The role of quantum processes in brain activity has been discussed intensively in recent years. Some authors regard the indeterminacy of quantum events as key property to relate brain activity and consciousness on a scientific basis. Here we ask the question where quantum events could be effective in the complex cortical structure. We argue that only elementary microscopic processes like electron transfer in protein complexes are able to survive thermal fluctuations. A model for the quantal emission process at the synaptic cleft is presented and related to the mechanism of electron transfer between different molecular states, as described by Marcus theory.