Neuroscience: Neuron Function and Action Potentials

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Questions and Answers

What effect can activating a single neuron have on decision making?

It can bias decision making. (correct)

It has no effect on decision making.

It improves decision-making accuracy.

It causes immediate electrical paralysis.

What is the role of dendrites in a neuron?

To receive input from other neurons (correct)

To transmit action potentials

To process inputs

To generate new neurons

How are action potentials generated in neurons?

When input exceeds an intrinsic threshold. (correct)

Through continuous stimulation from surrounding neurons.

By constant ion flow through the axon.

Through the accumulation of neurotransmitters.

What characterizes an action potential?

It is either triggered or not triggered, known as an 'all or none' event. Signup and view all the answers

What factor primarily carries information in an action potential?

The timing or frequency of the action potentials. Signup and view all the answers

What initiates the changes in membrane potential that lead to an action potential?

The flow of positively-charged ions across the cell membrane. Signup and view all the answers

When was the action potential first discovered?

In 1865 Signup and view all the answers

Why was the mechanism of action potentials not fully understood for over 100 years?

Imperfect technology limited explorations. Signup and view all the answers

What is the typical resting membrane potential of a cell?

-70 mV Signup and view all the answers

What triggers the configurational change in ion channel structure?

Chemical messengers Signup and view all the answers

According to Bernstein's hypothesis, what primarily causes an action potential?

A non-specific increase in membrane permeability Signup and view all the answers

What happens to ion movement when ions can move freely across the cell membrane?

They will diffuse until concentration is equal on both sides Signup and view all the answers

How does the semi-permeable cell membrane affect ion movement?

It controls movement by allowing some ions to pass and not others Signup and view all the answers

What was a significant problem with Bernstein's hypothesis as shown by subsequent experiments?

Membrane potential was shown to exceed 0 mV Signup and view all the answers

What role do ion channels play in cellular processes?

They allow specific ions to cross the membrane Signup and view all the answers

Which ions are mentioned as being relevant to the membrane potential in the content?

Potassium (K+) Signup and view all the answers

What does the capacitance in the integrate-and-fire model represent?

The ability of the cell membrane to store charge Signup and view all the answers

What is represented by the equation dV(t)/dt = I(t) / C?

The relationship between voltage, current, and capacitance Signup and view all the answers

What does 'I(t)' symbolize in the context of the integrate-and-fire model?

The current injected into the neuron Signup and view all the answers

In the integrate-and-fire model, what does the slope of the voltage over time indicate?

The rate of change of the membrane potential Signup and view all the answers

Why does the integrate-and-fire model ignore the action potential generating mechanism?

It is designed to simplify the neuron’s electrical activity Signup and view all the answers

What does the term 'phenomenological model' imply in the context of the integrate-and-fire model?

A model focused on observable phenomena rather than underlying mechanisms Signup and view all the answers

What effect does injecting a square wave of current have on the neuron?

It influences the voltage over time Signup and view all the answers

What is the primary calculation that can be performed using the differential equation derived from the integrate-and-fire model?

To calculate voltage based on the slope at each time Signup and view all the answers

What happens to the voltage when a positive current is injected into the neuron according to the integrate-and-fire model?

The voltage will increase over time Signup and view all the answers

Which factor is central to the behavior described by the integrate-and-fire model?

Voltage changes over time Signup and view all the answers

What does the voltage function V(t) illustrate in the integrate-and-fire model?

The voltage at any time t based on current injected Signup and view all the answers

The term 'current' in the context of the cell membrane refers to what?

The flow of charge across the membrane Signup and view all the answers

In the context of the integrate-and-fire model, what does 'V(t+dt)' represent?

The voltage after a time increment dt following current injection Signup and view all the answers

How does the integrate-and-fire model simplify the study of neuron activity?

By eliminating complexities related to ion channels Signup and view all the answers

What is the purpose of injecting a square wave of current into the neuron?

To create an action potential Signup and view all the answers

Which equation represents the balance of current in the integrate-and-fire model?

$dV(t)/dt = C I(t)$ Signup and view all the answers

In the context of the integrate-and-fire model, what does 'C' represent?

Capacitance of the neuron Signup and view all the answers

What is typically represented by 'Vrest' in neural models?

The resting membrane potential Signup and view all the answers

What does the 'I(t)' variable signify in the model?

Injected current Signup and view all the answers

What is the main outcome of using the integrate-and-fire model?

Understanding the dynamics of action potentials Signup and view all the answers

What aspect does the integrate-and-fire model primarily focus on?

Voltage integration in neurons Signup and view all the answers

Which of the following best describes the action potential in a neuron?

A rapid increase and decrease in voltage Signup and view all the answers

What happens to the neuron's voltage when a square wave current is applied?

It fluctuates between threshold potentials Signup and view all the answers

What is the role of the integrate-and-fire model in neuroscience?

To simplify the analysis of neuron firing Signup and view all the answers

What does a neuron primarily rely on to reach an action potential?

Sufficient injected current surpassing threshold Signup and view all the answers

In the integrate-and-fire model, what condition initiates an action potential?

Voltage rising past a threshold value Signup and view all the answers

What is the significance of the integrate-and-fire model's computational simplicity?

It enhances understanding of basic neural principles Signup and view all the answers

What can happen to a neuron if the injected current is too small?

It remains inactive and does not fire Signup and view all the answers

What is the process described that involves injecting a square wave of current into a neuron?

Integrate-and-fire model Signup and view all the answers

In the integrate-and-fire model, what happens to the voltage over time when a square wave of current is injected?

Voltage changes according to the current input Signup and view all the answers

What does the variable 'C' represent in the equation dV(t)/dt = I(t)/C?

Capacitance of the neuron Signup and view all the answers

What does I(t) symbolize in the integrate-and-fire model's equation?

Injected current as a function of time Signup and view all the answers

What is the likely effect on the neuron's voltage if the injected current is held constant over time?

Voltage will increase until a threshold is reached Signup and view all the answers

In the context of the integrate-and-fire model, what does the resting potential refer to?

The baseline voltage of the neuron when not stimulated Signup and view all the answers

If a square wave of current is applied, how does the neuron ideally respond after the current is removed?

It gradually returns to resting potential Signup and view all the answers

In response to a rapid injection of current, which phenomenon is likely to occur?

Threshold reaching and action potential generation Signup and view all the answers

Which parameter primarily affects how quickly a neuron can respond to changes in current?

Capacitance and resistance Signup and view all the answers

When integrated over time, what is the effect of the current on the neuron's membrane potential?

Step-like increase until a threshold is achieved Signup and view all the answers

What is a critical factor in the dynamics of the integrate-and-fire model?

The duration of the current pulse Signup and view all the answers

What typically happens to the voltage at resting potential before any current is applied?

It remains stable Signup and view all the answers

How might varying the amplitude of the square wave of current affect neuronal firing?

Larger amplitude can lead to increased firing rates Signup and view all the answers

What is an expected characteristic of the integrate-and-fire model during sustained current injection?

Consistent periodic firing Signup and view all the answers

Study Notes

Modelling the Mind

Single neuron stimulation can bias decision making in mice trained to lick for a reward.
This means that even a single neuron can influence a complex behavior.

What is a Neuron?

Neurons are the basic units of the nervous system.
They receive input from other neurons through dendrites.
They send signals to other neurons through axons.
The soma processes inputs from dendrites.
Neurons communicate by transmitting action potentials.
Action potentials are all-or-none events, meaning they either happen or they don't.
Frequency coding encodes information: Information is conveyed by the timing or frequency of action potentials, not simply the shape.

The Action Potential

The action potential was first discovered in 1865.
However, important details were not fully understood due to limited technology.
An action potential is caused by the flow of positively charged ions across the cell membrane.
The mechanism behind this flow of ions remained unclear for over a century.

Electrochemical Potential

The membrane potential is the difference in electrical charge between the inside and outside of a neuron.
The membrane potential is influenced by the concentration of ions inside and outside the cell.
Ions are charged particles, and their movement across the cell membrane creates electrical currents.
The membrane is semi-permeable, allowing some ions to pass through while blocking others.

Ion Channels

Ion channels control the permeability of the cell membrane to specific ions.
Ion channels can open and close, allowing or blocking the flow of ions across the membrane.
Ion channels can be triggered by chemical messengers, mechanical forces, or the voltage itself.

Bernstein's Membrane Theory

Proposed that the action potential occurs due to a non-specific increase in membrane permeability, allowing ions to equilibrate and voltage to approach zero.
However, this theory was later found to be incorrect. Experiments showed that the membrane potential actually goes beyond zero during an action potential.

Integrate-and-Fire Model

A phenomenological model that treats the membrane potential as an electrical circuit.
It ignores the mechanism of action potential generation.
This model utilizes physics to understand how a neuron responds to electrical inputs.
It can be represented by a differential equation relating the membrane potential and the flow of charge.
This model helps calculate the voltage at any given time point.

Limitations of the Model

The integrate-and-fire model is a simplified representation of neuron behavior.
While useful for studying neuron dynamics, it doesn't capture all the complexities of information processing in real neurons.

Integrate-and-fire model (1907)

The equation shown is a simplified model of a neuron's behaviour. The model has a single compartment.
Injecting a square wave of current into the neuron causes changes in the membrane potential.
The square wave current I(t) increases the voltage (V(t)) above the resting potential (Vrest).
dV (t) / C = I(t) is a differential equation where C is capacitance which is proportional to the size of the neuron. Increasing I(t) will increase dV(t) and increase V(t).
The equation shows that the rate of change of voltage over time (dV(t)/dt) is equal to the current (I(t)) divided by the capacitance (C).
The change in voltage is proportional to the current, meaning that a larger current will result in a faster rate of change in voltage.
The change in voltage is inversely proportional to the capacitance which means that a smaller neuron will have a larger change in voltage for a given current.

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Description

Explore the fascinating world of neurons and their role in decision-making through this quiz. Learn about the structure of neurons, the action potential, and how they influence complex behaviors. Test your knowledge and discover the intricacies of the nervous system.