Nerve Impulse Conduction Theories

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Questions and Answers

How does an increase in the number of open ion channels affect membrane resistance?

It has no effect on membrane resistance.

It decreases membrane resistance. (correct)

It leads to total resistance across the membrane.

It increases membrane resistance.

What happens to the local current when membrane resistance is low?

The local current dissipates more across the membrane. (correct)

The local current spreads less effectively.

The local current increases in strength.

The local current becomes more concentrated.

What is the relationship between local current effect and ion channels?

Ion channels have no effect on local current spread.

Fewer open ion channels enhance the local current effect.

More open ion channels limit the spread of local current.

More open ion channels facilitate the spread of local current. (correct)

Which statement best reflects the impact of membrane resistance on local current?

Lower resistance results in greater local current loss. Signup and view all the answers

How does opening more ion channels affect the spread of local current?

It limits the spread of local current. Signup and view all the answers

What is multiple sclerosis primarily classified as?

An autoimmune disease Signup and view all the answers

What does multiple sclerosis primarily damage in the central nervous system (CNS)?

Myelin Signup and view all the answers

Which part of the nervous system is affected by multiple sclerosis?

Central nervous system Signup and view all the answers

In multiple sclerosis, what role does the immune system play?

It attacks the myelin Signup and view all the answers

Which statement accurately reflects the nature of multiple sclerosis?

It leads to the degeneration of myelin in the CNS. Signup and view all the answers

Which property of the axon contributes to a high conduction velocity by reducing cytoplasmic resistance?

Large axon diameter Signup and view all the answers

How does low membrane capacitance affect an axon's conduction velocity?

It decreases the time required to change membrane potential Signup and view all the answers

Which combination of properties is most beneficial for achieving high conduction velocity in axons?

Low resistance and low capacitance Signup and view all the answers

What is the formula for calculating conduction velocity?

conduction velocity = distance / time Signup and view all the answers

What does high membrane resistance contribute to in terms of axonal conduction?

Enhanced signal propagation Signup and view all the answers

Which of the following is NOT a factor that contributes to high conduction velocity in axons?

High membrane capacitance Signup and view all the answers

What initiates an action potential in an axon?

Stimulation of a group of axons to threshold Signup and view all the answers

Which factor is essential in determining the conduction velocity?

The distance between the electrodes Signup and view all the answers

What does the time gap between stimulus and action potential indicate?

The conduction velocity Signup and view all the answers

Which of the following describes how conduction velocity is measured?

By measuring distance and time Signup and view all the answers

What is one possible consequence of improperly myelinated axons?

Complete block of action potentials Signup and view all the answers

How does decreased conduction velocity affect nerve signal transmission?

Some action potentials may be transmitted, while others are not Signup and view all the answers

Which of the following best describes the effect of inadequate myelination on axons?

It may lead to a block in action potential transmission Signup and view all the answers

What might result from the inability of myelinated axons to conduct action potentials properly?

Decreased efficiency in signal transmission Signup and view all the answers

What is a potential outcome when only some action potentials are transmitted?

Variable response to stimuli Signup and view all the answers

What effect does a high capacitance in the lipid bilayer have on current charging?

It requires more current to charge. Signup and view all the answers

How does high capacitance influence the spread of local current?

It can decrease the spread of local current with brief current pulses. Signup and view all the answers

What is a consequence of high capacitance in response to brief current pulses?

It can cause a delay in the current response. Signup and view all the answers

In the context of the lipid bilayer, what happens when capacitance is increased?

More current is needed for a similar charge effect. Signup and view all the answers

Which statement accurately describes the relationship between current pulses and high capacitance?

High capacitance can lead to decreased local current spread during brief pulses. Signup and view all the answers

Study Notes

Electrical Excitability of Nerve Impulse Conduction

The lecture aims to explain how the resting nerve fiber membrane potential is raised to threshold, describe extracellular recordings, demonstrate local circuit theories of nerve impulse propagation, apply the effect of nerve fiber diameter and myelin on nerve conduction, and distinguish clinical applications like demyelination.

Electrical Stimulation

Electrical stimulation occurs under a cathode (negative charge), reducing excitability.
Conversely, it decreases under an anode (positive charge).
This process can initiate an action potential in an axon or group of axons by reaching threshold.

Extracellular Recording

Extracellular recordings of action potentials provide information about conduction velocity under various conditions.
Diphasic recording shows a biphasic waveform.
Monophasic recording displays a single waveform shape, revealing differences between intact and damaged axons.

Conduction Velocity

Conduction velocity is calculated by dividing the distance between stimulating and recording electrodes by the time gap between stimulus and action potential recording.
Velocity = Distance/Time

Action Potential Conduction

Changes in membrane potential in one axon part spread to adjacent areas due to local currents.
Conduction velocity depends on how far local currents spread along the axon.
Depolarization of an axon section to threshold initiates an action potential at that location.

Length Constant

The length constant (λ) measures the distance a potential change travels to reach 37% of its original value.

Factors Affecting Conduction Velocity

High membrane resistance and low membrane capacitance enhance conduction velocity by enabling local currents to propagate further.
High axonal diameter decreases cytoplasmic resistance, improving conduction velocity.

Capacitance

Capacitance (C) is the ability of the lipid bilayer to store charge.
High capacitance results in needing more current for charging or longer charging time, affecting local current spread, especially with short current pulses.

Membrane Resistance

Membrane resistance is influenced by the number of open ion channels.
Lower resistance correlates with more open ion channels and more local current loss across the membrane, reducing current spread.

Action Potential Propagation

Local currents propagate the action potential down the axon.
An axon area that has just fired an action potential is refractory, so it cannot fire another until recovery.

Refractory Period

The refractory period prevents backward propagation of action potentials.

Myelin Sheath

Myelin significantly increases conduction velocity in axons.
Larger-diameter axons (e.g., motoneurons) are myelinated, while smaller axons (e.g., sensory fibers) are often not.
Myelin reduces capacitance and increases axon resistance.

Schwann Cells and Oligodendrocytes

Schwann cells myelinate peripheral axons, while oligodendrocytes myelinate axons in the central nervous system.

Fiber Diameter and Velocity Relationship

Conduction velocity is proportional to fiber diameter in myelinated axons.
The highest velocity in mammals is achieved by large-diameter myelinated axons.
In unmyelinated axons, conduction velocity correlates with the square root of fiber diameter.

Demyelination

Demyelination is a condition where sections of axons lose their myelin sheath.
Multiple sclerosis is a prominent demyelinating disease.
Damage to myelin can dramatically reduce the ability of axons to conduct action potentials, influencing and sometimes blocking conduction velocity.

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Description

This quiz covers the mechanisms of nerve impulse conduction, including factors affecting resting membrane potential and the role of electrical stimulation. Participants will explore concepts such as extracellular recordings and the impact of nerve fiber characteristics on conduction velocity. The quiz also highlights clinical aspects like demyelination effects.