Neuroscience Action Potentials and Conduction

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Questions and Answers

What is the primary function of voltage-gated Na+ channels in cells?

To help propagate action potentials. (correct)

To facilitate myelination.

To increase membrane resistance.

To generate passive currents.

What is myelination and its role in signal conduction?

The wrapping of axons with Schwann cells and Oligodendrocytes to enhance conduction. (correct)

The formation of new neurons in the CNS.

The creation of synapses between neurons.

The process of increasing signal loss.

What is the effect of increasing the length constant ($\lambda$) on action potential propagation?

It decreases the conduction velocity.

It results in shorter distances for action potential propagation.

It increases the likelihood of signal loss.

It allows action potentials to travel further before diminishing. (correct)

How does myelination influence the membrane's electrical properties?

It increases membrane resistance and minimizes current leakage. Signup and view all the answers

Which cells are responsible for myelination in the peripheral nervous system (PNS)?

Schwann cells. Signup and view all the answers

What happens in biological tissue when a voltage is applied across the membrane?

There is a loss of voltage due to low conductance compared to copper. Signup and view all the answers

What is a key characteristic of cells that lack voltage-gated Na+ channels?

They can only conduct passive currents. Signup and view all the answers

How does myelination affect the number of layers around an axon?

Myelination can create approximately 50-100 layers of myelin around axons. Signup and view all the answers

What happens to an action potential (AP) when it encounters a poisoned node in an unmyelinated axon?

The AP skips the poisoned node and moves to the next healthy node. Signup and view all the answers

What is the primary reason why action potentials cannot propagate backward after entering the refractory period?

The voltage-gated Na+ channels are inactivated. Signup and view all the answers

How does myelination affect the conduction velocity of action potentials?

It increases conduction velocity substantially. Signup and view all the answers

What type of synapse allows for the rapid communication of electrical signals, such as those found in the heart?

Electrical synapse Signup and view all the answers

What is the effect of unmyelinated axons on action potential conductance velocity?

They result in a significantly slower conductance velocity. Signup and view all the answers

What is the role of the Nodes of Ranvier in myelinated axons?

They contain a dense concentration of Na+ and K+ voltage-gated channels. Signup and view all the answers

How do gap junctions contribute to the function of electrical synapses?

They allow for the direct passage of small ions and depolarization. Signup and view all the answers

What is the primary function of Schwann cells in the myelination process?

To encase multiple axons without forming a myelin sheath. Signup and view all the answers

What role do oligodendrocytes play in the myelination process?

They have processes that wrap multiple axons to enhance conduction. Signup and view all the answers

What is the primary effect of myelination on action potential propagation?

Allows for faster and more efficient transmission of impulses. Signup and view all the answers

What occurs at the Nodes of Ranvier during action potential propagation?

Action potentials regenerate due to voltage-gated sodium channels. Signup and view all the answers

How does increasing the diameter of an axon affect its internal resistance?

Decreases internal resistance, allowing less voltage loss. Signup and view all the answers

What phenomenon is described as action potentials 'jumping' from one node to the next?

Saltatory conduction Signup and view all the answers

What is the primary consequence of multiple sclerosis (MS) on neuro conduction?

Destruction of myelin sheath leading to signal blockage. Signup and view all the answers

What determines the ability of sodium ions to regenerate the action potential at the nodes?

Voltage-gated sodium channels at the nodes. Signup and view all the answers

Which of the following best explains why action potentials do not go backward?

Refractory periods prevent backward propagation of signals. Signup and view all the answers

Which characteristic of the membrane significantly affects current leakage during action potential propagation?

Membrane resistance influences current leakage. Signup and view all the answers

How are action potentials propagated in unmyelinated axons compared to myelinated axons?

Myelinated axons use saltatory conduction for faster transmission. Signup and view all the answers

Study Notes

Action Potentials and Axonal Conduction

Cells lacking voltage-gated sodium channels can conduct passive currents but cannot generate action potentials (APs).
Axons are essential for signal transmission over long distances.
Biological tissue is a poor conductor compared to copper wire, leading to voltage loss and signal degradation.
Myelination is the process of wrapping axons with myelin sheaths, significantly increasing conduction velocity.
Myelin sheaths are formed by glial cells: Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS).
Myelination increases membrane resistance, minimizing current leakage and enhancing conduction velocity.

Length Constant

The length constant (λ) measures the distance an AP can travel before its amplitude decays to 37% of its original value.
Increasing λ enhances the distance an AP can travel.
Increasing axon diameter reduces internal resistance (Ri), leading to less voltage loss and increased λ.
Increasing membrane resistance (Rm) prevents current leakage, further augmenting λ.

Myelination and Saltatory Conduction

Myelination significantly increases λ, typically by 20 times, due to its high membrane resistance and the reduction in current leakage.
Schwann cells wrap around portions of individual axons, while oligodendrocytes can wrap around multiple axons with their branching processes.
Nodes of Ranvier are gaps between myelin sheaths where APs are regenerated through voltage-gated sodium channels.
Myelination allows for saltatory conduction, where APs "jump" between nodes, minimizing energy expenditure and enhancing conduction velocity.

Unmyelinated Axons

Unmyelinated axons lack the multiple layers of myelin sheath, resulting in slower conduction velocities due to current leakage.
Unmyelinated axons have a lower membrane resistance and smaller diameter compared to myelinated axons.
Conduction velocity in myelinated axons is significantly higher (~80 m/s) compared to unmyelinated axons (~2 m/s).

Axon Terminal and Synaptic Transmission

The axon terminal is the endpoint of an axon, where APs trigger the release of neurotransmitters.
Electrical synapses allow rapid transmission of signals without the release of neurotransmitters via gap junctions formed by connexin proteins.
Chemical synapses rely on the release of neurotransmitters to transmit signals between neurons or effectors (muscles/glands).

Mechanisms Preventing AP Backflow

The refractory period of the membrane, due to the inactivation of voltage-gated sodium channels after an AP, prevents the backflow of an AP.
While there's still some passive movement of APs backward, the inactivated sodium channels inhibit the generation of a new AP in the preceding membrane area.

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Description

Explore the concepts of action potentials and axonal conduction in this quiz. Learn about the role of myelination and the length constant in enhancing signal transmission. Test your understanding of how biological tissues compare to conductors like copper wire.