Neuroscience Action Potentials Quiz

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Questions and Answers

What is the primary effect of subthreshold stimulation on an axon?

A refractory period is initiated

An inhibitory potential is produced

An excitatory potential is produced but does not elicit an action potential (correct)

An action potential is generated

What characterizes conduction in a myelinated axon?

Conduction is slow due to numerous Na+ channels

Na+ channels are distributed throughout the entire axon

Conduction occurs continuously along the axon

Na+ channels are present only at the nodes of Ranvier (correct)

What causes action potentials to travel in one direction along an axon?

Inactivation of Na+ channels in the refractory period (correct)

Increased number of Na+ channels along the axon

The presence of K+ channels blocking Na+ entry

Myelination of the axon prevents signal loss

Which feature of unmyelinated axons contributes to slower conduction speeds?

Na+ channels are distributed throughout, causing delays in potential spread Signup and view all the answers

Why do action potentials travel faster down myelinated axons compared to unmyelinated axons?

Myelination creates insulation reducing signal leakage Signup and view all the answers

What initiates the action potential in neurons?

Activation of voltage-activated Na+ channels Signup and view all the answers

During which phase do Na+ channels become inactive, preventing further depolarization?

Absolute refractory period Signup and view all the answers

What causes K+ ions to flow out of the cell during the action potential?

The positive charge inside the cell Signup and view all the answers

What happens during the hyperpolarization phase?

Membrane potential becomes more negative than resting potential Signup and view all the answers

What is essential for another action potential to occur after an initial one?

Returning to resting membrane potential Signup and view all the answers

What primarily causes the rapid depolarization during an action potential?

Na+ ions rapidly flowing into the cell Signup and view all the answers

Which statement best describes the function of the Na+/K+ pump during an action potential?

It has no effect during the action potential Signup and view all the answers

What is the role of the inactivation mechanism of Na+ channels?

To stop Na+ flow and prevent continuous depolarization Signup and view all the answers

What is a characteristic of the hormone secretion process?

Hormones are often secreted in a pulsatile and rhythmic manner. Signup and view all the answers

Which hormone type is primarily able to cross the plasma membrane?

Steroid hormones Signup and view all the answers

What determines the multiplicity of action in hormone function?

The variety of targets, tissue type, and receptor type Signup and view all the answers

Which of the following statements about hormone receptors is true?

Receptors can either be membrane-bound or located inside the cell. Signup and view all the answers

How do hormone interactions influence physiological effects?

Two hormones released simultaneously can produce different effects than when released individually. Signup and view all the answers

What role do neuroendocrine cells play in hormone function?

They function as a bridge between the nervous system and the endocrine system. Signup and view all the answers

What is the purpose of radioimmunoassay in hormone measurement?

To measure hormone levels in blood and determine prevalence. Signup and view all the answers

Which type of hormone typically leads to faster physiological responses?

Peptide hormones Signup and view all the answers

What is the primary role of serotonin in the nervous system?

It organizes cortical networks and helps us perceive sensory patterns. Signup and view all the answers

How do hallucinogens primarily affect consciousness?

They create radical changes to perception and thought. Signup and view all the answers

What characterizes the retrograde transmission of endocannabinoids?

It allows endocannabinoids to weaken synaptic connections. Signup and view all the answers

What is a known effect of nicotine on the nervous system?

It activates acetylcholine receptors and acts as a mild psychostimulant. Signup and view all the answers

What happens to adenosine levels throughout the day?

Adenosine builds up across the day to induce sleepiness. Signup and view all the answers

What potential impact does heavy cannabis use have on memory?

It can cause trouble with memory due to THC acting as a cannabinoid receptor agonist. Signup and view all the answers

Which of the following best describes the function of acetylcholine in the body?

It causes muscle contraction through its receptors in muscle tissues. Signup and view all the answers

What unique feature do endocannabinoids possess regarding their synthesis and release?

They are synthesized in response to demand rather than stored. Signup and view all the answers

What is the primary role of dopamine D2 receptor antagonists in the treatment of schizophrenia?

To block excessive dopamine activity Signup and view all the answers

According to the dopamine theory of schizophrenia, what is observed in individuals with schizophrenia?

They experience a reduction in positive symptoms with D2R antagonists. Signup and view all the answers

What do psychostimulants primarily affect in the brain?

The dopamine, norepinephrine, and serotonin systems Signup and view all the answers

In the Salamone T maze task, what was observed when dopamine antagonists were introduced?

Rats switched to the easier low reward option. Signup and view all the answers

What effect does positive reward prediction error have on dopamine levels according to Schultz et al.?

It results in increased firing of dopamine neurons. Signup and view all the answers

What occurs when a predicted reward is not delivered, based on reward prediction error?

Dopamine levels decrease. Signup and view all the answers

How do psychostimulants differentiate between euphoria and symptoms similar to schizophrenia?

High doses can lead to temporary psychosis. Signup and view all the answers

Which of the following best represents the loss of motivation in the context of dopamine manipulation?

It leads to switching to easier tasks despite unfulfilled expectations. Signup and view all the answers

Study Notes

Action Potentials

Action potentials (APs) are generated and conducted by voltage-activated ion channels, primarily sodium channels (Na+).
At rest, Na+ channels are closed, but when the membrane potential reaches the threshold of -55mV, they open due to a conformational change.
Small depolarizations do not trigger APs because Na+ channels remain closed, but they are voltage-gated and open when the membrane potential reaches the threshold.
The electrochemical gradient drives Na+ ions into the cell, causing depolarization.
During rapid depolarization, Na+ channels open, allowing Na+ influx and flipping the membrane potential from negative to positive.
Na+ channels have an inactivation mechanism that automatically shuts them off after approximately 1 millisecond.
Inactivated Na+ channels cannot open again until the membrane potential returns to the resting state, creating an absolute refractory period.
Repolarization is driven by potassium (K+) ions moving out of the cell.
K+ leak channels are always open, but during AP, voltage-gated K+ channels open, allowing more K+ out of the cell.
The slow closing of these voltage-gated K+ channels leads to a hyperpolarization phase and a relative refractory period.
The Na+/K+ pump restores ion balance over time but does not contribute directly to AP generation.
Subthreshold stimulation produces an excitatory potential that is not strong enough to elicit an AP.
Supra-threshold stimulation produces an excitatory potential that exceeds the threshold, generating an AP that propagates down the axon.
Conduction in unmyelinated axons is slow because Na+ channels are present along the entire axon, requiring more Na+ influx for signal propagation.
Myelin insulates axons, reducing ion leakage and speeding up conduction.
In myelinated axons, Na+ channels are concentrated at the nodes of Ranvier, the gaps between myelin sheaths.
Myelinated axons conduct APs faster because fewer Na+ channels are required for signal propagation.
APs travel in one direction because Na+ channels in the wake of the AP are inactivated, preventing retrograde propagation.

Dopamine and Schizophrenia

Schizophrenia medications are dopamine D2 receptor antagonists, blocking D2 receptors to counteract the effects of excessive dopamine in the brain.
The dopamine theory of schizophrenia suggests that high levels of dopamine are associated with the disorder's positive symptoms.
Individuals with schizophrenia do not exhibit higher baseline levels of pleasure, but their positive symptoms (delusions, hallucinations, disorganized thoughts and speech) are reduced by D2 receptor antagonists.

Psychostimulants and Dopamine

Psychostimulants act as agonists on the monoamine systems, particularly dopamine, norepinephrine, and serotonin.
These drugs induce various effects, including euphoria, but high doses can cause temporary psychosis.
The effects of psychostimulants on dopamine are similar to those observed with schizophrenia.

Separating Pleasure from Motivation

Studies using the T-maze task have shown that dopamine antagonists reduce motivation but not pleasure.
In the task, rats were presented with options involving different levels of effort and reward.
Dopamine antagonists caused rats to shift their preference towards lower effort, higher reward options despite not affecting their ability to enjoy rewards.

Dopamine and Reward Prediction Error

Dopamine neurons in the ventral tegmental area (VTA) exhibit specific firing patterns related to reward prediction.
At first, they fire in response to unexpected rewards, but after learning, they fire in anticipation of expected rewards.
When a predicted reward is not delivered, dopamine neuron firing decreases.
Dopamine appears to play a role in encoding reward prediction error, the difference between expected and actual rewards.

Hallucinogens

Psychedelic drugs act as serotonin receptor agonists, altering conscious perception and thoughts with minimal impact on mood.
Recent research is exploring the therapeutic potential of hallucinogens for conditions like end-of-life care, PTSD, addiction, and more.
Serotonin plays a crucial role in organizing cortical networks, contributing to our perception of sensory patterns.

Acetylcholine

Acetylcholine was the first discovered neurotransmitter, found at the neuromuscular junction.
Motor neurons release acetylcholine into muscle tissue, causing muscle contractions in both skeletal and smooth muscles.
Acetylcholine is also present in the basal forebrain, implicated in functions like wakefulness and attention.
Nicotine is an acetylcholine receptor agonist, activating acetylcholine receptors and causing various effects, including mild psychostimulant effects.

Endocannabinoids

Endocannabinoids are neurotransmitters that bind to cannabinoid receptors, both of which are G protein-coupled receptors (GPCRs).
Unlike conventional neurotransmitters, endocannabinoids are produced on demand in dendrites and not stored in vesicles.
Endocannabinoids can travel from dendrites to axons, demonstrating retrograde transmission.
They have an inhibitory effect, weakening the connection between two cells at the synapse by reducing neurotransmitter release.
THC in cannabis is a cannabinoid receptor agonist, potentially explaining the memory impairments associated with heavy cannabis use.

Adenosine

Adenosine is a byproduct of ATP metabolism.
Adenosine receptors build up throughout the day, increasing inhibition and contributing to sleepiness.

The Hypothalamus and Neuroendocrine Cells

The hypothalamus (HTh) is the link between the nervous system and the endocrine system.
It contains neuroendocrine cells (neurosecretory cells) that release hormones into the bloodstream rather than onto neurons.
Some hormones have dual functions as neurotransmitters, such as epinephrine and norepinephrine.

Hormone Types

Peptide hormones are large chains of amino acids and typically act outside of the cell.
Amine hormones are small, single-segment molecules, with some acting inside the cell.
Steroid hormones are unique in their ability to cross cell membranes, allowing them to act inside the cell.

Hormone Receptor Types

Membrane receptors, such as GPCRs, are located on the cell surface and generally mediate fast hormonal effects.
Intracellular receptors, located near the nucleus, primarily function as transcription factors and typically mediate slow hormonal effects.
Steroid hormones can act through both membrane and intracellular receptors.

Methods for Measuring Hormones and Receptors

Radioimmunoassay measures hormone levels in blood, providing information about hormone prevalence.
Autoradiography identifies brain areas affected by hormones by using radioactive hormones to label their binding sites.

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Description

Test your understanding of action potentials and how voltage-activated ion channels, particularly sodium channels, function in generating and conducting electric signals in neurons. This quiz covers the mechanisms of depolarization, inactivation, and repolarization associated with action potentials.