An unusual property of the neuron is its capability for cell-to-cell communication via synapses, known to be the neuron-level "protophenomenon" underlying the brain-level "real phenomenon" of cognition. The temporal synchronization of such synaptic activity is the leading candidate for explaining "cognitive binding" and therefore the unity of mind. An equally-unusual property of the neuron is the action potential, the means by which the neuron sends a signal down the axon. Although infrequently noted by researchers in relation to consciousness, signal propagation within the neuron entails the momentary permeability of the neuronal membrane, allowing a massive influx of charged ions into the cellular interior. Such openness to the extracellular world is arguably the protophenomenon of neuronal "sentience," literally, feeling the charge-state of the electrochemical environment. Sensitivity to the external pH is a common feature of all living cells, but is greatly amplified during the neuron's action potential. Synchronization of the action potentials of the same neurons that are involved in cognitive binding is the likely mechanism by which the sentience of individual neurons is coordinated into the brain-level phenomenon of subjective awareness. I conclude that a proper understanding of the permeability of the neuronal membrane during the action potential is as important for consciousness studies as is a proper understanding of synaptic transmission for the explication of the cognition made possible by neurons.