Neurophysiology Study Guide – Action Potentials, Synaptic Transmission, and Nerve Fiber Properties

Q1. What type of conduction takes place in unmyelinated axons?

Background

Topic: Action Potential Propagation

This question tests your understanding of how action potentials travel along axons without myelin.

Key Terms

• Unmyelinated axon: An axon lacking a myelin sheath.

• Continuous conduction: The process by which action potentials propagate along every segment of the axon membrane.

Step-by-Step Guidance

1. Recall that myelin sheaths allow for saltatory conduction, where action potentials "jump" between nodes of Ranvier.

2. In the absence of myelin, consider how the action potential must be regenerated at each segment of the axon.

3. Think about the speed and efficiency differences between myelinated and unmyelinated axons.

Try solving on your own before revealing the answer!

Q2. Why is an action potential self-regenerating?

Background

Topic: Action Potential Propagation

This question examines why an action potential continues to move along the axon without fading.

Key Terms

• Depolarizing current: Movement of positive ions (like Na+) that makes the inside of the cell less negative.

• Threshold: The membrane potential at which voltage-gated channels open to initiate an action potential.

Step-by-Step Guidance

1. Consider what happens when Na+ channels open during an action potential.

2. Think about how the influx of Na+ affects adjacent regions of the axon membrane.

3. Relate this to the concept of local currents and how they bring neighboring segments to threshold.

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Q3. Why does regeneration of the action potential occur in one direction, rather than in two directions?

Background

Topic: Action Potential Directionality

This question tests your understanding of the refractory period and how it ensures unidirectional propagation of action potentials.

Key Terms

• Refractory period: The time after an action potential when a neuron cannot fire another action potential.

• Inactivation gate: Part of the voltage-gated Na+ channel that closes after activation, preventing further Na+ influx.

Step-by-Step Guidance

1. Recall what happens to voltage-gated Na+ channels immediately after they open.

2. Think about how the inactivation of these channels affects the ability of the membrane to generate another action potential.

3. Consider why this mechanism prevents the action potential from moving backward.

Try solving on your own before revealing the answer!

Q4. What is the function of the myelin sheath?

Background

Topic: Myelination and Nerve Conduction

This question focuses on the role of myelin in nervous system function.

Key Terms

• Myelin sheath: A fatty layer that wraps around axons, produced by glial cells.

• Conduction velocity: The speed at which an action potential travels along an axon.

Step-by-Step Guidance

1. Recall how myelin affects the electrical properties of the axon membrane.

2. Think about how myelin changes the way action potentials propagate (compare to unmyelinated axons).

3. Consider the importance of nodes of Ranvier in myelinated axons.

Try solving on your own before revealing the answer!

Q5. What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?

Background

Topic: Action Potential Phases

This question tests your knowledge of the sequence of channel openings and closings during an action potential.

Key Terms

• Voltage-gated Na+ channel: Opens rapidly in response to depolarization, then inactivates.

• Voltage-gated K+ channel: Opens more slowly in response to depolarization.

Step-by-Step Guidance

1. Recall the sequence of events during the depolarization and repolarization phases.

2. At the peak of depolarization, consider what happens to the Na+ channel inactivation gate.

3. Think about when K+ channels open and how this affects the membrane potential.

Try solving on your own before revealing the answer!

Q6. In which type of axon will velocity of action potential conduction be the fastest?

Background

Topic: Nerve Fiber Types and Conduction Velocity

This question examines the factors that influence how quickly action potentials travel along axons.

Key Terms

• Myelinated axon: Axon covered with myelin sheath.

• Axon diameter: Larger diameter reduces resistance and increases conduction speed.

Step-by-Step Guidance

1. Recall the relationship between myelination and conduction speed.

2. Consider how axon diameter affects the speed of action potential propagation.

3. Think about which combination (myelinated/unmyelinated, large/small diameter) would be fastest.

Try solving on your own before revealing the answer!

Q7. Where in the neuron is an action potential initially generated?

Background

Topic: Neuronal Structure and Function

This question tests your understanding of where action potentials begin in a neuron.

Key Terms

• Axon hillock: The region where the axon joins the cell body.

• Initial segment: The first part of the axon, just after the axon hillock.

Step-by-Step Guidance

1. Recall the structure of a typical neuron (dendrites, soma, axon hillock, axon).

2. Think about where voltage-gated Na+ channels are most densely clustered.

3. Consider why this region is the site of action potential initiation.

Try solving on your own before revealing the answer!

Q8. The depolarization phase of an action potential results from the opening of which channels?

Background

Topic: Action Potential Phases

This question focuses on the ionic basis of the depolarization phase.

Key Terms

• Depolarization: The process by which the membrane potential becomes less negative (more positive).

• Voltage-gated Na+ channels: Channels that open in response to depolarization, allowing Na+ influx.

Step-by-Step Guidance

1. Recall which ions are involved in depolarizing the membrane.

2. Think about which channels open first during an action potential.

3. Consider the direction of ion movement and its effect on membrane potential.

Try solving on your own before revealing the answer!

Q9. The repolarization phase of an action potential results from __________.

Background

Topic: Action Potential Phases

This question tests your understanding of how the neuron returns to its resting potential after depolarization.

Key Terms

• Repolarization: The process of returning the membrane potential to a more negative value after depolarization.

• Voltage-gated K+ channels: Channels that open to allow K+ to exit the cell.

Step-by-Step Guidance

1. Recall the sequence of channel openings during an action potential.

2. Think about which ion movement restores the negative membrane potential.

3. Consider the timing of K+ channel opening relative to Na+ channel inactivation.

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Q10. Hyperpolarization results from __________.

Background

Topic: Action Potential Phases

This question examines why the membrane potential temporarily becomes more negative than the resting potential after an action potential.

Key Terms

• Hyperpolarization: The membrane potential becomes more negative than the resting potential.

• Voltage-gated K+ channels: Their slow closing can cause excess K+ to leave the cell.

Step-by-Step Guidance

1. Recall what happens to K+ channels after repolarization.

2. Think about how the timing of channel closing affects membrane potential.

3. Consider the consequences of prolonged K+ efflux.

Try solving on your own before revealing the answer!