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Questions and Answers
A nerve impulse is a physicochemical disturbance produced by a stimulus of any intensity.
A nerve impulse is a physicochemical disturbance produced by a stimulus of any intensity.
False (B)
The latent period represents the time consumed for the impulse to propagate from the stimulating electrode to the recording electrode.
The latent period represents the time consumed for the impulse to propagate from the stimulating electrode to the recording electrode.
True (A)
The firing level in a nerve is a membrane potential of -70 mV.
The firing level in a nerve is a membrane potential of -70 mV.
False (B)
The spike potential refers to the gradual repolarization of a neuron.
The spike potential refers to the gradual repolarization of a neuron.
After hyperpolarization, the membrane potential overshoots in the direction of depolarization.
After hyperpolarization, the membrane potential overshoots in the direction of depolarization.
Voltage-gated potassium channels open quickly compared to voltage-gated sodium channels.
Voltage-gated potassium channels open quickly compared to voltage-gated sodium channels.
The Na+-K+ pump helps restore the normal ionic distribution after a nerve impulse.
The Na+-K+ pump helps restore the normal ionic distribution after a nerve impulse.
The spike potential includes an influx of K+ ions during depolarization.
The spike potential includes an influx of K+ ions during depolarization.
During the Absolute Refractory Period, excitability is completely lost.
During the Absolute Refractory Period, excitability is completely lost.
The Relative Refractory Period corresponds to a state of excitability that is above normal.
The Relative Refractory Period corresponds to a state of excitability that is above normal.
Subthreshold stimuli can produce a response during the Supernormal Phase of Excitability.
Subthreshold stimuli can produce a response during the Supernormal Phase of Excitability.
In the Subnormal Phase of Excitability, less than the normal threshold stimulus is needed to trigger an action potential.
In the Subnormal Phase of Excitability, less than the normal threshold stimulus is needed to trigger an action potential.
The firing level is defined as the membrane potential that is -55 mV in the nerve.
The firing level is defined as the membrane potential that is -55 mV in the nerve.
The supernormal phase of excitability occurs during the last 30% of repolarization.
The supernormal phase of excitability occurs during the last 30% of repolarization.
The latent period represents the immediate response time after a stimulus is applied.
The latent period represents the immediate response time after a stimulus is applied.
Excitability during the Subnormal Phase is high and easily triggered.
Excitability during the Subnormal Phase is high and easily triggered.
Warming and alkalinity decrease nerve excitability.
Warming and alkalinity decrease nerve excitability.
The spike potential is characterized by rapid depolarization followed by rapid repolarization.
The spike potential is characterized by rapid depolarization followed by rapid repolarization.
Low calcium concentration in the extracellular fluid increases Na+ permeability and thus increases excitability.
Low calcium concentration in the extracellular fluid increases Na+ permeability and thus increases excitability.
High potassium concentration in the extracellular fluid increases the resting membrane potential (RMP).
High potassium concentration in the extracellular fluid increases the resting membrane potential (RMP).
Local anesthetics like cocaine work by increasing the permeability of the nerve membrane to Na+.
Local anesthetics like cocaine work by increasing the permeability of the nerve membrane to Na+.
Cooling and oxygen lack decrease nerve excitability.
Cooling and oxygen lack decrease nerve excitability.
The subnormal phase of excitability requires a stronger stimulus than normal to provoke a response.
The subnormal phase of excitability requires a stronger stimulus than normal to provoke a response.
In an acidic medium, ionization of calcium decreases, which can negatively affect nerve excitability.
In an acidic medium, ionization of calcium decreases, which can negatively affect nerve excitability.
Flashcards
Nerve Impulse
Nerve Impulse
A physicochemical disturbance that travels along a nerve fiber caused by a stimulus of sufficient strength (threshold intensity). It involves electrical, excitability, metabolic, and thermal changes.
Latent Period
Latent Period
A period during which the membrane potential remains unchanged after a stimulus is applied.
Spike Potential
Spike Potential
The rapid increase in membrane potential (depolarization) followed by a rapid decrease (repolarization), forming the characteristic shape of the nerve impulse.
Firing Level
Firing Level
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After Hyperpolarization
After Hyperpolarization
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Depolarization
Depolarization
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Repolarization
Repolarization
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Ionic Restoration
Ionic Restoration
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Absolute Refractory Period
Absolute Refractory Period
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Relative Refractory Period
Relative Refractory Period
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Supernormal Phase of Excitability
Supernormal Phase of Excitability
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Subnormal Phase of Excitability
Subnormal Phase of Excitability
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Factors Increasing Nerve Excitability
Factors Increasing Nerve Excitability
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Factors Decreasing Nerve Excitability
Factors Decreasing Nerve Excitability
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Effect of High Extracellular K+ on Excitability
Effect of High Extracellular K+ on Excitability
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Effect of Low Extracellular Ca++ on Excitability
Effect of Low Extracellular Ca++ on Excitability
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Effect of Local Anesthetics on Excitability
Effect of Local Anesthetics on Excitability
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Study Notes
Nerve Impulse
- A physicochemical disturbance initiated by a stimulus of threshold intensity or more.
- Propagated as a wave along the nerve fiber.
- Accompanied by:
- Electric changes (action potential)
- Excitability changes
- Metabolic changes
- Thermal changes
Structure of the Neuron
- Cell body
- Axon
- Telodendria
- Axon hillock
- Synaptic terminals
- Dendritic branches
- Nucleus
- Endoplasmic reticulum
- Golgi apparatus
- Mitochondria
Membrane Potential (Leakage of Potassium)
- Potassium leaks from inside the nerve membrane to the outside.
- This leakage is facilitated by potassium leak channels.
- Potassium ions move down their concentration gradient.
- The sodium-potassium pump regulates potassium and sodium concentrations.
Nerve Impulse - Electric Changes
- Stimulus Artifact (SA): Current leakage from the stimulating electrode to the recording electrode.
- Latent Period (LP): Isopotential period following the stimulus artifact, representing the time taken for the impulse to travel between electrodes.
- Velocity of conduction (V) = distance (d) / time (t).
Stages of the Action Potential
- Resting (Polarized) Stage: Membrane potential at rest (-70 mV).
- Depolarization Stage: Rapid change in membrane potential to +35 mV, due to sodium influx.
- Repolarization Stage: Return to negative values, caused by potassium efflux.
- Hyperpolarization Stage: Brief dip below resting potential, due to continued potassium efflux.
The Spike Potential
- Depolarization: Opening of voltage-gated sodium channels; sodium influx; membrane potential (-70mV) to (-55mV) to +35 mV.
- Firing Level (FL): Membrane potential (-55 mV) at which the depolarization rate shifts from gradual to rapid.
- Repolarization: Maximum opening of voltage-gated potassium channels; potassium outflux; return of membrane potential to its resting value.
Excitability Changes During the Action Potential
- Absolute Refractory Period: Excitability is completely lost during the ascending and early descending phase of the action potential.
- Relative Refractory Period: Excitability starts returning to normal but is still below normal. Occurs in the last two-thirds of the descending phase.
- Supernormal Phase: Excitability is greater than normal; subthreshold stimuli can produce a response. Corresponds to 30% of repolarization.
- Subnormal Phase: Excitability is less than normal; a stronger stimulus is required. Corresponds to the after-hyperpolarization phase.
Factors Increasing Nerve Excitability
- Warming
- Alkalinity
- High extracellular potassium concentration
- Low extracellular calcium concentration
Factors Decreasing Nerve Excitability
- Local anesthetics (e.g., cocaine)
- Low extracellular potassium
- High extracellular calcium
- Cooling
- Reduced blood supply
- Lack of oxygen
- Acidity
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