what is the term used to describe transmission of an action potential along a myelinated axon

35.2B: Nerve Impulse Manual within a Neuron: Action Potential

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Signals are transmitted from neuron to neuron via an action potential, when the axon membrane rapidly depolarizes and repolarizes.

Learning Objectives

• Explain the formation of the action potential in neurons

Key Points

• Action potentials are formed when a stimulus causes the cell membrane to depolarize past the threshold of excitation, causing all sodium ion channels to open.
• When the potassium ion channels are opened and sodium ion channels are closed, the jail cell membrane becomes hyperpolarized every bit potassium ions leave the jail cell; the jail cell cannot burn during this refractory period.
• The action potential travels down the axon as the membrane of the axon depolarizes and repolarizes.
• Myelin insulates the axon to prevent leakage of the current as it travels down the axon.
• Nodes of Ranvier are gaps in the myelin forth the axons; they contain sodium and potassium ion channels, assuasive the action potential to travel apace downwardly the axon by jumping from i node to the next.

Key Terms

• action potential: a short term alter in the electrical potential that travels along a prison cell
• depolarization: a decrease in the difference in voltage between the within and exterior of the neuron
• hyperpolarize: to increase the polarity of something, especially the polarity across a biological membrane
• node of Ranvier: a small constriction in the myelin sheath of axons
• saltatory conduction: the process of regenerating the activeness potential at each node of Ranvier

Action Potential

A neuron can receive input from other neurons via a chemical chosen a neurotransmitter. If this input is strong enough, the neuron will pass the betoken to downstream neurons. Manual of a signal inside a neuron (in one management only, from dendrite to axon terminal) is carried out by the opening and endmost of voltage-gated ion channels, which cause a brief reversal of the resting membrane potential to create an action potential. As an action potential travels down the axon, the polarity changes across the membrane. One time the signal reaches the axon concluding, it stimulates other neurons.

Figure \(\PageIndex{i}\): Formation of an activity potential: The germination of an action potential can be divided into five steps. (1) A stimulus from a sensory jail cell or another neuron causes the target cell to depolarize toward the threshold potential. (2) If the threshold of excitation is reached, all Na+ channels open and the membrane depolarizes. (iii) At the peak action potential, Yard+ channels open and K+ begins to go out the cell. At the same time, Na+ channels close. (4) The membrane becomes hyperpolarized as K+ ions continue to leave the cell. The hyperpolarized membrane is in a refractory period and cannot fire. (five) The K+ channels shut and the Na+/K+ transporter restores the resting potential.

Depolarization and the Activity Potential

When neurotransmitter molecules bind to receptors located on a neuron's dendrites, voltage-gated ion channels open up. At excitatory synapses, positive ions alluvion the interior of the neuron and depolarize the membrane, decreasing the deviation in voltage between the inside and outside of the neuron. A stimulus from a sensory prison cell or another neuron depolarizes the target neuron to its threshold potential (-55 mV), and Na⁺ channels in the axon hillock open up, starting an action potential. Once the sodium channels open, the neuron completely depolarizes to a membrane potential of about +40 mV. The action potential travels down the neuron as Na+ channels open.

Hyperpolarization and Return to Resting Potential

Action potentials are considered an "all-or zippo" issue. In one case the threshold potential is reached, the neuron completely depolarizes. Every bit soon as depolarization is complete, the cell "resets" its membrane voltage back to the resting potential. The Na⁺ channels shut, beginning the neuron'southward refractory period. At the same time, voltage-gated K⁺ channels open up, allowing Chiliad⁺ to get out the cell. As K⁺ ions leave the prison cell, the membrane potential once once again becomes negative. The diffusion of G⁺ out of the cell hyperpolarizes the jail cell, making the membrane potential more negative than the prison cell's normal resting potential. At this signal, the sodium channels return to their resting country, ready to open over again if the membrane potential again exceeds the threshold potential. Eventually, the extra Chiliad⁺ ions diffuse out of the cell through the potassium leakage channels, bringing the cell from its hyperpolarized state back to its resting membrane potential.

Myelin and Propagation of the Action Potential

For an action potential to communicate information to another neuron, information technology must travel along the axon and reach the axon terminals where information technology can initiate neurotransmitter release. The speed of conduction of an activeness potential along an axon is influenced past both the diameter of the axon and the axon's resistance to electric current leak. Myelin acts as an insulator that prevents current from leaving the axon, increasing the speed of activity potential conduction. Diseases similar multiple sclerosis cause degeneration of the myelin, which slows activeness potential conduction because axon areas are no longer insulated so the current leaks.

Figure \(\PageIndex{1}\): Action potential travel along a neuronal axon: The action potential is conducted downward the axon equally the axon membrane depolarizes, and then repolarizes.

A node of Ranvier is a natural gap in the myelin sheath along the axon. These unmyelinated spaces are nigh one micrometer long and contain voltage gated Na⁺ and K⁺ channels. The flow of ions through these channels, particularly the Na⁺ channels, regenerates the action potential over and over again along the axon. Action potential "jumps" from one node to the next in saltatory conduction. If nodes of Ranvier were not present along an axon, the action potential would propagate very slowly; Na⁺ and K⁺ channels would have to continuously regenerate action potentials at every signal along the axon. Nodes of Ranvier also salve energy for the neuron since the channels only need to exist present at the nodes and not along the entire axon.

Effigy \(\PageIndex{1}\): Nodes of Ranvier: Nodes of Ranvier are gaps in myelin coverage forth axons. Nodes contain voltage-gated Grand+ and Na+ channels. Action potentials travel down the axon past jumping from ane node to the next.

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