Neurophysiology: Action Potential Dynamics
37 Questions
3 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the role of the sodium-potassium pump during the falling phase of the action potential (AP)?

  • It directly controls the opening and closing of the voltage-gated potassium channels.
  • It restores the initial concentration gradients of sodium and potassium, preparing the cell for another AP. (correct)
  • It directly contributes to the influx of sodium ions (Na+) into the cell.
  • It directly contributes to the rapid efflux of potassium ions (K+) out of the cell.

During the falling phase of the AP, why does the potassium channel remain open even after the membrane potential reaches the resting membrane potential (RMP)?

  • The potassium channel's closure is delayed due to the slow inactivation kinetics of the potassium channel. (correct)
  • The potassium channel is insensitive to changes in membrane potential.
  • The potassium channel is directly activated by the influx of sodium ions.
  • The potassium channel remains open due to the inactivation of the sodium channel, preventing further sodium influx.

Consider the role of the potassium leak channels during the rising phase of the AP. How does their activity affect the overall action potential?

  • They are primarily responsible for initiating the action potential due to their constant leakiness.
  • They contribute to a continuous outward flow of potassium, opposing and slightly slowing the depolarization phase. (correct)
  • They play a minor role, as the massive influx of sodium ions overrides their effects.
  • They contribute to the rapid inflow of potassium ions, accelerating the depolarization phase.

Which of the following statements correctly describes the inactivation of the sodium channel during the rising phase of the action potential?

<p>Sodium channel inactivation occurs because of a temporary physical block within the channel itself. (D)</p> Signup and view all the answers

What is the primary consequence of the inactivation of the sodium channels during the falling phase of the action potential?

<p>It prevents further depolarization and allows the membrane potential to return to its resting state. (C)</p> Signup and view all the answers

What is the role of calcium ions (Ca2+) in neurotransmitter release?

<p>Ca2+ ions trigger the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters. (A)</p> Signup and view all the answers

Which of the following statements accurately describes the difference between electrical and chemical synapses?

<p>Electrical synapses allow for faster transmission but cannot be modulated, while chemical synapses are slower but allow for greater flexibility. (A)</p> Signup and view all the answers

What is the primary function of a neurotransmitter receptor located on the postsynaptic membrane?

<p>To bind to neurotransmitters and initiate a signal transduction pathway, leading to changes in postsynaptic cell activity. (D)</p> Signup and view all the answers

How does the experimental research described in the text demonstrate the chemical nature of nerve impulse transmission?

<p>By showing that the solution from Heart 1 could induce the same response in Heart 2, even without direct nerve stimulation, indicating chemical transmission. (D)</p> Signup and view all the answers

What is the significance of the statement that some neurotransmitters act as "first messengers" and trigger "second messengers"?

<p>It emphasizes that some neurotransmitter signaling pathways are indirect and involve complex molecular cascades. (B)</p> Signup and view all the answers

Which of the following scenarios would directly contribute to a postsynaptic neuron becoming more likely to fire an action potential?

<p>The binding of an excitatory neurotransmitter to its receptor on the postsynaptic membrane. (B)</p> Signup and view all the answers

What does the concept of "synaptic integration" refer to?

<p>The ability of the postsynaptic neuron to combine and analyze inputs from multiple presynaptic neurons. (B)</p> Signup and view all the answers

What is the primary benefit of chemical synapses over electrical synapses, despite the slower transmission speed?

<p>Chemical synapses allow for more rapid transmission of signals over longer distances. (A)</p> Signup and view all the answers

How does the neurotransmitter acetylcholine affect cardiac muscle contraction?

<p>It binds to a metabotropic receptor, triggering a signaling cascade that indirectly inhibits contraction. (A)</p> Signup and view all the answers

Which characteristic distinguishes metabotropic receptors from ionotropic receptors?

<p>Metabotropic receptors initiate a signaling cascade with second messengers, while ionotropic receptors directly open ion channels. (B)</p> Signup and view all the answers

How is the release of neurotransmitters from the axon terminal terminated?

<p>All of the above mechanisms play a role in terminating neurotransmitter release. (D)</p> Signup and view all the answers

Which statement accurately describes the role of calcium ions in neurotransmitter release?

<p>Calcium ions trigger the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft. (C)</p> Signup and view all the answers

What is the primary function of the nicotinic acetylcholine receptor?

<p>To allow the passage of sodium ions into the postsynaptic cell, leading to depolarization and muscle contraction. (D)</p> Signup and view all the answers

How does the diversity of neurotransmitter receptors contribute to the complexity of neuronal signaling?

<p>All of the above statements correctly explain the significance of neurotransmitter receptor diversity. (D)</p> Signup and view all the answers

What is the main role of enzymes in the process of neurotransmitter removal from the synaptic cleft?

<p>Enzymes break down neurotransmitters into inactive metabolites, terminating their signaling action. (A)</p> Signup and view all the answers

Why is the binding of acetylcholine to its receptor considered ligand-gated?

<p>Acetylcholine acts as a ligand, binding to the receptor and triggering a conformational change that opens the ion channel. (D)</p> Signup and view all the answers

Which of the following statements accurately describes the role of myelin in AP conduction?

<p>Myelin allows for faster conduction velocity in the AP by reducing ion leakage across the axon membrane. (B)</p> Signup and view all the answers

What is the primary reason why the nodes of Ranvier are crucial for saltatory conduction?

<p>The high concentration of sodium and potassium ions at the nodes allows for rapid ion movement and AP regeneration. (C)</p> Signup and view all the answers

Imagine an experimental scenario where the concentration of sodium ions ($Na^+$) is reduced at the nodes of Ranvier. How would this affect saltatory conduction?

<p>Saltatory conduction would be less efficient as the AP would diminish faster between nodes. (C)</p> Signup and view all the answers

How does the structure of the axon hillock in a myelinated neuron compare to that of an unmyelinated neuron?

<p>The axon hillock in a myelinated neuron is structurally similar to that of an unmyelinated neuron. (B)</p> Signup and view all the answers

Which of the following best explains why myelinated neurons can achieve significantly higher conduction velocities compared to unmyelinated neurons?

<p>The presence of myelin decreases ion leakage across the axon membrane, leading to faster AP conduction. (C)</p> Signup and view all the answers

What is the primary difference between the conduction process in myelinated and unmyelinated neurons?

<p>Myelinated neurons exhibit saltatory conduction, while unmyelinated neurons exhibit continuous conduction. (C)</p> Signup and view all the answers

If a toxin preferentially destroyed the myelin sheaths in the peripheral nervous system, what would be the most likely consequence?

<p>Slowed conduction velocity of nerve impulses, leading to weakness or paralysis. (C)</p> Signup and view all the answers

Which of the following is NOT a characteristic feature of saltatory conduction?

<p>It is slower than continuous conduction. (A)</p> Signup and view all the answers

Why does the depolarization of the membrane during an action potential trigger the opening of more sodium channels?

<p>The depolarization causes a conformational change in the sodium channels, leading to their activation. (C)</p> Signup and view all the answers

Which of the following statements accurately describes the role of the refractory period in the propagation of action potentials?

<p>The refractory period prevents the action potential from traveling backwards, ensuring unidirectional propagation. (B)</p> Signup and view all the answers

Which of the following factors is NOT a determinant of the speed of action potential conduction in a myelinated axon?

<p>The concentration of sodium channels at the axon hillock. (B)</p> Signup and view all the answers

How do dendrites and the cell body differ from the axon in terms of their role in action potential propagation?

<p>Dendrites and the cell body have a higher concentration of potassium channels, preventing backward propagation of the action potential. (A)</p> Signup and view all the answers

Why is the action potential conducted unchanged along the axon membrane to the terminals?

<p>The action potential is actively regenerated at each segment of the axon, ensuring its strength remains constant. (C)</p> Signup and view all the answers

Which of the following statements accurately describes the action potential's behavior in an unmyelinated axon?

<p>The action potential travels along the axon in a series of discrete steps, with the signal regenerating at each step. (A)</p> Signup and view all the answers

Which of the following statements correctly compares the speed of action potential conduction in myelinated and unmyelinated axons?

<p>Action potential conduction in myelinated axons is faster because the myelin sheath prevents the leakage of ions and allows for faster regeneration of the signal at the nodes of Ranvier. (A)</p> Signup and view all the answers

Why is the diameter of an unmyelinated axon a significant factor determining the speed of action potential conduction?

<p>A larger axon diameter reduces the resistance to ion flow, allowing for faster conduction. (B)</p> Signup and view all the answers

Flashcards

Myelinated Axon

An axon surrounded by myelin sheath that increases conduction speed.

Saltatory Conduction

The process of action potentials jumping between nodes of Ranvier in myelinated axons.

Nodes of Ranvier

Small gaps in the myelin sheath where ions can cross the membrane.

Axon Hillock

The part of the neuron where action potentials are initiated, similar in both myelinated and unmyelinated neurons.

Signup and view all the flashcards

Electrical Synapse

A type of synapse where impulses pass directly through gap junctions between cells.

Signup and view all the flashcards

Chemical Synapse

A synapse where neurotransmitters are released from the presynaptic cell to the postsynaptic cell.

Signup and view all the flashcards

Presynaptic Cell

The neuron that sends the signal in a synapse.

Signup and view all the flashcards

Postsynaptic Cell

The neuron that receives the signal in a synapse.

Signup and view all the flashcards

Hodgkin-Huxley Cycle

The process of action potential rise due to positive feedback fromNa+ channel activation.

Signup and view all the flashcards

Action Potential Propagation

The transmission of action potentials along the axon without change in amplitude.

Signup and view all the flashcards

Refractory Period

Time after an action potential during which another cannot occur, preventing backpropagation.

Signup and view all the flashcards

Unmyelinated Axon Conduction

AP conduction occurs continuously along the axon membrane due to Na+ channel activation.

Signup and view all the flashcards

Spike Initiating Zone

The axon hillock where the threshold depolarization is reached to initiate an action potential.

Signup and view all the flashcards

Axon Diameter Effect

Larger axon diameter results in faster conduction speeds of action potentials.

Signup and view all the flashcards

Ions Flow

Ions transmit electrical signals between neurons.

Signup and view all the flashcards

Sychronous Activity

Simultaneous firing of neurons leading to escape responses.

Signup and view all the flashcards

Neurotransmitter Release

Exocytosis of neurotransmitters from vesicles into synaptic cleft.

Signup and view all the flashcards

Ca2+ Influx

Calcium ions entering neuron trigger neurotransmitter release.

Signup and view all the flashcards

Postsynaptic Binding

Neurotransmitter attaches to receptors causing depolarization or hyperpolarization.

Signup and view all the flashcards

First Messengers

Neurotransmitters that bind to ion channels directly.

Signup and view all the flashcards

G-Protein Coupled Receptors

Receptors that trigger secondary messenger pathways, affecting slow responses.

Signup and view all the flashcards

Exocytosis

Process where neurotransmitters are released from axon terminals when Ca2+ enters the cytoplasm.

Signup and view all the flashcards

Role of Ca2+ in exocytosis

Ca2+ ions trigger neurotransmitter release at the axon terminal during action potentials.

Signup and view all the flashcards

Neurotransmitter removal

Neurotransmitters are cleared from synaptic cleft by breakdown or reuptake.

Signup and view all the flashcards

Acetylcholine

A neurotransmitter that can stimulate or inhibit muscle contraction depending on receptor type.

Signup and view all the flashcards

Ionotropic receptors

Receptors that are ligand-gated ion channels, leading to immediate post-synaptic response.

Signup and view all the flashcards

Nicotinic receptor

A type of ionotropic receptor that acts as a Na+ channel, causing depolarization.

Signup and view all the flashcards

Metabotropic receptors

Receptors that influence post-synaptic responses indirectly through intracellular signals.

Signup and view all the flashcards

Muscarinic receptor

A metabotropic receptor that modulates responses of cardiac muscles, inhibiting contraction.

Signup and view all the flashcards

Depolarization

The process where the membrane potential becomes more positive due to Na+ influx.

Signup and view all the flashcards

Voltage-gated sodium channel (Na+v)

A channel that opens in response to a membrane depolarization, allowing Na+ to enter.

Signup and view all the flashcards

Peak depolarization

The point during an action potential where the membrane potential is at its highest.

Signup and view all the flashcards

Repolarization

The return of the membrane potential back towards resting potential after depolarization.

Signup and view all the flashcards

Study Notes

Depolarization - Rising Phase of Action Potential (AP)

  • Action potentials (APs) rely on ion currents and voltage-gated channels.
  • Sodium (Na+) channels are voltage-gated.
  • Potassium (K+) channels are voltage-gated.
  • Leak channels for Potassium (K+) are always open.
  • At time zero (t=0), voltage-gated Na+ and K+ channels are closed.
  • Stimulus opens these channels.
  • Na+ channels open, causing Na+ ions to flow in.
  • The cell becomes more depolarised.
  • Na+ channels close and inactivate, the peak of depolarization.

Falling Phase of AP

  • Depolarization depends on ion currents and voltage-gated channels.
  • Potassium (K+) channels open, causing K+ ions to flow out.
  • The cell repolarizes.
  • K+ channels remain open briefly beyond the resting membrane potential, causing hyperpolarization.
  • The Na+/K+ pump returns the cell to its resting membrane potential.

Hodgkin-Huxley Cycle

  • Action potential rise phase involves positive feedback.
  • Initial depolarization leads to further membrane depolarization, which increases Na+ flow.

Action Potential Propagation Along Axon

  • Action potentials start at the axon hillock.
  • They travel along the axon membrane without change.
  • Dendrites and cell bodies have K+ channels that prevent backward propagation.

Propagation of Action Potential

  • Action potentials move along an axon by the ion flow generated in one segment depolarizing the next.

AP Conduction in Unmyelinated Axons

  • Threshold is reduced at the axon hillock (spike-initiating zone).
  • Concentration of Na+ channels.
  • Current spreads along the membrane toward terminals(new action potential)

AP Conduction in Myelinated Axons

  • Myelin sheath insulation prevents ions from crossing the membrane, reducing current loss.
  • Ions are concentrated at nodes (nodes of Ranvier) allowing ions to cross the membrane.
  • Action potentials "jump" from node to node (saltatory conduction) increasing conduction velocity.
  • Axon diameter and myelin sheath affect the speed of conduction.

Synaptic Transmission

  • Chemical synapse is where a neuron communicates with another neuron or effector.
  • Pre-synaptic neuron releases neurotransmitters into the synaptic cleft.
  • Post-synaptic neuron receives the neurotransmitter and responds.

Two Types of Synapses

  • Electrical synapses: Direct ion flow between cells. rapid transmission; synchronicity; cannot be modulated, excitatory only.
  • Chemical synapses: Neurotransmitter release across a synaptic cleft; slower transmission; can be modulated.

Chemical Synapse

  • Pre- and Postsynaptic neurons separated by a synaptic cleft.
  • Neurotransmitters stored in vesicles within the axon terminals of the presynaptic neuron.
  • Action potential triggers calcium (Ca2+) influx into the axon terminal.
  • Neurotransmitter release (exocytosis) into the synaptic cleft.
  • Neurotransmitter binds to receptors on the postsynaptic membrane.
  • Ion channels open or close, causing postsynaptic response (depolarization or hyperpolarization).

Vesicles Release Neurotransmitter

  • Action potentials cause Ca2+ influx through voltage-gated Ca2+ channels.
  • Ca2+ causes vesicles to move to the plasma membrane, fuse, and release neurotransmitter into the cleft.

Postsynaptic Binding

  • Neurotransmitters bind to postsynaptic receptors.
  • Post-synaptic receptors will either be excitatory (depolarization) or inhibitory (hyperpolarization).
  • Allows integration of multiple presynaptic inputs.

Neurotransmitters Work in Two Ways

  • Some neurotransmitters bind to ligand-gated ion channels in the postsynaptic membrane.
  • Others work more slowly via acting as first messengers, binding to G-protein-coupled receptors, triggering a second messenger (leads to opening or closing of gated channels).

Review: Neurotransmitter Release

  • Neurotransmitters released from synaptic vesicles in the synaptic cleft by exocytosis.
  • Ca2+ ions trigger exocytosis- through voltage-gated Ca2+ channels opened by the arrival of the action potential.
  • Neurotransmitter release stops once action potentials cease.
  • Neurotransmitters removed from the synaptic cleft by enzymes or taken up by axon terminals or glial cells.

Neurotransmitters

  • Diverse kinds and diverse effects.
  • Bind to specific receptor proteins on the postsynaptic membrane, causing either stimulation or inhibition of an effector cell (depending on the receptor present).

e.g. Acetylcholine

  • Stimulates skeletal muscle, via nicotinic receptors.
  • Inhibits cardiac muscle, via muscarinic receptors.

Two Classes of Acetylcholine Receptor Proteins

  • Ionotropic receptors: Ligand-gated ion channels. The post-synaptic response is directly dependent on ion current (eg. nicotinic receptor is a Na+ channel).
  • Metabotropic receptors: Influencing postsynaptic cells indirectly through a second messenger system (eg. muscarinic receptor).

Experimental Research

  • Heart 1 connected to vagus nerve, shows a fast response.
  • Heart 2 does not receive signals from the vagus nerve, shows a slower response.
  • The solution from heart 1 caused the delayed, but similar response seen in heart 2

Studying That Suits You

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

Quiz Team

Related Documents

Lecture 7 Joan Forder PDF

Description

This quiz explores the intricacies of action potentials, focusing on the roles of sodium and potassium channels during various phases. It covers how these channels influence neuronal signaling and neurotransmitter release, along with the differences between electrical and chemical synapses. Test your understanding of these critical neurophysiological concepts!

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser