All cells, including neurons, are inherently electrical, because the fluid inside and outside a cell contains many ions and charged molecules. The different concentrations of ions inside and outside a cell results in a concentration gradient across the plasma membrane. Sodium ions (Na+) and chloride ions (Cl-) are more concentrated outside a cell than inside. Potassium ions (K+) and negatively charged proteins are more concentrated inside a cell than outside. A voltmeter can be used to measure the voltage, or electrical potential, across a plasma membrane. A recording electrode is placed in the cell’s cytoplasm, while a reference electrode is placed in the extracellular fluid. If there is an equal distribution of positive and negative charges on both sides of the membrane, no membrane potential exists, and the voltmeter reads zero millivolts (0 mV). The plasma membrane contains ion channels. A type of potassium channel, sometimes called a leak channel, is always open, allowing K+ to cross the membrane. Because the inside of the cell has a greater concentration of K+ than the outside, K+ tends to flow down its concentration gradient to the outside of the cell, leaving the inside with a net negative charge. This charge forms an electrochemical gradient across the membrane. At a voltage called the equilibrium potential, the negative charge is great enough that it opposes the outward net flow of the positively charged K+ ions. Most cells have a membrane potential of around -70 millivolts when they are at rest. This is called the resting potential. The leakage of K+ is largely responsible for this potential. Na+ and Cl- also leak across the membrane, but to a lesser extent. All animal cells have potassium leak channels, but neurons and other electrically excitable cells also have voltage-gated channels that allow them to produce a neural signal by making rapid changes in the membrane potential. The voltage-gated sodium and potassium channels are closed at the cell’s resting potential but open in response to specific changes in voltage, which may occur when the cell is stimulated by another cell. Researchers can artificially change the membrane potential to study the behavior of voltage-gated channels. Recall that at -70 millivolts, the channels are closed. As the membrane potential becomes less negative, a point is reached where the channels will open. The most negative voltage at which point these channels will open is -50. The concentration gradients of Na+ and K+ across the membrane provide a cell with a form of potential energy. These gradients are maintained by a pump in the membrane called the sodium-potassium pump. With each cycle, the pump takes up three Na+ ions from inside the cell. ATP phosphorylates the pump, giving it the energy to change shape and expel the Na+ ions to the outside. The pump then picks up two K+ ions from outside the cell, releases its phosphate group, and returns to its original conformation, releasing the K+ into the cell. If this pump did not operate, the ion concentration gradients across the membrane would soon disappear. These concentration gradients are essential for neurons to generate electrical signals, called action potentials.
Table of contents
- 1. Introduction to Biology2h 40m
- 2. Chemistry3h 40m
- 3. Water1h 26m
- 4. Biomolecules2h 23m
- 5. Cell Components2h 26m
- 6. The Membrane2h 31m
- 7. Energy and Metabolism2h 0m
- 8. Respiration2h 40m
- 9. Photosynthesis2h 49m
- 10. Cell Signaling59m
- 11. Cell Division2h 47m
- 12. Meiosis2h 0m
- 13. Mendelian Genetics4h 41m
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses16m
- Test Crosses14m
- Dihybrid Crosses20m
- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
- Pedigrees6m
- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
- X-Inactivation9m
- 14. DNA Synthesis2h 27m
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- 16. Regulation of Expression3h 31m
- Introduction to Regulation of Gene Expression13m
- Prokaryotic Gene Regulation via Operons27m
- The Lac Operon21m
- Glucose's Impact on Lac Operon25m
- The Trp Operon20m
- Review of the Lac Operon & Trp Operon11m
- Introduction to Eukaryotic Gene Regulation9m
- Eukaryotic Chromatin Modifications16m
- Eukaryotic Transcriptional Control22m
- Eukaryotic Post-Transcriptional Regulation28m
- Eukaryotic Post-Translational Regulation13m
- 17. Viruses37m
- 18. Biotechnology2h 58m
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- 20. Development1h 5m
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- 22. Evolution of Populations3h 52m
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- 24. History of Life on Earth2h 6m
- 25. Phylogeny2h 31m
- 26. Prokaryotes4h 59m
- 27. Protists1h 12m
- 28. Plants1h 22m
- 29. Fungi36m
- 30. Overview of Animals34m
- 31. Invertebrates1h 2m
- 32. Vertebrates50m
- 33. Plant Anatomy1h 3m
- 34. Vascular Plant Transport2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System10m
- 40. Circulatory System1h 57m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System4m
- 44. Animal Reproduction2m
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- 47. Muscle Systems23m
- 48. Ecology3h 11m
- Introduction to Ecology20m
- Biogeography14m
- Earth's Climate Patterns50m
- Introduction to Terrestrial Biomes10m
- Terrestrial Biomes: Near Equator13m
- Terrestrial Biomes: Temperate Regions10m
- Terrestrial Biomes: Northern Regions15m
- Introduction to Aquatic Biomes27m
- Freshwater Aquatic Biomes14m
- Marine Aquatic Biomes13m
- 49. Animal Behavior28m
- 50. Population Ecology3h 41m
- Introduction to Population Ecology28m
- Population Sampling Methods23m
- Life History12m
- Population Demography17m
- Factors Limiting Population Growth14m
- Introduction to Population Growth Models22m
- Linear Population Growth6m
- Exponential Population Growth29m
- Logistic Population Growth32m
- r/K Selection10m
- The Human Population22m
- 51. Community Ecology2h 46m
- Introduction to Community Ecology2m
- Introduction to Community Interactions9m
- Community Interactions: Competition (-/-)38m
- Community Interactions: Exploitation (+/-)23m
- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
44. Animal Reproduction
Animal Reproduction
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