A brief electrical charge that travels down the axon of a neuron is called the
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A neuron (a nerve cell) is the basic building block of the nervous system. When neurons transmit signals through the body, part of the transmission process involves an electrical impulse called an action potential. Show
This process, which occurs during the firing of the neurons, allows a nerve cell to transmit an electrical signal down the axon (a portion of the neuron that carries nerve impulses away from the cell body) toward other cells. This sends a message to the muscles to provoke a response. For example, say you want to pick up a glass so you can take a drink of water. The action potential plays a key role in carrying that message from the brain to the hand. Prior to the Action PotentialWhen a neuron is not sending signals, the inside of the neuron has a negative charge relative to the positive charge outside the cell. Electrically charged atoms known as ions maintain the positive and negative charge balance. Calcium contains two positive charges, sodium and potassium contain one positive charge, and chloride contains a negative charge. When at rest, the cell membrane of the neuron allows certain ions to pass through while preventing or restricting other ions from moving. In this state, sodium and potassium ions cannot easily pass through the membrane. Chloride ions, however, are able to freely cross the membrane. The negative ions inside the cell are unable to cross the barrier. The resting potential of the neuron refers to the difference between the voltage inside and outside the neuron. The resting potential of the average neuron is around -70 millivolts, indicating that the inside of the cell is 70 millivolts less than the outside of the cell. At this point, the brain has not yet sent the message to the hand to pick up the glass, but the neuron is ready to receive the signal. How Neurons Transmit Information During the Action PotentialYou’ve decided that you are thirsty and would like a drink of water. Your brain starts the chain of events to send a message to the muscles in your hand that you need to pick up the glass. When a nerve impulse (which is how neurons communicate with one another) is sent out from a cell body, the sodium channels in the cell membrane open and the positive sodium cells surge into the cell. Once the cell reaches a certain threshold, an action potential will fire, sending the electrical signal down the axon. The sodium channels play a role in generating the action potential in excitable cells and activating a transmission along the axon. Action potentials either happen or they don't; there is no such thing as a "partial" firing of a neuron. This principle is known as the all-or-none law. This means that neurons always fire at their full strength. This ensures that the full intensity of the signal is carried down the nerve fiber and transferred to the next cell and that the signal does not weaken or become lost the further it travels from the source. The message from the brain is now traveling down the nerves to the muscles in the hand. After the Action PotentialAfter the neuron has fired, there is a refractory period in which another action potential is not possible. The refractory period generally lasts one millisecond. During this time, the potassium channels reopen and the sodium channels close, gradually returning the neuron to its resting potential. Once the neuron has "recharged," it is possible for another action potential to occur and transmit the signal down the length of the axon. Through this continual process of firing then recharging, the neurons are able to carry the message from the brain to tell the muscles what to do—hold the glass, take a sip, or put it down. \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)
When Lightning StrikesThis amazing cloud-to-surface lightning occurred when a difference in electrical charge built up in a cloud relative to the ground. When the buildup of charge was great enough, a sudden discharge of electricity occurred. A nerve impulse is similar to a lightning strike. Both a nerve impulse and a lightning strike occur because of differences in electrical charge, and both result in an electric current. Generating Nerve ImpulsesA nerve impulse, like a lightning strike, is an electrical phenomenon. A nerve impulse occurs because of a difference in electrical charge across the plasma membrane of a neuron. How does this difference in electrical charge come about? The answer involves ions, which are electrically charged atoms or molecules. Resting PotentialWhen a neuron is not actively transmitting a nerve impulse, it is in a resting state, ready to transmit a nerve impulse. During the resting state, the sodium-potassium pump maintains a difference in charge across the cell membrane of the neuron. The sodium-potassium pump is a mechanism of active transport that moves sodium ions out of cells and potassium ions into cells. The sodium-potassium pump moves both ions from areas of lower to higher concentration, using energy in ATP and carrier proteins in the cell membrane. Figure \(\PageIndex{3}\)shows in greater detail how the sodium-potassium pump works. Sodium is the principal ion in the fluid outside of cells, and potassium is the principal ion in the fluid inside of cells. These differences in concentration create an electrical gradient across the cell membrane, called resting potential. Tightly controlling membrane resting potential is critical for the transmission of nerve impulses. Action PotentialAn action potential, also called a nerve impulse, is an electrical charge that travels along the membrane of a neuron. It can be generated when a neuron’s membrane potential is changed by chemical signals from a nearby cell. In an action potential, the cell membrane potential changes quickly from negative to positive as sodium ions flow into the cell through ion channels, while potassium ions flow out of the cell, as shown in Figure \(\PageIndex{3}\). The change in membrane potential results in the cell becoming depolarized. An action potential works on an all-or-nothing basis. That is, the membrane potential has to reach a certain level of depolarization, called the threshold, otherwise, an action potential will not start. This threshold potential varies but is generally about 15 millivolts (mV) more positive than the cell's resting membrane potential. If a membrane depolarization does not reach the threshold level, an action potential will not happen. You can see in Figure \(\PageIndex{4}\) that two depolarizations did not reach the threshold level of -55mV. The first channels to open are the sodium ion channels, which allow sodium ions to enter the cell. The resulting increase in positive charge inside the cell (up to about +40 mV) starts the action potential. This is called the depolarization of the membrane. Potassium ion channels then open, allowing potassium ions to flow out of the cell, which ends the action potential. The inside of the membrane becomes negative again. This is called repolarization of the membrane. Both of the ion channels then close, and the sodium-potassium pump restores the resting potential of -70 mV. The action potential will move down the axon toward the synapse like a wave would move along the surface of the water. Figure \(\PageIndex{4}\)shows the change in potential of the axon membrane during an action potential. The nerve goes through a brief refractory period before racing resting potential. During the refractory period, another action potential cannot be generated In myelinated neurons, ion flows occur only at the nodes of Ranvier. As a result, the action potential signal "jumps" along the axon membrane from node to node rather than spreading smoothly along the membrane, as they do in axons that do not have a myelin sheath. This is due to a clustering of Na+ and K+ ion channels at the Nodes of Ranvier. Unmyelinated axons do not have nodes of Ranvier, and ion channels in these axons are spread over the entire membrane surface. Transmitting Nerve ImpulsesThe place where an axon terminal meets another cell is called a synapse. This is where the transmission of a nerve impulse to another cell occurs. The cell that sends the nerve impulse is called the presynaptic cell, and the cell that receives the nerve impulse is called the postsynaptic cell. Some synapses are purely electrical and make direct electrical connections between neurons. However, most synapses are chemical synapses. The transmission of nerve impulses across chemical synapses is more complex. Chemical SynapsesAt a chemical synapse, both the presynaptic and postsynaptic areas of the cells are full of the molecular machinery that is involved in the transmission of nerve impulses. As shown in Figure \(\PageIndex{5}\), the presynaptic area contains many tiny spherical vessels called synaptic vesicles that are packed with chemicals called neurotransmitters. When an action potential reaches the axon terminal of the presynaptic cell, it opens channels that allow calcium to enter the terminal. Calcium causes synaptic vesicles to fuse with the membrane, releasing their contents into the narrow space between the presynaptic and postsynaptic membranes. This area is called the synaptic cleft. The neurotransmitter molecules travel across the synaptic cleft and bind to receptors, which are proteins that are embedded in the membrane of the postsynaptic cell. The effect of a neurotransmitter on a postsynaptic cell depends mainly on the type of receptors that it activates, making it possible for a particular neurotransmitter to have different effects on various target cells. A neurotransmitter might excite one set of target cells, inhibit others, and have complex modulatory effects on still others, depending on the type of receptors. However, some neurotransmitters have relatively consistent effects on other cells. Review
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This page titled 11.4: Nerve Impulses is shared under a CK-12 license and was authored, remixed, and/or curated by Suzanne Wakim & Mandeep Grewal via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request. What is the brief electrical charge that travels down an axon called quizlet?A neural impulse; a brief electrical charge that travels down an axon.
What is the impulse that travels down a neuron's axon quizlet?the neural impulse( action potential) is electrical signal traveling down the axon.
What is the brief electrical charge that travels down an axon called a action potential B resting potential C allThis action potential is a n electrical ripple of positive ions flooding in to the negatively charged space inside the cell membrane, a process that repeats itself down the axon to the axon terminal, triggering the release of neurotransmitters into the next synaptic clef.
What is the electrical charge of a neuron at rest quizlet?The resting membrane potential of a neuron is about -70 mV (mV=millivolt) - this means that the inside of the neuron is 70 mV less than the outside.
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