In the 23rd century, the Human neuron potential was measured in millivolts and neural sodium-potassium pump levels. Normal Human neuron resting potential measured at -70 millivolts, and topped at 30 millivolts for active potential. The sodium-[[potassium] channel states were sodium external, potassium external and internal. When a Human changed from resting to action potential, the neurons opened sodium gates. Sodium transitioned to interior, and the neural charge switched from -70mV to +30mV.
On stardate 2715.6, Earth year 2265, Devidians harmed the Human Starfleet crew at Drozana Station by feeding on their neural energy, throwing the sodium, potassium and millivolt levels out of order. Doctor Leonard H. McCoy enlisted the help of a visiting time traveler to treat neuronally depleted officers in an engineering bay. With the assistance, the doctor pioneered a neural rejuvenation procedure. First, the pair took readings from a drained lieutenant and a drained ensign. The lieutenant's readings indicated elevated exterior potassium, levels and neurons limited to a 15mV active potential. The sodium and potassium ions had been depleted, rendering some neurons incapable of electrical response. McCoy determined the likely cause to be as sudden change in neural voltage. This change in sodium, potassium and potential levels was predicted to lead to fatigue, blurred vision, dulled senses, and a loss of autonomic functions.
The drained ensign had suffered different damage. His resting potential read as -60mV to McCoy's tricorder. A scan of his neural sodium-potassium pump levels revealed elevated interior neuron sodium ion levels, and damaged sodium-potassium gate1s due to forcible ion movement. The tricorder's predicted results - hallucination, loss of motor function, and nervous system damage - appeared to match the ensign's symptoms.
McCoy's neural rejuvenation procedure consisted of a form of neurosurgery. The doctor calibrated a cortical stimulator to heal the Devidian victims' neuronal depletion. With the neurosurgery, the neuron charge at rest returned to positively-charged sodium ions exterior, and positively-charged potassium ions interior and exterior. For active potential, the neuron opened its sodium gates. Sodium transitioned to interior. Neural charge switches from -70mV to +30mV. After restoring the Human baseline for neural activity, McCoy prepared a hypospray and proceeded to the station's command center, where he healed station commander Captain Kendra Reaver while the time traveler removed the remaining Devidian presence. (STO - "Spectres" mission: "Everything Old is New")