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All questions of Neuron Membrane Potentials for MCAT Exam
Which ion primarily contributes to the resting membrane potential of a neuron?- a)Sodium (Na+)
- b)Potassium (K+)
- c)Calcium (Ca2+)
- d)Chloride (Cl-)
Correct answer is option 'B'. Can you explain this answer?
Which ion primarily contributes to the resting membrane potential of a neuron?
a)
Sodium (Na+)
b)
Potassium (K+)
c)
Calcium (Ca2+)
d)
Chloride (Cl-)
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Joseph Garcia answered |
Understanding Resting Membrane Potential
The resting membrane potential of a neuron is primarily determined by the distribution and permeability of various ions across the neuronal membrane. The ion that plays the most significant role in establishing this potential is potassium (K+).
Role of Potassium (K+)
- High Intracellular Concentration: Neurons typically have a much higher concentration of K+ ions inside the cell compared to the outside.
- Selective Permeability: The neuronal membrane is more permeable to K+ than to other ions when at rest. This is due to the presence of potassium channels that allow K+ to flow out of the cell.
- Equilibrium Potential: As K+ ions exit the neuron, they carry a positive charge with them, leading to a more negative charge inside the cell. The point at which the movement of K+ ions out of the cell balances the electrical gradient is known as the equilibrium potential for potassium, contributing to the overall resting membrane potential.
Comparison with Other Ions
- Sodium (Na+): While Na+ is crucial for generating action potentials, its resting permeability is lower than that of K+. Consequently, it contributes less to the resting membrane potential.
- Calcium (Ca2+) and Chloride (Cl-): Calcium plays a significant role in neurotransmitter release but is not a major contributor to the resting potential. Chloride ions also influence membrane potential but are less critical than K+.
Conclusion
In summary, the resting membrane potential is primarily influenced by the high permeability of the neuronal membrane to potassium ions, making K+ the principal ion responsible for maintaining this potential. Understanding this concept is vital for comprehending neuronal excitability and signaling.
The resting membrane potential of a neuron is primarily determined by the distribution and permeability of various ions across the neuronal membrane. The ion that plays the most significant role in establishing this potential is potassium (K+).
Role of Potassium (K+)
- High Intracellular Concentration: Neurons typically have a much higher concentration of K+ ions inside the cell compared to the outside.
- Selective Permeability: The neuronal membrane is more permeable to K+ than to other ions when at rest. This is due to the presence of potassium channels that allow K+ to flow out of the cell.
- Equilibrium Potential: As K+ ions exit the neuron, they carry a positive charge with them, leading to a more negative charge inside the cell. The point at which the movement of K+ ions out of the cell balances the electrical gradient is known as the equilibrium potential for potassium, contributing to the overall resting membrane potential.
Comparison with Other Ions
- Sodium (Na+): While Na+ is crucial for generating action potentials, its resting permeability is lower than that of K+. Consequently, it contributes less to the resting membrane potential.
- Calcium (Ca2+) and Chloride (Cl-): Calcium plays a significant role in neurotransmitter release but is not a major contributor to the resting potential. Chloride ions also influence membrane potential but are less critical than K+.
Conclusion
In summary, the resting membrane potential is primarily influenced by the high permeability of the neuronal membrane to potassium ions, making K+ the principal ion responsible for maintaining this potential. Understanding this concept is vital for comprehending neuronal excitability and signaling.
Which statement describes the membrane potential at the peak of an action potential?- a)The membrane potential is the same as the Na+ equilibrium potential.
- b)The membrane potential is slightly less positive than the Na+ equilibrium potential.
- c)The membrane potential is slightly more positive than the Na+ equilibrium potential.
- d)The membrane potential is much more positive than the Na+ equilibrium potential.
Correct answer is option 'B'. Can you explain this answer?
Which statement describes the membrane potential at the peak of an action potential?
a)
The membrane potential is the same as the Na+ equilibrium potential.
b)
The membrane potential is slightly less positive than the Na+ equilibrium potential.
c)
The membrane potential is slightly more positive than the Na+ equilibrium potential.
d)
The membrane potential is much more positive than the Na+ equilibrium potential.
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Orion Classes answered |
During the peak of an action potential, the membrane potential is not exactly equal to the Na+ equilibrium potential but rather slightly less positive. This is because the voltage-gated Na+ channels begin to close, leading to a decrease in the influx of Na+ ions and a subsequent repolarization of the membrane. The membrane potential returns to a negative value during the repolarization phase. Thank you for pointing out the error.
Researchers use genetic engineering techniques to culture neuronal cells with sodium-potassium pumps that, for each molecule of ATP, transport 2 sodium cations for every 3 potassium cations; assuming that all other aspects are held equal, which of the following would be most affected by this change, as compared to what happens in a normal neuronal cell?- a)The diffusion force on potassium cations would be larger and in the opposite direction
- b)The diffusion force on potassium cations would be smaller and in the same direction
- c)The diffusion force on potassium cations would be larger and in the same direction
- d)The diffusion force on potassium cations would be smaller and in the opposite direction
Correct answer is option 'C'. Can you explain this answer?
Researchers use genetic engineering techniques to culture neuronal cells with sodium-potassium pumps that, for each molecule of ATP, transport 2 sodium cations for every 3 potassium cations; assuming that all other aspects are held equal, which of the following would be most affected by this change, as compared to what happens in a normal neuronal cell?
a)
The diffusion force on potassium cations would be larger and in the opposite direction
b)
The diffusion force on potassium cations would be smaller and in the same direction
c)
The diffusion force on potassium cations would be larger and in the same direction
d)
The diffusion force on potassium cations would be smaller and in the opposite direction
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Orion Classes answered |
When the sodium-potassium pump transports 2 sodium cations out of the cell for every 3 potassium cations it brings into the cell, there will be an increased intracellular concentration of potassium ions. This higher intracellular concentration creates a larger concentration gradient, resulting in a larger diffusion force for potassium ions moving out of the cell. The diffusion force acts in the same direction as the concentration gradient, which is from the intracellular space to the extracellular space. Therefore, the diffusion force on potassium cations would be larger and in the same direction.
How are potassium ions typically moved out of a neuron when the membrane is at rest?- a)Electrical gradients move potassium ions out of the cell.
- b)The sodium-potassium pump moves potassium ions out of the cell.
- c)Potassium ions are stable and do not move when a membrane is at rest.
- d)Concentration gradients move potassium ions out of the cell.
Correct answer is option 'D'. Can you explain this answer?
How are potassium ions typically moved out of a neuron when the membrane is at rest?
a)
Electrical gradients move potassium ions out of the cell.
b)
The sodium-potassium pump moves potassium ions out of the cell.
c)
Potassium ions are stable and do not move when a membrane is at rest.
d)
Concentration gradients move potassium ions out of the cell.
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Orion Classes answered |
At rest, the concentration of potassium ions (K+) is higher inside the neuron compared to the extracellular environment. This concentration gradient drives the passive movement of potassium ions out of the cell through specific potassium channels. This movement helps to maintain the resting membrane potential by balancing the tendency of potassium ions to diffuse out of the cell.
The sodium-potassium pump (option B) is responsible for actively transporting potassium ions back into the cell and sodium ions out of the cell, but it is not the primary mechanism for moving potassium ions out of the cell when the membrane is at rest. I apologize for the confusion in my previous response.
Which of the following factors does not affect the speed of action potential propagation?- a)Axon diameter
- b)Myelination
- c)Temperature
- d)Resting membrane potential
Correct answer is option 'D'. Can you explain this answer?
Which of the following factors does not affect the speed of action potential propagation?
a)
Axon diameter
b)
Myelination
c)
Temperature
d)
Resting membrane potential
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Orion Classes answered |
The speed of action potential propagation is influenced by factors such as axon diameter, myelination, and temperature. The resting membrane potential, although important for neuronal function, does not directly impact the speed of action potential propagation.
Saltatory conduction refers to which of the following?- a)The conduction of an action potential along a demyelinated axon.
- b)The conduction of a graded potential along a myelinated axon.
- c)The conduction of a graded potential along a demyelinated axon.
- d)The conduction of an action potential along a myelinated axon.
Correct answer is option 'D'. Can you explain this answer?
Saltatory conduction refers to which of the following?
a)
The conduction of an action potential along a demyelinated axon.
b)
The conduction of a graded potential along a myelinated axon.
c)
The conduction of a graded potential along a demyelinated axon.
d)
The conduction of an action potential along a myelinated axon.
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Orion Classes answered |
Saltatory conduction refers to the rapid conduction of action potentials in myelinated axons. In a myelinated axon, the myelin sheath acts as an insulating layer, preventing the leakage of electrical charge across the membrane. The action potential "jumps" from one node of Ranvier to the next, where the myelin sheath is interrupted, rather than propagating continuously along the entire length of the axon. This saltatory conduction allows for faster and more efficient transmission of the action potential, as it skips the depolarization and repolarization steps in the myelinated regions.
Absolute and relative refractory periods are important aspects of which of the following?- a)Equilibrium potentials
- b)Action potentials
- c)Resting potentials
- d)Graded potentials
Correct answer is option 'B'. Can you explain this answer?
Absolute and relative refractory periods are important aspects of which of the following?
a)
Equilibrium potentials
b)
Action potentials
c)
Resting potentials
d)
Graded potentials
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Orion Classes answered |
Absolute and relative refractory periods are important aspects of action potentials.
During an action potential, there are specific periods of time where the neuron is unresponsive or less responsive to further depolarization and the generation of another action potential. These periods are known as refractory periods.
The absolute refractory period is the initial phase of the refractory period where the neuron is completely unresponsive to further stimulation. This period coincides with the depolarization and repolarization phases of the action potential.
The relative refractory period follows the absolute refractory period. During this phase, the neuron is still in a refractory state but can be stimulated with a stronger-than-normal stimulus to generate another action potential.
Therefore, the correct answer is option B: Action potentials.
In the resting state, which of the following mineral ions has an electrical force vector pointing out of the neuron?- a)Potassium cation
- b)Chloride anion
- c)alcium cation
- d)Sodium cation
Correct answer is option 'B'. Can you explain this answer?
In the resting state, which of the following mineral ions has an electrical force vector pointing out of the neuron?
a)
Potassium cation
b)
Chloride anion
c)
alcium cation
d)
Sodium cation
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Orion Classes answered |
In the resting state, the electrical force vector (positive charge) points out of the neuron for chloride ions (Cl-). Chloride ions have a negative charge, and as a result, they are attracted to the positively charged exterior of the neuron. This creates an electrical force that tends to drive chloride ions out of the neuron.
The concentration of chloride ions inside the neuron is relatively low compared to the extracellular concentration, and the membrane is permeable to chloride ions. Therefore, chloride ions tend to move out of the neuron, driven by the electrical force and concentration gradient.
On the other hand, potassium ions (K+), calcium ions (Ca2+), and sodium ions (Na+) have positive charges and are found in higher concentrations inside the neuron. The electrical force vectors for these ions point into the neuron, attracting them toward the negatively charged interior.
The resting potential for a particular neuron is measured to be -60 mV. Which of the following distributions of ions could not produce this measurement?- a)More cations than anions on both sides of the cell membrane
- b)More anions than cations on both sides of the cell membrane
- c)More anions than cations on the outside of the membrane, more cations than anions on the inside of the membrane
- d)More cations than anions on the outside of the membrane, more anions than cations on the inside of the membrane
Correct answer is option 'C'. Can you explain this answer?
The resting potential for a particular neuron is measured to be -60 mV. Which of the following distributions of ions could not produce this measurement?
a)
More cations than anions on both sides of the cell membrane
b)
More anions than cations on both sides of the cell membrane
c)
More anions than cations on the outside of the membrane, more cations than anions on the inside of the membrane
d)
More cations than anions on the outside of the membrane, more anions than cations on the inside of the membrane
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Orion Classes answered |
A resting potential of -60 mV is typically achieved by having more anions (negatively charged ions) inside the neuron compared to the outside and more cations (positively charged ions) outside the neuron compared to the inside. This creates an electrochemical gradient across the cell membrane.
Option C describes a distribution where there are more anions than cations on the outside of the membrane and more cations than anions on the inside of the membrane. This distribution would result in a net negative charge inside the neuron, contributing to a resting potential of -60 mV.
In the resting state, which of the following mineral ions is found in greatest concentration inside a neuron?- a)Sodium cation
- b)Calcium cation
- c)Chloride anion
- d)Potassium cation
Correct answer is option 'D'. Can you explain this answer?
In the resting state, which of the following mineral ions is found in greatest concentration inside a neuron?
a)
Sodium cation
b)
Calcium cation
c)
Chloride anion
d)
Potassium cation
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Orion Classes answered |
In the resting state, the concentration of potassium ions (K+) is highest inside a neuron compared to other mineral ions. This is due to the active transport of potassium ions by the sodium-potassium pump, which pumps potassium ions into the cell while simultaneously pumping sodium ions out of the cell. This creates a concentration gradient, with a higher concentration of potassium ions inside the neuron.
The resting membrane potential is primarily determined by the permeability of the cell membrane to potassium ions. The high concentration of potassium ions inside the neuron and the selective permeability of the membrane to potassium ions contribute to the negative resting membrane potential, typically around -70 mV.
Sodium ions (Na+), calcium ions (Ca2+), and chloride ions (Cl-) also play important roles in neuronal function, but their concentrations are relatively lower inside the neuron compared to potassium ions in the resting state.
What is the primary difference in graded potentials versus actions potentials?- a)Graded potentials occur in neurons of the peripheral nervous system, while actions potentials occur in neurons of the central nervous system
- b)Graded potentials occur in axons, while action potentials occur in the dendrites and soma
- c)Action potentials occur in axons, while graded potentials occur in the dendrites and soma
- d)Graded potentials do not involve transient production of charged molecules inside the neuron, while action potentials involve the flow of charged molecules across the neuron membrane
Correct answer is option 'C'. Can you explain this answer?
What is the primary difference in graded potentials versus actions potentials?
a)
Graded potentials occur in neurons of the peripheral nervous system, while actions potentials occur in neurons of the central nervous system
b)
Graded potentials occur in axons, while action potentials occur in the dendrites and soma
c)
Action potentials occur in axons, while graded potentials occur in the dendrites and soma
d)
Graded potentials do not involve transient production of charged molecules inside the neuron, while action potentials involve the flow of charged molecules across the neuron membrane
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Orion Classes answered |
The primary difference between graded potentials and action potentials is their location within the neuron. Graded potentials occur in the dendrites and soma (cell body) of the neuron, where they are generated in response to incoming signals from other neurons or sensory stimuli. Graded potentials can be either depolarizing (excitatory) or hyperpolarizing (inhibitory) and their magnitude varies depending on the strength of the stimulus.
On the other hand, action potentials occur in the axons of the neuron. They are all-or-nothing events that are initiated when a graded potential reaches a certain threshold. Action potentials are characterized by a rapid and brief depolarization followed by repolarization of the neuron membrane. They are responsible for the long-distance transmission of signals along the axon, allowing information to be communicated between different regions of the nervous system.
Nematodes are small worm-like animals with roughly 300 neurons. Imagine that a mutation is introduced into a population of nematodes that down-regulates the production of Schwann cells. Which of the following phenotypes would you predict to have a selective advantage in the population?- a)Nematodes with smaller diameter axons
- b)Nematodes with shorter axons
- c)Nematodes with longer axons
- d)Nematodes with larger soma
Correct answer is option 'B'. Can you explain this answer?
Nematodes are small worm-like animals with roughly 300 neurons. Imagine that a mutation is introduced into a population of nematodes that down-regulates the production of Schwann cells. Which of the following phenotypes would you predict to have a selective advantage in the population?
a)
Nematodes with smaller diameter axons
b)
Nematodes with shorter axons
c)
Nematodes with longer axons
d)
Nematodes with larger soma
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Orion Classes answered |
In the absence of Schwann cells and myelination, the efficiency of nerve impulse conduction would be reduced. Axons with shorter lengths would experience less attenuation of the electrical signal, allowing for better propagation of the nerve impulses along the axon. Shorter axons would result in a smaller distance for the nerve impulses to travel, leading to faster and more reliable transmission of signals within the nervous system.
Therefore, nematodes with shorter axons would have an adaptive advantage in terms of maintaining efficient neural communication in the absence of Schwann cells and myelination.
Action potentials are characterized by which of the following?- a)Depolarization or hyperpolarization
- b)Slightly negative polarization
- c)Rapid depolarization
- d)Repolarization
Correct answer is option 'C'. Can you explain this answer?
Action potentials are characterized by which of the following?
a)
Depolarization or hyperpolarization
b)
Slightly negative polarization
c)
Rapid depolarization
d)
Repolarization
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Orion Classes answered |
During an action potential, the neuron undergoes a rapid and transient depolarization phase. This depolarization is caused by the opening of voltage-gated sodium channels, allowing the influx of sodium ions into the cell. This rapid depolarization is the key characteristic of an action potential.
Therefore, the correct answer is option C: Rapid depolarization.
Reduced permeability of potassium leak channels would affect which of the following aspects of action potentials in a neuron?- a)The time to reach maximum depolarization
- b)The activation threshold
- c)The time to reach maximum repolarization
- d)The size of the depolarization wave
Correct answer is option 'C'. Can you explain this answer?
Reduced permeability of potassium leak channels would affect which of the following aspects of action potentials in a neuron?
a)
The time to reach maximum depolarization
b)
The activation threshold
c)
The time to reach maximum repolarization
d)
The size of the depolarization wave
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Orion Classes answered |
Reduced permeability of potassium leak channels would affect the time to reach maximum repolarization in an action potential.
Potassium leak channels contribute to the resting membrane potential of a neuron by allowing a slow leakage of potassium ions out of the cell. This leakage helps maintain the negative charge inside the cell during the resting state. When an action potential is initiated, there is a rapid depolarization phase followed by repolarization, during which the membrane potential returns to its resting state.
During repolarization, potassium channels play a crucial role by opening and allowing the efflux of potassium ions out of the cell, which restores the negative membrane potential. If the permeability of potassium leak channels is reduced, it would result in a slower efflux of potassium ions, leading to a prolonged repolarization phase. This would affect the time it takes for the membrane potential to reach maximum repolarization.
Therefore, the correct answer is C. The time to reach maximum repolarization would be affected by reduced permeability of potassium leak channels.
How would action potentials be affected in a myelinated axon if nodes are far apart?- a)Action potentials might stop
- b)Action potentials would not be affected
- c)Action potentials might travel more slowly
- d)Action potentials might travel more quickly
Correct answer is option 'A'. Can you explain this answer?
How would action potentials be affected in a myelinated axon if nodes are far apart?
a)
Action potentials might stop
b)
Action potentials would not be affected
c)
Action potentials might travel more slowly
d)
Action potentials might travel more quickly
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Orion Classes answered |
If the nodes of Ranvier are far apart in a myelinated axon, the distance between the sites where action potentials are generated is increased. This can lead to a phenomenon known as "saltatory conduction," where the action potential "jumps" from one node to another. If the distance between nodes is too large, the action potential may fail to propagate along the axon, resulting in a loss of signal transmission and a potential stoppage of action potentials.
Which term describes the cell membrane potential of a neuron at rest?- a)Polarized
- b)Depolarized
- c)Hyperpolarized
- d)Repolarized
Correct answer is option 'A'. Can you explain this answer?
Which term describes the cell membrane potential of a neuron at rest?
a)
Polarized
b)
Depolarized
c)
Hyperpolarized
d)
Repolarized
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Orion Classes answered |
The term that describes the cell membrane potential of a neuron at rest is polarized. When a neuron is at rest, the inside of the neuron has a negative charge relative to the outside. This difference in charge across the cell membrane is known as the resting membrane potential, and it is maintained through the activity of ion channels and ion pumps.
Where are voltage-gated sodium channels found in greatest concentration?- a)In the axon terminals
- b)In the trigger zones
- c)In the dendrites
- d)In the nodes of Ranvier
Correct answer is option 'B'. Can you explain this answer?
Where are voltage-gated sodium channels found in greatest concentration?
a)
In the axon terminals
b)
In the trigger zones
c)
In the dendrites
d)
In the nodes of Ranvier
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Orion Classes answered |
Voltage-gated sodium channels are found in greatest concentration in the trigger zones of neurons. The trigger zones, which consist of the axon hillock and the initial segment of the axon, are responsible for generating and initiating action potentials. These areas have a high density of voltage-gated sodium channels, which are crucial for the rapid depolarization phase of an action potential.
When a graded potential reaches the trigger zone and reaches the threshold, voltage-gated sodium channels open, allowing an influx of sodium ions into the neuron. This depolarizes the membrane and generates an action potential that propagates along the axon.
While voltage-gated sodium channels are also present in other parts of the neuron, such as the axon terminals and nodes of Ranvier, their concentration is highest at the trigger zones, where the action potential is initiated. This localization ensures the efficient generation and propagation of action potentials along the axon.
Which of the following statements is false?- a)Graded potentials are always hyperpolarizing, whereas action potentials are always depolarizing.
- b)Graded potentials are proportional to the magnitude of the stimulus, whereas action potentials are “all-or-none.”
- c)Refractory periods are not associated with graded potentials, but are associated with action potentials.
- d)Graded potentials are always decremental, whereas action potentials are always non-decremental.
Correct answer is option 'A'. Can you explain this answer?
Which of the following statements is false?
a)
Graded potentials are always hyperpolarizing, whereas action potentials are always depolarizing.
b)
Graded potentials are proportional to the magnitude of the stimulus, whereas action potentials are “all-or-none.”
c)
Refractory periods are not associated with graded potentials, but are associated with action potentials.
d)
Graded potentials are always decremental, whereas action potentials are always non-decremental.
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Orion Classes answered |
Graded potentials can be either depolarizing or hyperpolarizing, depending on the specific circumstances and the type of ion channels involved. They can result in either a decrease (hyperpolarization) or an increase (depolarization) in the membrane potential.
Therefore, the correct answer is option A: Graded potentials are always hyperpolarizing, whereas action potentials are always depolarizing.
Which of the following is the correct definition of a cation?- a)A cation is an ion that cannot have a charge.
- b)A cation is an ion that can have a positive or negative charge.
- c)A cation is a positively charged ion.
- d)A cation is a negatively charged ion.
Correct answer is option 'C'. Can you explain this answer?
Which of the following is the correct definition of a cation?
a)
A cation is an ion that cannot have a charge.
b)
A cation is an ion that can have a positive or negative charge.
c)
A cation is a positively charged ion.
d)
A cation is a negatively charged ion.
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Orion Classes answered |
A cation is an ion that has a positive charge. It is formed when an atom or molecule loses one or more electrons. The loss of electrons creates an imbalance between the number of protons (positively charged particles) and electrons (negatively charged particles), resulting in a net positive charge on the ion.
Which of the following neuronal processes transmits an action potential?- a)Axon
- b)Soma
- c)Dendrite
- d)Glia
Correct answer is option 'A'. Can you explain this answer?
Which of the following neuronal processes transmits an action potential?
a)
Axon
b)
Soma
c)
Dendrite
d)
Glia
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Orion Classes answered |
An action potential is a rapid and brief electrical signal that travels along the axon of a neuron. The axon is the long, slender extension of a neuron that carries the action potential away from the cell body (soma) towards the axon terminals, where it can transmit the signal to other neurons or target cells. The specialized properties of the axon, including its myelin sheath and nodes of Ranvier, enable efficient and rapid transmission of action potentials along its length.
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