Membranes and Receptors: Action Potentials

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What triggers the opening of Na+ channels during the action potential?

Increased K+ concentration

A decrease in membrane potential

Reaching the threshold potential (correct)

Hyperpolarization of the membrane

During the action potential, what occurs immediately after the Na+ channels open?

The membrane undergoes hyperpolarization

K+ channels begin to close

The membrane depolarizes due to Na+ influx (correct)

The Na+/K+ transporter activates instantly

What is the primary reason for the refractory period following an action potential?

Increased permeability to Na+ ions

Ongoing K+ efflux (correct)

A change in extracellular potassium levels

Closure of Na+ channels

Which of the following statements accurately describes the all-or-none law of action potentials?

Action potentials occur fully or not at all, depending on reaching the threshold Signup and view all the answers

What is the result of K+ ions leaving the cell during repolarization?

The membrane hyperpolarizes beyond the resting potential Signup and view all the answers

What role does the Na+/K+ transporter play after an action potential?

It helps restore the resting potential of the membrane Signup and view all the answers

How does the concentration of sodium ions in the external fluid influence the action potential?

It greatly influences the generation of action potentials Signup and view all the answers

What causes the membrane potential to become more negative during the action potential?

Efflux of K+ ions Signup and view all the answers

What is the main purpose of the plateau phase in cardiac muscle action potentials?

To allow for a prolonged contraction crucial for blood expulsion. Signup and view all the answers

Which correctly describes the absolute refractory period (ARP) during cardiac action potentials?

Most Na+ channels are inactivated and cannot reopen. Signup and view all the answers

What event occurs during the repolarization phase of an action potential?

K+ channels activate, leading to the decrease of membrane potential. Signup and view all the answers

How does the absolute refractory period in cardiac muscle compare to that in skeletal muscle?

It is longer to prevent tetanus and summation. Signup and view all the answers

What primarily causes the depolarization phase of the cardiac action potential?

Rapid influx of Na+ ions through channels. Signup and view all the answers

What is the role of the Na+/K+ pump during an action potential?

It is not involved in the action potential's repolarization. Signup and view all the answers

Which statement is true regarding the recovery of Na+ channels after an action potential?

They recover only once the membrane returns to resting potential. Signup and view all the answers

What is the nature of voltage-gated ion channels?

They are transmembrane proteins responding to membrane potential changes. Signup and view all the answers

Study Notes

Membranes and Receptors: Electrical Excitability

The lecture covers action potentials and their properties.
Students will be able to identify the properties of action potentials and their ionic basis.
They will outline changes in membrane ionic permeability.
Students will describe the all-or-none law and refractoriness.
They will demonstrate some properties of ion channels.
Application of these facts to local anesthetics will be covered.

Action Potential (AP)

Action potentials are changes in membrane voltage.
They are nerve impulses and are not graded.
Once initiated, they affect the entire excitable membrane.
They propagate along axon surfaces.
Membrane potential is the voltage difference across a cell membrane, where the cytoplasm is more negative than the exterior.

Voltage-Dependent Sodium and Potassium Channels

These channels have specific stages.
The first stage of the sodium channel includes activation.
The second stage of the sodium channel is inactivation.
The potassium channels open and the sodium channels close at the peak of the action potential.
The channels then begin to reset.

Action Potential (AP) Steps

A stimulus from a sensory cell or neuron depolarizes the target cell to threshold potential.
If threshold is reached, sodium channels open and the membrane depolarizes.
At peak action potential, potassium channels open, allowing potassium to leave the cell.
Simultaneously, sodium channels close.
The membrane hyperpolarizes as more K+ leaves.
The membrane enters a refractory period, unable to fire.
Potassium channels close, and the Na+/K+ transporter restores resting potential.

Action Potential Generation

Action potentials are driven by changes in membrane permeability to sodium, bringing the membrane closer to the sodium equilibrium potential.
The sodium hypothesis of action potentials describes this.
The concentration of sodium ions in the external fluid greatly influences action potential.

Effects of Membrane Potential Changes

Changes in membrane potential impact sodium and potassium currents.
This effect is demonstrated graphically.

Resting Potential

The resting potential is 65 mV.
It's maintained by K+ leak channels and limited Na+ leak channels.
The inside of the cell is more negatively charged than the outside.

Recovery After Action Potential

After an action potential, most sodium channels are inactivated.
They need time to recover before opening again—this process occurs when membrane potential returns to its resting level.
The absolute refractory period is when all Na+ channels are inactivated, and the relative refractory period occurs as channels recover.

Action Potential Steps Summary

Depolarization to threshold activates sodium channels.
Sodium influx causes further depolarization.
Potassium channels open, repolarizing the membrane.
The membrane hyperpolarizes slightly before returning to resting potential.

Molecular Nature of Voltage-Gated Channels

Voltage-gated ion channels are trans-membrane proteins.
Channel function is regulated by changes in the membrane potential.
Opening/closing is triggered by changes in ion concentration and charge gradient.

Types of Ion Channels

Voltage-gated ion channels respond to voltage changes.
Ligand-gated ion channels (activated by ligands).
Mechanically-gated ion channels, responding to mechanical forces.

Voltage-Gated Ion Channel Structure

The structure includes homologous repeats of transmembrane spanning domains.
Some domains are responsive to the voltage field across the membrane.
This is important for the function of Na+ and Ca++ channels.

Additional Notes

The voltage-gated ion channels are regulated by the changes in the membrane potential, near the channel.
Voltage-gated ion channels are important in maintaining neuronal homeostasis, secretion, endocytosis, muscle contraction, synaptic transmission, ciliary control, fertilization, etc.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the properties of action potentials and their ionic basis, delving into changes in membrane ionic permeability. It covers important concepts such as the all-or-none law, refractoriness, and the functionality of voltage-dependent sodium and potassium channels, as well as their applications in local anesthetics.