Final answer:
Ions flowing through connexons do not occur during a chemical synapse, which is instead characterized by a chain of events involving action potentials, calcium ion influx, and neurotransmitter release through exocytosis. The correct option is D. Ions flow through connexons
Step-by-step explanation:
The event that does not occur during a chemical synapse is ions flowing through connexons. Connexons are involved in electrical synapses, not chemical ones. In a chemical synapse, an action potential invades the presynaptic terminal, leading to a series of steps that result in the release of neurotransmitters. These steps include voltage-gated Na+ channels opening, followed by the opening of voltage-gated Ca²+ channels.
Calcium ions trigger the fusion of synaptic vesicles with the presynaptic membrane, culminating in neurotransmitter release via exocytosis into the synaptic cleft. After release, neurotransmitters can be removed by glial cell uptake or enzymatic degradation, which prevents ongoing stimulation of the postsynaptic neuron. The correct option is D. Ions flow through connexons