The Na+/K+-ATPase enzyme is perhaps the most crucial membrane pump found in neurons for each ATP molecule hydrolyzed, this enzyme extrudes three Na+ ions and intakes two K+ ions. To preserve the chemical and electrical gradients necessary for the initiation of an action potential, various membrane proteins must work to transport ions across the cell surface. The opening and closing of Na+ and K+ channels during an action potential make electrical signals an active process, yet membrane pumps and channels must also be active to maintain the resting membrane potential. By convention, the potential outside the neuron is arbitrarily defined as zero, and the relative number of intracellular negative charges creates a potential difference across the plasma membrane this is why resting potentials are expressed as negative values. In contrast, when cells are at rest, or when there is a lack of electrical signaling, they maintain a resting membrane potential of approximately -60 to -70 mV. The pattern or frequency of action potentials define a neuron's ability to transmit information throughout the nervous system. The rising phase of the action potential is caused by an influx of Na+, while the falling phase of the action potential is caused by a later increase permeability to K+.
This depolarizes the membrane and brings the potential closer to the equilibrium potential of Na+ (~ +50mV).Īn increase in ionic conductance in the membrane of the axon results in an increase in the action potential. However, during an action potential, the permeability to Na+ is dramatically increased by the opening of Na+ channels. At rest, the membrane is most permeable to K+ thus, the resting potential is closest to the equilibrium potential of K+ (~ -110mV). This creates a driving force for K+ to go out of the cell and Na+ to come into the cell. is higher inside the neuron while is higher outside the neuron. Membrane potential is determined by the equilibrium potential and relative permeabilities of the ions in the system. In the neuron, the major ions in play are potassium (K+) and sodium (Na+). This difference arises from the separation of electric charges across the resistive membrane barrier. Action potentials enable nerve cells to carry signals over long distances.Īction Potentials are Initiated by a Change in Membrane PotentialĪ neuron at rest maintains an electrical potential difference across its membrane. Action potentials are self-regenerating and occur spontaneously when the membrane is depolarized to a critical voltage called the threshold. It is a brief, explosive change in membrane potential which goes from a negative to a positive potential.
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