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Medical Physiology - Resting Membrane Potential of Neurons
The resting membrane potential is determined by diffusion potentials, membrane permeability, and the electrogenic characteristics of the Na⁺-K⁺ pump. • Potassium diffusion potential. A potassium ion ratio of 35:1 from intracellular to extracellular environments generates a Nernst potential of 94 millivolts, as per the Nernst equation. Sodium diffusion potential. The sodium ion ratio from intracellular to extracellular space is 0.1, resulting in a computed Nernst potential of +61 millivolts.
• Permeability of membranes. The nerve fiber membrane's permeability to potassium is approximately 100 times greater than that to sodium, so potassium diffusion significantly influences the membrane potential. The application of this elevated permeability value in the Goldman equation results in an internal membrane potential of 86 millivolts, which approximates the potassium diffusion potential of 94 millivolts.
• Electrogenic characteristics of the Na⁺-K⁺ pump. The Na ion K ion pump extrudes three sodium ions from the cell for every two potassium ions it imports, resulting in a persistent reduction of positive charges within the membrane. The Na⁺-K⁺ pump is electrogenic as it generates a net deficit of positive ions within the cell, resulting in an internal negative charge of around 4 millivolts across the cell membrane.
The resting membrane potential is determined by diffusion potentials, membrane permeability, and the electrogenic characteristics of the Na⁺-K⁺ pump. • Potassium diffusion potential. A potassium ion ratio of 35:1 from intracellular to extracellular environments generates a Nernst potential of 94 millivolts, as per the Nernst equation. Sodium diffusion potential. The sodium ion ratio from intracellular to extracellular space is 0.1, resulting in a computed Nernst potential of +61 millivolts.
• Permeability of membranes. The nerve fiber membrane's permeability to potassium is approximately 100 times greater than that to sodium, so potassium diffusion significantly influences the membrane potential. The application of this elevated permeability value in the Goldman equation results in an internal membrane potential of 86 millivolts, which approximates the potassium diffusion potential of 94 millivolts.
• Electrogenic characteristics of the Na⁺-K⁺ pump. The Na ion K ion pump extrudes three sodium ions from the cell for every two potassium ions it imports, resulting in a persistent reduction of positive charges within the membrane. The Na⁺-K⁺ pump is electrogenic as it generates a net deficit of positive ions within the cell, resulting in an internal negative charge of around 4 millivolts across the cell membrane.
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