Tetrodotoxin TTX is a very selective voltage-gated sodium channel blocker that is lethal in minimal doses. It has also served as an essential tool in neuroscience research. It, therefore, disrupts action potentials—but not the resting membrane potential—and can be used to silence neuronal activity. Its mechanism of action was demonstrated by Toshio Narahashi and John W.
Moore at Duke University, working on the giant lobster axon in Cardozo, David. Series B, Physical and Biological Sciences 84, no. To learn more about our GDPR policies click here. If you want more info regarding data storage, please contact gdpr jove. Your access has now expired. Provide feedback to your librarian. If you have any questions, please do not hesitate to reach out to our customer success team.
Login processing Chapter Nervous System. Chapter 1: Scientific Inquiry. Chapter 2: Chemistry of Life. Chapter 3: Macromolecules. Chapter 4: Cell Structure and Function.
Chapter 5: Membranes and Cellular Transport. Chapter 6: Cell Signaling. Chapter 7: Metabolism. Chapter 8: Cellular Respiration. Chapter 9: Photosynthesis. Chapter Cell Cycle and Division. Chapter Meiosis. Chapter Classical and Modern Genetics. Voltage-gated ion channels regulate the relative concentrations of different ions inside and outside the cell. The difference in total charge between the inside and outside of the cell is called the membrane potential. For quiescent cells, the relatively-static membrane potential is known as the resting membrane potential.
The resting membrane potential is at equilibrium since it relies on the constant expenditure of energy for its maintenance.
It is dominated by the ionic species in the system that has the greatest conductance across the membrane. For most cells, this is potassium. As potassium is also the ion with the most-negative equilibrium potential, usually the resting potential can be no more negative than the potassium equilibrium potential.
This voltage is called the resting membrane potential and is caused by differences in the concentrations of ions inside and outside the cell. If the membrane were equally permeable to all ions, each type of ion would flow across the membrane and the system would reach equilibrium.
The negative resting membrane potential is created and maintained by increasing the concentration of cations outside the cell in the extracellular fluid relative to inside the cell in the cytoplasm. The negative charge within the cell is created by the cell membrane being more permeable to potassium ion movement than sodium ion movement.
In neurons, potassium ions are maintained at high concentrations within the cell while sodium ions are maintained at high concentrations outside of the cell. The cell possesses potassium and sodium leakage channels that allow the two cations to diffuse down their concentration gradient.
However, the neurons have far more potassium leakage channels than sodium leakage channels. Therefore, potassium diffuses out of the cell at a much faster rate than sodium leaks in.
Because more cations are leaving the cell than are entering, this causes the interior of the cell to be negatively charged relative to the outside of the cell. The actions of the sodium potassium pump help to maintain the resting potential, once established. As more cations are expelled from the cell than taken in, the inside of the cell remains negatively charged relative to the extracellular fluid.
At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside that neuron. The resting potential tells about what happens when a neuron is at rest. An action potential occurs when a neuron sends information down an axon, away from the cell body. Neuroscientists use other words, such as a "spike" or an "impulse" for the action potential.
The action potential is an explosion of electrical activity that is created by a depolarizing current. This means that some event a stimulus causes the resting potential to move toward 0 mV. When the depolarization reaches about mV a neuron will fire an action potential.
This is the threshold. If the neuron does not reach this critical threshold level, then no action potential will fire. Also, when the threshold level is reached, an action potential of a fixed sized will always fire There are no big or small action potentials in one nerve cell - all action potentials are the same size.
Action potentials are caused when different ions cross the neuron membrane.
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