in a sensory neuron while all SNARE proteins remain intact. During repeated action potentials, which defect appears?

Core Concept

Synaptotagmin is the calcium sensor that converts arriving calcium into a fusogenic push, displacing blocking factors and driving the SNARE bundle through final zippering. Without calcium binding, vesicles still dock and prime, yet the trigger step stalls, so release probability collapses despite normal calcium entry through channels. Fusion machinery present but untriggered matches the data.