Introduction to Physiology Lecture 3
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Questions and Answers

What does a threshold potential of -55mV indicate?

  • The nerve's membrane is at rest
  • Stimulus is too weak to open voltage-gated channels
  • The nerve is fully depolarized
  • A full action potential will occur (correct)

Which statement correctly describes the all-or-nothing principle?

  • Different nerves can have different action potential sizes
  • All action potentials for a given nerve are the same size (correct)
  • Action potentials only occur in response to subthreshold stimuli
  • Action potentials vary in size depending on the strength of the stimulus

In neuronal activity, what occurs during the refractory period?

  • The neuron cannot fire another action potential regardless of stimulus strength
  • The neuron can easily fire another action potential
  • The neuron is hyperpolarized and can only respond to strong stimuli (correct)
  • The neuron is fully depolarized

How do local potentials differ from action potentials?

<p>Local potentials reflect the shape and size of the stimulus, while action potentials do not (B)</p> Signup and view all the answers

What is the result when a stimulus exceeds the threshold potential?

<p>An action potential occurs (C)</p> Signup and view all the answers

If two stimuli both exceed the threshold, what happens according to the all-or-nothing law?

<p>Only one action potential will occur regardless of stimulus strength (A)</p> Signup and view all the answers

What occurs if a stimulus is below the threshold?

<p>The neuron will exhibit graded depolarization (D)</p> Signup and view all the answers

What happens when sodium ions (Na+) enter a neuron?

<p>It triggers the generation of an action potential (D)</p> Signup and view all the answers

What is the main event that occurs during depolarization of an action potential?

<p>Na+ entry into the neuron (B)</p> Signup and view all the answers

Which phase of an action potential is characterized by the return of the membrane potential to resting levels?

<p>Repolarization (A)</p> Signup and view all the answers

What is the threshold for initiating an action potential as indicated in the content?

<p>-55 mV (D)</p> Signup and view all the answers

Which ion channel is primarily responsible for repolarization in an action potential?

<p>Voltage-gated K+ channels (A)</p> Signup and view all the answers

What describes the phenomenon when an action potential overshoots the resting membrane potential?

<p>Hyperpolarization (C)</p> Signup and view all the answers

What phenomenon explains why changes in membrane potential decrease as you measure further from the stimulation electrode?

<p>Passive properties (A)</p> Signup and view all the answers

What mechanism indicates that local potentials can trigger action potentials?

<p>A substantial depolarizing stimulus (D)</p> Signup and view all the answers

During which phase of an action potential do voltage-gated Na+ channels primarily operate?

<p>Depolarization (C)</p> Signup and view all the answers

What is the process called that describes the change from a negative to positive membrane potential?

<p>Depolarization (A)</p> Signup and view all the answers

Which area of the neuron is primarily responsible for integrating signals and generating action potentials?

<p>Trigger Zone (D)</p> Signup and view all the answers

Flashcards

Action Potential (AP)

A rapid, short-lasting change in membrane potential that travels along the axon of a neuron, transmitting signals from one neuron to another.

Passive Properties

The electrical properties of a neuron that result from the flow of ions through the membrane, without any active involvement of ion channels.

Active Properties

The electrical properties of a neuron that are influenced by the opening and closing of ion channels, which control the movement of ions across the membrane.

Depolarization

The process where the membrane potential becomes less negative, moving closer to zero.

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Repolarization

The process where the membrane potential returns to its resting state after depolarization, becoming more negative again.

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Hyperpolarization

The state where the membrane potential becomes more negative than the resting membrane potential, often following repolarization.

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Threshold

The minimum level of depolarization required to trigger an action potential.

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Voltage-gated Na+ Channels

Ion channels that open in response to changes in membrane potential, allowing sodium ions (Na+) to flow into the cell during depolarization.

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Voltage-gated K+ Channels

Ion channels that open in response to changes in membrane potential, allowing potassium ions (K+) to flow out of the cell during repolarization.

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Trigger Zone

A specialized region of the neuron, typically located at the axon hillock, where action potentials are initiated.

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What is the threshold potential?

The membrane potential at which voltage-gated channels open, leading to an action potential. It's a specific voltage that triggers a nerve impulse.

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What does 'all-or-nothing' mean in relation to action potentials?

An action potential will either occur with full intensity or not at all. The strength of the stimulus does not influence the amplitude of the action potential.

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How do we code for different stimuli if action potentials are all-or-nothing?

The frequency of action potentials, or how rapidly they fire, encodes the strength of the stimulus. A stronger stimulus will trigger more frequent action potentials.

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What is the purpose of regeneration in action potentials?

Regeneration ensures that the action potential maintains its strength along the length of the axon. The signal is constantly re-amplified to prevent weakening.

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How does membrane potential change during an action potential?

The membrane potential reverses polarity during an action potential. Initially it's negative inside the cell, but during the action potential, the inside becomes positive.

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What is the refractory period in action potentials?

A period of time after an action potential when another action potential cannot be generated. It ensures that the action potential travels in one direction and limits the firing rate.

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What is the difference between local potentials and action potentials?

Local potentials are graded, meaning their strength varies based on the stimulus. Action potentials are all-or-nothing, with a uniform strength.

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What is the role of Na+ entry in action potentials?

Sodium ions (Na+) entering the cell through voltage-gated channels cause depolarization, which triggers the action potential.

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Study Notes

Course Information

  • Course: MD137
  • Course title: Introduction to Physiology
  • Lecturer: Leo Quinlan
  • Lecturer email: [email protected]
  • Academic year: 2024-2025

Lecture 3: Action Potentials

  • Topic: Action potentials (AP)
  • Subtopic: Neural Signaling
  • Learning Outcomes:
    • Define action potential
    • Detail the main ion movements during AP formation
    • Explain the role of ion channels and the concept of threshold
    • Describe the kinetics of an AP
    • Students are encouraged to think positively about action potentials

### Polarization States of the Membrane

  • Action potentials are represented by changes in membrane potential difference (Vm).
  • Depolarization occurs when the membrane potential becomes less negative.
  • Repolarization occurs when the membrane potential returns to its resting state.
  • Hyperpolarization occurs when the membrane potential becomes more negative than the resting potential.
  • The voltage, measured in milivolts (mV), changes during these phases.

Passive Properties

  • Henry and Huxley discovered that the membrane potential responds to stimulation, but its response decreases as the electrode is moved further from the stimulation site.
  • These properties characterize passive signal transmission in a neuron.

Active Properties

  • A small depolarizing stimulus (e.g., -65mV) produces a local potential change.
  • Stimulus recordings are measured at different locations (e.g.,REC 1, REC 2, REC 3).
  • Increasing the depolarizing stimulus (e.g., -60mV, -55mV, -40mV) causes action potentials to emerge at different recording locations.
  • As the stimulus is increased, propagation of the stimulus leads to an increasing frequency of action potentials.
  • Local potentials are graded potentials.

Generating Action Potentials

  • The threshold potential is -55 mV
  • Stimulus initiating the action potential at the trigger zone.
  • Action potentials are characterized by depolarization, repolarization, and recovery (resting state with refractory period).

Phases of Action Potentials (AP)

  • Depolarization: Voltage-gated Na+ channels open, Na+ ions enter the cell.
  • Repolarization: Voltage-gated Na+ channels close, and K+ channels open, K+ ions leave the cell.
  • Hyperpolarization: K+ channels stay open for a brief period, leading to membrane potential becoming more negative than resting potential.

Ion Channel Inaction During APs

  • Voltage-gated Na+ and K+ channels are crucial for action potential generation.
  • Na+ channels open rapidly, leading to depolarization.
  • Na+ channels inactivate, stopping further Na+ influx.
  • K+ channels open, leading to repolarization and hyperpolarization.

All-or-Nothing Principle

  • The amplitude of action potentials is consistent for a given neuron.
  • Action potentials are "all-or-none," meaning that either an action potential is initiated or it isn't, with no in-between values.

Regeneration of Action Potentials

  • Action potentials regenerate along the length of the axon.
  • The signal does not diminish as it propagates down the axon.

Membrane Potential Reversal During Action Potentials

  • During depolarization, the inside of the axon becomes positive relative to the outside.
  • Reversal in the membrane potential occurs due to ion movement across the membrane.

Refractory Period

  • Absolute refractory period: The neuron cannot generate another action potential because sodium channels are inactivated.
  • Relative refractory period: The neuron can generate another action potential, but a larger-than-normal stimulus is needed.

Different Action Potential Times

  • The duration of an action potential varies depending on the type of neuron (e.g., cardiac muscle, skeletal, motoneuron).

Local/Graded Potentials Vs Action Potentials

  • Local/Graded potentials:
    • Vary in size and shape according to the stimulus.
    • Decrease as they move away from the stimulus site.
  • Action potentials:
    • Uniform in size, shape.
    • Regenerated along the axon, without decreasing in size or magnitude.

Learning Outcomes (Recap)

  • Students should understand action potential characteristics.
    • Definition
    • Ion movements
    • Role of ion channels
    • Kinetics

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Related Documents

University of Galway Physiology Lecture 3 on Action Potentials 2024-2025 PDF

Description

This quiz covers Lecture 3 on Action Potentials from the Introduction to Physiology course. It focuses on the definitions, mechanisms, and the electrical changes involved in neural signaling and membrane polarization. Students will explore the ion movements during action potential formation and the significance of threshold levels.

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