Neurobiology: Nerve Action Potential Overview

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Questions and Answers

What happens to sodium ions when the inactivation gate of Na+ channels closes?

Sodium ions increase their permeability.

Sodium ions continue to enter the membrane.

Sodium ions can no longer enter the membrane. (correct)

Sodium ions are expelled from the membrane.

What triggers the closure of the inactivation gate in Na+ channels?

An increase in membrane voltage. (correct)

The influx of potassium ions.

The binding of neurotransmitters.

A decrease in membrane voltage.

During which phase cannot another action potential be elicited regardless of stimulus size?

Resting phase.

Depolarization phase.

Relative refractory period.

Absolute refractory period. (correct)

What role do K+ channels play during the action potential?

They increase potassium conductance after a delay. Signup and view all the answers

What is required to reopen the inactivation gate of Na+ channels?

A return to or approach of the resting membrane potential. Signup and view all the answers

What characterizes the relative refractory period?

A larger than usual inward current may elicit an action potential. Signup and view all the answers

What is the consequence of the closure of the inactivation gates in Na+ channels during action potential?

The membrane potential begins to repolarize. Signup and view all the answers

Why are K+ channels slightly delayed in opening during an action potential?

To ensure simultaneous repolarization with Na+ closing. Signup and view all the answers

What happens to tropomyosin when Ca2+ ions are absent in the sarcoplasm?

It returns to cover the myosin binding sites on actin Signup and view all the answers

What is the primary factor that represents active tension during muscle contraction?

The difference between total tension and passive tension Signup and view all the answers

During the relaxation of a muscle, what occurs to the thin filament?

It slides back to its original position Signup and view all the answers

Active tension during isometric contraction is most directly proportional to what?

The number of cross-bridges formed Signup and view all the answers

What role do Ca2+ ions play in muscle contraction?

They bind to troponin, allowing tropomyosin to move Signup and view all the answers

Which term refers to the tension developed by stretching a muscle without stimulation?

Passive tension Signup and view all the answers

What is total tension in the context of muscle contraction?

The combined effects of both active and passive tension Signup and view all the answers

What physiological state occurs when there are no Ca2+ ions present during muscle contraction?

The muscle returns to its original relaxed position Signup and view all the answers

What occurs in the presynaptic cell prior to neurotransmitter release?

Depolarization due to an action potential Signup and view all the answers

Which ion is primarily responsible for the depolarization phase of the action potential?

Na+ Signup and view all the answers

What effect do inhibitory neurotransmitters have on the postsynaptic membrane?

They hyperpolarize the membrane Signup and view all the answers

What is the primary intracellular cation at resting membrane potential?

K+ Signup and view all the answers

During the rapid opening of Na+ channels, what drives membrane potential equilibrium?

Sodium influx Signup and view all the answers

What is the correct sequence of events in action potential transmission?

Depolarization, sodium channel opening, repolarization Signup and view all the answers

Which of the following statements about neuromuscular transmission is true?

Neurotransmitters bind to the postsynaptic cell membrane Signup and view all the answers

Which concept is accurately described regarding potassium ions during action potential?

Potassium efflux occurs during the repolarization phase Signup and view all the answers

What primarily causes the membrane potential to become more negative during repolarization?

Outward flux of K+ ions Signup and view all the answers

Which factor contributes to increased conduction velocity in nerve fibers?

Myelination of axons Signup and view all the answers

During the action potential process, what is the condition under which depolarization occurs?

When conditions are right at any point on the membrane Signup and view all the answers

What is the smallest part of a muscle fiber capable of contraction?

Sarcomere Signup and view all the answers

What significant structural feature of skeletal muscle fibers allows them to function as a single unit?

Multinucleation Signup and view all the answers

Which of the following is NOT a result of increased K+ conductance during repolarization?

Cell interior becomes less negative Signup and view all the answers

What is the main structural characteristic of myofibrils?

Interdigitating thick and thin filaments Signup and view all the answers

What is one of the roles of T tubules in skeletal muscle fibers?

Facilitating contraction signaling Signup and view all the answers

What occurs during isometric contraction?

The muscle develops tension without changing length. Signup and view all the answers

What leads to rigor mortis after death?

Absence of ATP causing inability to detach actin and myosin. Signup and view all the answers

In isotonic contraction, which of the following statements is correct?

The force of contraction exceeds the load being moved. Signup and view all the answers

What is the primary role of ATP in muscle contraction?

To facilitate the separation of actin and myosin during relaxation. Signup and view all the answers

What characterizes an isometric contraction?

Muscle maintains a constant length while developing tension. Signup and view all the answers

What happens to calcium ions during muscle relaxation?

They are absorbed by the sarcoplasmic reticulum. Signup and view all the answers

Why does a muscle not shorten during an isometric contraction?

The force produced is equal to the load. Signup and view all the answers

What defines the relationship between force and velocity in muscle contractions?

Muscle velocity decreases as the load increases. Signup and view all the answers

Study Notes

Nerve Action Potential Overview

Action potential in the presynaptic cell triggers depolarization, leading to neurotransmitter release.
Calcium influx at the presynaptic terminal results in neurotransmitter discharge into the synaptic cleft.
Neurotransmitters bind to receptors on the postsynaptic membrane, influencing cellular responses.
Inhibitory neurotransmitters hyperpolarize the postsynaptic membrane, making it less likely to fire.

Ionic Distribution and Membrane Potential

Extracellular fluid primarily contains Na+, Cl-, and Ca2+; intracellular fluid is rich in K+ and negatively charged anions.
Membrane transport is guided by the principle of potassium in and sodium out (PiSo).

Action Potential Dynamics

Characterized by rapid depolarization due to the opening of Na+ channels, followed by repolarization.
Inactivation gates of Na+ channels close shortly after activation, preventing further Na+ entry and promoting repolarization.
Sodium channels remain closed until the membrane potential nears resting state, making reactivation difficult until repolarization occurs.

Refractory Periods

Absolute Refractory Period: No new action potential can be generated, regardless of stimulus strength; coincides with the entire action potential duration.
Relative Refractory Period: Occurs post-absolute period; a stronger-than-usual stimulus can induce an action potential.

Muscle Contraction Types

Isometric Contraction: Muscle length remains unchanged while tension develops; observed when the load exceeds muscle force.
Isotonic Contraction: Muscle changes length while tension remains constant; force exceeds load, resulting in movement.

Cross-Bridge and Rigor Mortis

Rigor mortis occurs post-mortem due to the depletion of ATP, preventing muscle relaxation and leading to sustained contraction.

Calcium Dynamics and Muscle Relaxation

Ca2+ is reabsorbed by the sarcoplasmic reticulum via ATP-dependent pumps after contraction.
Absence of Ca2+ leads to myosin binding sites on actin being covered by tropomyosin, halting contraction.

Length-Tension Relationship

Describes tension during isometric contraction:
- Passive Tension: Generated through muscle stretching.
- Total Tension: Resulting from muscle stimulation.
- Active Tension: Difference between total and passive tensions, indicating force produced from cross-bridge cycling.

Propagation of Action Potential

Action potentials spread in multiple directions across the excitable membrane.
The all-or-nothing principle dictates that depolarization occurs only under appropriate conditions.

Factors Affecting Conduction Velocity

Fiber Size: Larger diameter reduces internal resistance, increasing conduction speed.
Myelination: Myelin insulates axons, enhancing conductivity and propagation of action potentials.

Skeletal Muscle Structure

Muscle fibers are multinucleated and consist of myofibrils encased by the sarcoplasmic reticulum and T tubules.
Sarcomeres, composed of thick and thin filaments, are the contractile units marked by Z lines, contributing to striated muscle appearance.

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Description

This quiz explores the mechanisms behind nerve action potentials, focusing on the role of depolarization, neurotransmitter release, and ionic distribution. It covers critical dynamics of action potentials and the effects of neurotransmitters on postsynaptic cells. Test your understanding of these fundamental concepts in neurobiology.