![]() ![]() Think of it like sending an email or a text message. There is no in-between, and there is no turning off an action potential once it starts. In simple terms, this means that an incoming signal from another neuron is either sufficient or insufficient to reach the threshold of excitation. The action potential is an all-or-none phenomenon. You can view the transcript for “Lights, Camera, Action Potentials!” here (opens in new window). The process of neural communication is explained in the following video. At first, it hyperpolarizes, becoming slightly more negative than the resting potential, and then it levels off, returning to the resting potential. As positively charged potassium ions leave, the cell quickly begins repolarization. At the peak of the spike, the sodium gates close and the potassium gates open. Many additional pores open, causing a massive influx of Na + ions and a huge positive spike in the membrane potential, the peak action potential. The process of when the cell’s charge becomes positive, or less negative, is called depolarization. If the charge reaches a certain level, called the threshold of excitation, the neuron becomes active and the action potential begins. With this influx of positive ions, the internal charge of the cell becomes more positive. When a neuron receives signals at the dendrites-due to neurotransmitters from an adjacent neuron binding to its receptors-small pores, or gates, open on the neuronal membrane, allowing Na + ions, propelled by both charge and concentration differences, to move into the cell. Other molecules, such as chloride ions (yellow circles) and negatively charged proteins (brown squares), help contribute to a positive net charge in the extracellular fluid and a negative net charge in the intracellular fluid.įrom this resting potential state, the neuron receives a signal, and its state changes abruptly (Figure 2). At resting potential, Na + (blue pentagons) is more highly concentrated outside the cell in the extracellular fluid (shown in blue), whereas K + (purple squares) is more highly concentrated near the membrane in the cytoplasm or intracellular fluid. This provides an additional force on sodium, causing it to move into the cell.įigure 1. In addition, the inside of the cell is slightly negatively charged compared to the outside. Potassium (K +), on the other hand, is more concentrated inside the cell, and will tend to move out of the cell (Figure 1). In the resting state, sodium (Na +) is at higher concentrations outside the cell, so it will tend to move into the cell. Ions in high-concentration areas are ready to move to low-concentration areas, and positive ions are ready to move to areas with a negative charge. Like a rubber band stretched out and waiting to spring into action, ions line up on either side of the cell membrane, ready to rush across the membrane when the neuron goes active and the membrane opens its gates (i.e., a sodium-potassium pump that allows movement of ions across the membrane). The semipermeable nature of the neuronal membrane somewhat restricts the movement of these charged molecules, and, as a result, some of the charged particles tend to become more concentrated either inside or outside the cell.īetween signals, the neuron membrane’s potential is held in a state of readiness, called the resting potential. The electrical charge of the fluids is caused by charged molecules (ions) dissolved in the fluid. This difference in charge across the membrane, called the membrane potential, provides energy for the signal. The neuronal membrane keeps these two fluids separate-a critical role because the electrical signal that passes through the neuron depends on the intra- and extracellular fluids being electrically different. The neuron exists in a fluid environment-it is surrounded by extracellular fluid and contains intracellular fluid (i.e., cytoplasm). Now that we have learned about the basic structures of the neuron and the role that these structures play in neuronal communication, let’s take a closer look at the signal itself-how it moves through the neuron and then jumps to the next neuron, where the process is repeated. Explain how drugs act as agonists or antagonists for a given neurotransmitter system.Describe how neurons communicate with each other.
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