Physiology MD137 Lecture 3: Action Potentials

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Questions and Answers

What is the threshold potential required to trigger an action potential?

-90mV

+30mV

-55mV (correct)

0mV

Which statement accurately describes an action potential according to the all-or-nothing principle?

Action potentials vary in size depending on the strength of the stimulus.

There are both large and small action potentials.

All action potentials for a given nerve appear uniform. (correct)

Action potentials can be graded based on stimulus intensity.

What happens to the membrane potential when it surpasses the threshold?

It equalizes the internal and external potentials.

It causes a reversal in the local potential.

It results in the opening of voltage-gated channels. (correct)

It leads to a hyperpolarization of the neuron.

What is the primary difference between local potentials and action potentials?

Local potentials reflect the size of the stimulus, while action potentials do not. Signup and view all the answers

What is a characteristic of the refractory period after an action potential?

The neuron is less sensitive to new stimuli. Signup and view all the answers

What occurs at a membrane potential of +30mV during an action potential?

Voltage-gated sodium channels are inactivated. Signup and view all the answers

What defines subthreshold stimuli in relation to action potentials?

They do not trigger an action potential. Signup and view all the answers

How does the strength of a stimulus relate to action potentials?

Stimuli strength is irrelevant once the threshold is met. Signup and view all the answers

What is the initial phase of an action potential characterized by Na+ entry called?

Depolarization Signup and view all the answers

Which ion channel is predominantly involved during repolarization of an action potential?

Voltage-gated K+ channels Signup and view all the answers

What is the membrane potential at the peak of an action potential typically around?

+40 mV Signup and view all the answers

What occurs during the hyperpolarization phase of an action potential?

K+ ions exit the neuron rapidly Signup and view all the answers

What term describes the minimum membrane potential required to trigger an action potential?

Threshold Signup and view all the answers

Where in a neuron is the action potential typically generated?

Axon Hillock Signup and view all the answers

Which phase of the action potential involves a rapid change in membrane potential from -70 mV to +40 mV?

Depolarization Signup and view all the answers

In what manner does the membrane potential change as it moves further from the stimulus site during passive signaling?

It decreases exponentially Signup and view all the answers

Which of the following describes the resting membrane potential of a neuron?

-70 mV Signup and view all the answers

What happens to the cell after an action potential is generated?

It enters a refractory period Signup and view all the answers

Study Notes

Course Information

Course: MD137
Introduction to Physiology
Lecturer: Leo Quinlan
Email: [email protected]
Year: 2024-2025

Lecture 3: Action Potentials

Action Potentials (AP)

Neural Signalling (a physiological process)

Learning Outcomes

Define Action Potential (AP)
Identify ion movements during AP formation.
Explain ion channels & the threshold value.
Describe AP kinetics.

Polarisation States of the Membrane

Depolarisation: Membrane potential decreases.
Repolarisation: Membrane potential returns to resting state.
Hyperpolarisation: Membrane potential drops below resting potential.

Passive Properties

Membrane potential changes in response to a stimulus.
Decreases with distance from stimulus.
Describes passive properties of a neuron

Active Properties

Small depolarisation stimulus (-65 mV).
Increase in depolarisation stimulus (-60 mV).
Increase in depolarisation stimulus further (-55 mV).
Increase in depolarisation stimulus further (-40 mV).
Local potentials observed with stimuli above threshold.
Generates action potentials

Generating Action Potentials

Threshold potential: -55mV (voltage below which voltage-gated channels don't open).
Stimulus initiates depolarisation.
Reaching threshold triggers a rapid change in membrane potential (AP).
Repolarisation follows the AP.
Refractory period occurs after firing an action potential.

Phases of AP

Depolarisation: Na+ entry facilitated by voltage-gated Na+ channels.
Repolarisation: K+ exit facilitated by voltage-gated K+ channels.

Phases of Action Potentials (AP)

Depolarisation: Quick, rapid increase in membrane potential.
Repolarisation: Return of membrane potential to resting state.
Hyperpolarisation: Membrane briefly drops below resting membrane potential.

All or Nothing

All action potentials for a given nerve are the same, varying on stimulus.
All or nothing law: Action potentials will only start below a particular voltage, if it is above the voltage a full action potential will form.

Regeneration

Action potential (AP) regenerated at each part of the axon.
Series of triggered action potentials down the axon.

Membrane Potential Reverses

Intracellular measurements and extracellular recordings.
Action potential reverses the inside and outside of the cell's membrane polarity.

Refractory Period

Determines how quickly neurons can respond to stimuli.
Neurons can't respond during absolute refractory period, but can during relative refractory period
Includes Absolute refractory period (all voltage gated channels have closed) and Relative refractory period (some voltage channels start to reset).

Local/Graded VS Action Potentials

Local potentials: Reflect stimulus size and strength, reducing strength over distance, initiating signal from receptor.
Action potentials: Uniform strength, same size, regenerating at each point along the axon, carrying signal long distances between neurons.

Learning Outcomes (recap)

Definition of an action potential (AP)
Key ion movements in forming AP
Explanation of ion channels & the threshold value.
Kinetics of an action potential.

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Description

This quiz covers the fundamental concepts of action potentials, including definitions, ion movements, and the kinetics involved in neural signaling. It explores the different states of membrane polarization and the passive and active properties of neurons. Test your understanding of this crucial topic in physiology!