Neuroscience Action Potentials and Conduction

Questions and Answers

What triggers the opening of voltage-gated sodium channels during an action potential?

Membrane depolarization to threshold (correct)

Decrease in sodium concentration

Increase in potassium permeability

Membrane hyperpolarization

During the falling phase of the action potential, which ion primarily rushes out of the cell?

Sodium (Na)

Calcium (Ca)

Potassium (K) (correct)

Chloride (Cl)

What happens to the membrane potential during the overshoot phase?

It returns to the resting membrane potential

It goes close to the equilibrium potential for sodium (E Na) (correct)

It decreases the driving force on sodium

It becomes negative relative to resting potential

What occurs immediately after the voltage-gated sodium channels inactivate?

Voltage-gated potassium channels open Signup and view all the answers

What is the primary cause of hyperpolarization during the undershoot phase?

Increased potassium conductance Signup and view all the answers

What is the effect of high potassium permeability during the action potential?

It causes brief hyperpolarization Signup and view all the answers

What defines the threshold in the context of an action potential?

The membrane potential at which sufficient sodium channels open Signup and view all the answers

Which phase of the action potential is characterized by a rapid influx of sodium ions?

Rising phase Signup and view all the answers

What is the primary function of oligodendroglial and Schwann cells?

Providing insulation for axons Signup and view all the answers

Where are oligodendroglial cells primarily found?

In the central nervous system Signup and view all the answers

What is the process called when current flows by jumping from one node to the next?

Saltatory conduction Signup and view all the answers

Which type of cell myelinates only a single axon?

Schwann cells Signup and view all the answers

What type of channels are concentrated at the nodes of Ranvier?

Voltage-gated sodium channels Signup and view all the answers

Why do the membranes of dendrites and neuronal cell bodies not generate sodium-dependent action potentials?

They have very few voltage-gated sodium channels. Signup and view all the answers

Which statement regarding myelinated nerve fibers is correct?

They exhibit saltatory conduction at the nodes. Signup and view all the answers

What is the significance of the nodes of Ranvier in myelinated fibers?

They are sites of increased membrane permeability. Signup and view all the answers

What concept was significantly supported by Otto Loewi's research?

Chemical synapses Signup and view all the answers

What type of synapse allows for the direct transfer of ionic current between cells?

Electrical synapse Signup and view all the answers

Which of the following statements about electrical synapses is true?

They have specialized sites called gap junctions. Signup and view all the answers

What did Bernard Katz and his colleagues demonstrate regarding synaptic transmission?

Fast transmission at the synapse is chemically mediated. Signup and view all the answers

What was the outcome when the vagus nerve was electrically stimulated in Loewi's experiment?

It released a chemical affecting the heartbeat. Signup and view all the answers

Who conclusively demonstrated the existence of chemical synapses in the context of motor neuron axons and skeletal muscle?

Bernard Katz Signup and view all the answers

Which statement best describes the speed of transmission at electrical synapses?

They are faster than chemical synapses. Signup and view all the answers

What role do chemical synapses play in the nervous system?

They are crucial for all operations of the nervous system. Signup and view all the answers

What happens to the magnitude of a potential change when the current pulse is below the threshold for generating an action potential?

It decays with increasing distance from the site of injection. Signup and view all the answers

How does passive conduction compare to active conduction in terms of the amplitude of potential responses along an axon?

Active conduction maintains a constant amplitude while passive conduction decreases. Signup and view all the answers

What is the effect of using a depolarizing current pulse that produces an action potential?

The electrical signaling propagates without any decrement. Signup and view all the answers

What is a consequence of current leaking out of the axon during passive conduction?

Decreased amplitude of potential changes Signup and view all the answers

What does the term 'active conduction' refer to in this context?

Conduction that involves repetitive generation of action potentials Signup and view all the answers

If an electrode generates a supra-threshold current, what kind of response is evoked?

An action potential Signup and view all the answers

What does the recorded action potential demonstrate in relation to its amplitude?

Amplitude is constant along the length of the axon. Signup and view all the answers

As distance increases from the site of action potential generation, what happens to the time of appearance of the action potential?

It becomes delayed. Signup and view all the answers

What structure is formed when six connexin subunits combine?

Connexon Signup and view all the answers

What type of synapse allows ionic current to pass equally well in both directions?

Electrical synapse Signup and view all the answers

What happens to the membrane potential when Na+ ions enter the postsynaptic cell through transmitter-gated ion channels?

Depolarization occurs Signup and view all the answers

Where are gap junctions typically found in relation to neuron activity?

In neurons requiring highly synchronized activity Signup and view all the answers

What induces an electrical post-synaptic potential (PSP) in a second neuron?

Action potential in a first neuron Signup and view all the answers

In the generation of an excitatory post-synaptic potential (EPSP), what primarily triggers the release of neurotransmitters?

An action potential in the presynaptic terminal Signup and view all the answers

What is the gap between two cells at a gap junction typically measured to be?

3 nm Signup and view all the answers

What type of potential is generated when neurotransmitters bind to receptor sites on the postsynaptic membrane?

Excitatory post-synaptic potential (EPSP) Signup and view all the answers

Study Notes

Action Potential

Action potentials maintain constant amplitude regardless of distance.
Threshold is the membrane potential required for sodium channels to open significantly.
Rising phase involves sodium channels opening, allowing Na+ influx, leading to rapid depolarization.
Overshoot occurs as membrane potential nears E_Na, exceeding 0 mV due to high sodium permeability.
Falling phase marks the inactivation of sodium channels and opening of potassium channels, driving K+ out and repolarizing the membrane.
Undershoot happens when K+ channels remain open, hyperpolarizing the membrane below resting potential until closure.

Saltatory Conduction

Myelinated fibers possess an insulating myelin sheath, with gaps known as nodes of Ranvier.
Oligodendroglial cells myelinate multiple axons in the CNS, while Schwann cells myelinate a single axon in the PNS.
Current jumps between nodes in saltatory conduction, facilitated by concentrated voltage-gated sodium channels at the nodes.

Electrical Conduction

Passive conduction results in potential decay over distance when currents are subthreshold, limiting effect to short distances.
Active conduction occurs when an action potential is generated; the amplitude remains constant along the axon despite delays in propagation.

Synaptic Transmission

Understanding synaptic transmission is essential for comprehending neural functions, drug effects, and mental disorders.
Otto Loewi's experiments in 1921 highlighted chemical synapse functionality through neurotransmitter release in response to electrical stimulation.
Bernard Katz confirmed fast synaptic transmission through chemical means at neuromuscular junctions.

Electrical Synapses

Electrical synapses, identified in the late 1950s, use gap junctions for direct ionic current transfer between cells.
Gap junctions consist of connexin proteins forming connexons that facilitate rapid, bidirectional communication.
Electrical coupling via gap junctions is vital for synchronized neuronal activity.

Chemical Synapses

Excitatory Post Synaptic Potential (EPSP) occurs when neurotransmitter release leads to Na+ influx in the postsynaptic cell, causing depolarization.
Inhibitory Post Synaptic Potential (IPSP) involves neurotransmitter-induced hyperpolarization of the postsynaptic membrane, reducing neuronal excitability.

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Description

This quiz covers the mechanisms of action potentials, including the phases of depolarization and repolarization. Additionally, it explores saltatory conduction in myelinated fibers and the role of oligodendrocytes and Schwann cells. Test your understanding of these essential neuroscience concepts.