Final answer:
In the resting state of a neuron, sodium ions (Na+) are found outside, and potassium ions (K+) inside, contributing to a negative resting membrane potential, maintained by the energy-consuming sodium-potassium pump.
Step-by-step explanation:
In the resting state of a neuron, you would primarily find sodium ions (Na+) outside the neuron and potassium ions (K+) inside the neuron. This distribution contributes to the cell's resting potential, which is a difference in charge across the neuron's membrane, with the inside being approximately 70 millivolts (mV) more negative than the outside.
The resting membrane potential is maintained by the sodium-potassium pump, which actively transports three Na+ ions out of the cell for every two K+ ions it brings in, using up one molecule of ATP for each cycle. As a consequence, more positive ions are outside the cell than inside, contributing to the negative charge of the neuron. These different ion concentrations are made possible because of ion channels providing selective permeability as well as the presence of leakage channels that allow for some passive ion movement.
In its resting state, the cell uses a large amount of its energy (up to 50%) to maintain this ionic gradient; this is essential for the neuron's capacity to fire action potentials in response to stimuli.