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A neuron is an element of the nervous system that is responsible for receiving and transmitting information throughout the brain via electrochemical signals. Information travels through the brain in the form of an action potential or nerve impulse. This reverses the electrical charge of a resting neuron and its cell membrane potential. When a neuron is not generating an action potential, it is called a resting neuron. At rest, a neuron has an interior cell membrane that is negatively charged relative to the outside of the cell membrane.
A cell membrane is an external boundary around a neuron. It consists of a double layer of lipids or fats, and it is where proteins, such as ion channels, are found. The lipid bi-layer operates as a barrier and maintains a division of electrical charges across the cell membrane via ion pumps and ion channels. Ion pumps establish ion concentration gradients in the membrane and move ions into and out of the neuron against their concentration gradients. Ions channels work in opposition to ion pumps and allow certain ions to move across the cell membrane toward their concentration gradients.
The potential difference across the cell membrane of a resting neuron is called the resting membrane potential. It is the electrical energy across the membrane of an unstimulated, electrically excitable cell. Resting neuron potentials range from minus-60 millivolts (mV) to minus-90 millivolts but usually are minus-65 millivolts. Potential differences across the cell membrane occur because of disparities in the concentration of ions inside and outside of the cell and because cell membranes are permeable or porous to those particular ions.
A cell membrane has an intracellular fluid that has a high concentration of potassium ions, balanced by negatively charged ions or anions. The cell membrane is impermeable to these particular anions, which means that those ions are unable move across the cell membrane. The fluid outside the cell membrane constitutes a dilute solution of sodium chloride.
A resting neuron has an influx of sodium ions into the neuron, across the cell membrane via sodium ion channels. This is then balanced by an efflux of potassium ions via potassium ion channels. At rest, or when a neuronal membrane is polarized, the membrane potential remains near to the potassium equilibrium potential. This means that the neuronal membrane consists mostly of potassium ions. A neuronal membrane is depolarized when it receives an excitatory signal or an action potential, resulting in an influx of sodium ions and a neuron that is no longer resting or inactive.