Neuroscience: Action Potentials and Membrane Potential

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Questions and Answers

What part of a neuron is primarily responsible for receiving information?

Soma

Axon

Dendrites (correct)

Myelin sheath

Which ion has a higher concentration outside a neuron compared to its inside at resting potential?

Potassium

Sodium (correct)

Calcium

Chloride

What is the term used to describe the difference in electrical potential across a membrane?

Electrical gradient

Electrochemical gradient (correct)

Concentration gradient

Resting potential

What type of ion channel opens in response to changes in membrane potential?

Voltage-gated ion channels Signup and view all the answers

During the absolute refractory period, what is the status of the neuron?

It cannot initiate another action potential regardless of stimulus strength. Signup and view all the answers

How does the sodium-potassium exchange pump contribute to neuron function?

It maintains the electrochemical gradient. Signup and view all the answers

What event occurs first when an action potential is generated?

Threshold potential is reached Signup and view all the answers

What type of conduction does myelinated axons use for impulse propagation?

Saltatory conduction Signup and view all the answers

What initiates the cycle of depolarization during an action potential?

Depolarization reaching threshold voltage Signup and view all the answers

Which statement accurately describes the all-or-none phenomenon?

Once initiated, the action potential either occurs completely or not at all Signup and view all the answers

What role do sodium-potassium pumps play after an action potential?

They restore ionic conditions in the axon Signup and view all the answers

How does the propagation of an action potential occur?

By repeating the depolarization process at each segment of the membrane Signup and view all the answers

Why can an action potential only propagate in a forward direction?

The sodium channels at the origin are inactivated Signup and view all the answers

What occurs to the membrane's potential when depolarization reaches the threshold?

Na+ influx begins to exceed K+ efflux Signup and view all the answers

What is the primary difference between the propagation in myelinated and nonmyelinated axons?

Myelinated axons skip segments during propagation Signup and view all the answers

What must occur for an axon to fire an action potential?

Depolarization must reach a specific threshold Signup and view all the answers

What is the primary function of the axon in a neuron?

Impulse generating and conducting region Signup and view all the answers

What type of movement does anterograde transportation refer to?

Movement away from the cell body Signup and view all the answers

What does Ohm's law describe?

The relationship between voltage, current, and resistance Signup and view all the answers

What is the role of leakage channels in the neuronal membrane?

They are always open for ion passage. Signup and view all the answers

What is the term for the potential energy generated by separated charges?

Voltage Signup and view all the answers

Which type of ion channel opens in response to chemical binding?

Chemically gated channels Signup and view all the answers

Which statement about membrane potentials in neurons is correct?

Neurons can rapidly change their resting membrane potential. Signup and view all the answers

What does retrograde transportation in a neuron primarily involve?

Transporting organelles to be degraded Signup and view all the answers

How does an increase in resistance affect current flow according to Ohm's law?

Current decreases with increased resistance. Signup and view all the answers

What is the function of the Schmidt cell in neuronal anatomy?

To generate myelin sheath Signup and view all the answers

What occurs during hyperpolarization of the membrane?

The inside of the membrane becomes more negative than resting potential. Signup and view all the answers

Which of the following correctly describes graded potentials?

They result from the opening of gated ion channels. Signup and view all the answers

How do graded potentials differ from action potentials?

Action potentials involve a change in voltage of approximately 100 mV. Signup and view all the answers

Which type of graded potential occurs in sensory neurons?

Receptor potential. Signup and view all the answers

What is true about the flow of current in graded potentials?

Current dissipates quickly and decays. Signup and view all the answers

Which statement about action potentials is correct?

They occur only in muscle cells and axons of neurons. Signup and view all the answers

What initiates the depolarization in graded potentials?

Binding of neurotransmitters to receptors. Signup and view all the answers

What effect does increased stimulus strength have on graded potentials?

It increases both voltage change and current flow distance. Signup and view all the answers

What determines the difference between a weak stimulus and a strong one in the nervous system?

Frequency of impulses received per second Signup and view all the answers

Which type of refractory period allows for the possibility of a second action potential under certain conditions?

Relative refractory period Signup and view all the answers

What is the primary factor influencing the conduction velocity of action potentials in axons?

Axon diameter Signup and view all the answers

Which statement is true regarding the absolute refractory period?

A neuron cannot trigger another action potential during this period Signup and view all the answers

How are larger-diameter axons advantageous for action potential conduction?

They have faster impulse conduction due to less resistance Signup and view all the answers

Study Notes

Action Potential

Neurons are highly excitable and can rapidly change resting membrane potential
Action potentials (APs) are the primary mechanism for long-distance neural communication.
APs only occur in muscle cells and axons of neurons
APs are brief reversals of membrane potential with a voltage change of approximately 100 mV.
APs do not decay over distance like graded potentials do
APs involve the opening of specific voltage-gated channels

Resting Membrane Potential

All cells have a resting membrane potential.
Neurons can quickly change their resting membrane potential.

Threshold and the All-or-None Phenomenon

Not all depolarization events produce APs
For an axon to "fire," depolarization must reach a threshold voltage, which triggers the AP.
Threshold is characterized by:
- Membrane depolarization by 15 to 20 mV.
- Increased Na+ permeability.
- Na+ influx surpasses K+ efflux.
- Initiation of the positive feedback loop.
All-or-None Principle: an AP either occurs completely or not at all.

Propagation of an Action Potential

Propagation facilitates the transmission of APs from their origin down the entire axon length towards terminals.
Na+ influx through voltage gates in one membrane area leads to local currents, which open Na+ voltage gates in nearby membrane areas
This causes depolarization in that area, which in turn causes depolarization in the adjacent area.
Once initiated, an AP is self-propagating.
- In non-myelinated axons, each segment of membrane depolarizes then repolarizes
- Propagation in myelinated axons differs
- Since Na+ channels closer to the AP origin are still inactivated, no new AP is generated there.
The AP occurs only in a forward direction.

Coding for Stimulus Intensity

All APs are alike and are independent of stimulus intensity.
The CNS distinguishes between weak and strong stimuli by the frequency of impulses, which is the number of impulses (APs) received per second.
Higher frequencies indicate stronger stimuli.

Refractory Periods

Refractory period is the period during which a neuron cannot trigger another AP. - Voltage-gated Na+ channels are open, preventing the neuron from responding to another stimulus, regardless of strength or frequency.
Absolute Refractory Period: another AP is not possible until the reset of the VG Na+ channels.
- Enforces the All-or-None Principle
Relative Refractory Period: follows the absolute refractory period, most Na+ channels are already reset.
- Coincides with repolarization.

Conduction Velocity

APs only occur in axons, not other cell areas.
AP conduction velocities in axons vary widely.
Rate of AP propagation depends on:
- Axon Diameter: larger-diameter fibers have less resistance to local current flow, which leads to faster impulse conduction.
- Myelination: myelinated axons exhibit saltatory conduction, increasing conduction velocity.

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Description

This quiz covers the fundamental concepts of action potentials and resting membrane potential in neurons. It includes details about the all-or-none phenomenon, the importance of voltage-gated channels, and how depolarization affects neural communication. Test your understanding of these crucial topics in neuroscience.